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Home » Science Experiments for Kids » Top 5 physics experiments you can try at home
Top 5 physics experiments you can try at home
October 17, 2022 By Emma Vanstone Leave a Comment
Physics is key to understanding the world around us. While some aspects may seem tricky to understand, many fundamental physics concepts can be broken down into simple concepts, some of which can be demonstrated using basic equipment at home.
This list of 5 physics experiments you can try at home is a great starting point for understanding physics and hopefully a source of inspiration for little scientists everywhere!
1. Archimedes and Density
The story behind Archimedes’ discovery of density is that he was asked by the King of Sicily to work out whether a goldsmith had replaced some gold from a crown with silver. Archimedes needed to work out if the goldsmith had cheated without damaging the crown.
The crown weighed the same as the gold the King had given the goldsmith, but gold is more dense than silver so if there was silver in the crown its density would be less than if it was pure gold. Archimedes realised that if he could measure the volume of the crown he could work out its density, but calculating the volume of a crown shape was a tough challenge. According to the story, Archimedes was having a bath one day when he realised that the water level rose as he lowered himself into the bathtub. He realised that the volume of water displaced was equal to the volume of his body in the water.
Archimedes placed the crown in water to work out its density and realised the goldsmith had cheated the king!
Density Experiment
One fun way to demonstrate density is to make a density column. Choose a selection of liquids and place them in density order, from the most dense to the least dense. Carefully pour a small amount of each into a tall jar or glass starting with the most dense. You should end up with a colourful stack of liquids!
2. Split light into the colours of the rainbow
Isaac Newton experimented with prisms and realised that light is made up of different colours ( the colours of the rainbow ). Newton made this discovery in the 1660s. It wasn’t until the 1900s that physicists discovered the electromagnetic spectrum which includes light waves we can’t see, such as microwaves, x-rays waves, infrared and gamma rays.
How to split light
Splitting white light into the colours of the rainbow sounds tricky but all you need is a prism . A prism is a transparent block which is shaped so light bends ( refracts ) as it passes through. Some colours bend more than others so the whole spectrum of colours can be seen.
If you don’t have a prism you can also use a garden hose! Stand with your back to the sun and you’ll see a rainbow in the water! This is because drops of water act like a prism.
3. Speed of Falling Objects
Galileo’s falling objects.
Aristotle thought that heavy objects fell faster than lighter objects, a theory that was later disproved by Galileo .
It is said that Galileo dropped two cannonballs with different weights from the leaning tower of Pisa which hit the ground at the same time. All objects accelerate at the same rate as they fall.
If you drop a feather and a hammer from the same height the hammer will hit the ground first, but this is because of air resistance!
If a hammer and feather are dropped somewhere with no air resistance they hit the ground at the same time. Commander David Scott proved this was true on the Apollo 15 moonwalk!
Hammer and Feather Experiment on the Moon
Brian Cox also proved Galileo’s theory to be correct by doing the same experiment in a vacuum!
While you won’t be able to replicate a hammer or heavy ball and feather falling you can investigate with two objects that are the same size but different weights. This means the air resistance is the same for both objects so the only difference is the weight.
Take two water empty water bottles that are the same size. Fill one to the top with water and leave the other empty. Drop them from the same height. Both will hit the ground at the same time!
4. Newton’s Laws of Motion
Sir Isaac Newton pops up a lot in any physics book as he came up with many of the laws that describe our universe and is undoubtedly one of the most famous scientists of all time. Newton’s Laws of Motion describe how things move and the relationship between a moving object and the forces acting on it.
Making and launching a mini rocket is a great way to learn about Newton’s Laws of Motion .
The rocket remains motionless unless a force acts on it ( Newton’s First Law ).
The acceleration of the rocket is affected by its mass. If you increase the mass of the rocket its acceleration will be less than if it had less mass ( Newton’s Second Law ).
The equal and opposite reaction from the gas forcing the cork downwards propels the rocket upwards ( Newton’s Third Law ).
4. Pressure
Pressure is the force per unit area.
Imagine standing on a lego brick. If you stand on a large brick it will probably hurt, if you stand on a smaller brick with the same force it will hurt more as the pressure is more!
Snow shoes are usually very wide, this is to reduce the pressure on the snow so it sinks less as people walk on it.
Pressure and Eggs
If you stand on one egg, it will most likely break. If you stand on lots of eggs with the same force you increase the area the force is applied over and therefore reduce the pressure on each individual egg.
That’s five easy physics experiments you can do at home! Can you think of any more?
Last Updated on November 9, 2022 by Emma Vanstone
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These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.
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Experiment in Physics
Physics, and natural science in general, is a reasonable enterprise based on valid experimental evidence, criticism, and rational discussion. It provides us with knowledge of the physical world, and it is experiment that provides the evidence that grounds this knowledge. Experiment plays many roles in science. One of its important roles is to test theories and to provide the basis for scientific knowledge. [ 1 ] It can also call for a new theory, either by showing that an accepted theory is incorrect, or by exhibiting a new phenomenon that is in need of explanation. Experiment can provide hints toward the structure or mathematical form of a theory and it can provide evidence for the existence of the entities involved in our theories. Finally, it may also have a life of its own, independent of theory. Scientists may investigate a phenomenon just because it looks interesting. Such experiments may provide evidence for a future theory to explain. [Examples of these different roles will be presented below.] As we shall see below, a single experiment may play several of these roles at once.
If experiment is to play these important roles in science then we must have good reasons to believe experimental results, for science is a fallible enterprise. Theoretical calculations, experimental results, or the comparison between experiment and theory may all be wrong. Science is more complex than “The scientist proposes, Nature disposes.” It may not always be clear what the scientist is proposing. Theories often need to be articulated and clarified. It also may not be clear how Nature is disposing. Experiments may not always give clear-cut results, and may even disagree for a time.
In what follows, the reader will find an epistemology of experiment, a set of strategies that provides reasonable belief in experimental results. Scientific knowledge can then be reasonably based on these experimental results.
1.1 Epistemology of Experiment
1.2.1 ian hacking's case, 1.2.2 experimental strategies, 1.2.3 galison’s elaboration, 1.3.1 collins and the experimenters’ regress, 1.3.2 pickering on communal opportunism and plastic resources, 1.3.3 critical responses to pickering, 1.3.4 pickering and the dance of agency, 1.3.5 hacking’s the social construction of what, 1.3.6 theory-ladenness in high energy physics, 2.1 a life of its own, 2.2.1 a crucial experiment: the discovery of parity nonconservation, 2.2.2 a persuasive experiment: the discovery of cp violation, 2.2.3 confirmation after 70 years: the discovery of bose-einstein condensation, 2.3.1 the fall of the fifth force, 2.3.2 right experiment, wrong theory: the stern-gerlach experiment, 2.3.3 sometimes refutation doesn’t work: the double-scattering of electrons, 2.3.4 the failure to detect anomalies, 2.3.5 the ‘look elsewhere’ effect: discovering the higgs boson, 2.4.1 evidence for a new entity: j.j. thomson and the electron, 2.4.2 the articulation of theory: weak interactions, 2.5.1 epistemological strategies and the peppered moth experiment, 2.5.2 the meselson-stahl experiment: “the most beautiful experiment in biology”, 2.6 computer simulations and experimentation, 2.7 experiment and observation, 3. conclusion, principal works:, other suggested reading, other internet resources, related entries, 1. experimental results.
The 17th century witnessed the first philosophical reflections on the nature of experimentation. This should not be surprising given that experiment was emerging as a central scientific tool at the time. The aim of these reflections was to uncover why nature reveals its hidden aspects to us when we force experimental methods upon it.
Some natural philosophers believed that scientific knowledge was little more than the proper application of observational and experimental techniques on natural phenomena. Francis Bacon went so far as to claim that it was possible to perform what he called a crucial experiment (experimentum crucis), an ideal experiment of sorts that can determine alone which of two rival hypotheses is correct. And even some of the giants of modern science such as Newton subscribed to the view that scientific theories are directly induced from experimental results and observations without the help of untested hypotheses. It is little wonder, then, that many natural philosophers thought that experimental techniques and their proper application should be a primary object of philosophical study of science.
Thomas Kuhn and Paul Feyerabend vigorously criticized this view. They argued that observations and experimental results are already part of a theoretical framework and thus cannot confirm a theory independently. Nor there is a theory-neutral language for capturing observations. Even a simple reading of a mercury thermometer inevitably depends on a theoretically-charged concept of temperature. In short, the evidence is always theory-laden.
Yet neither the proponents of logical positivism nor their critics ever attempted to explain the nature of experimentation that produces all-important observational statements. And the reason for this was very simple: they didn’t think that there was anything interesting to explain. Their views on the relationship between theory and evidence were diametrically opposed, but they all found only the final product of experimentation, namely observational statements, philosophically interesting. As a result, the experimental process itself was set aside in their philosophical study of science. This has gradually changed only with the advent of New Experimentalism, with Ian Hacking’s work at its forefront.
Yet not everybody agreed. Hobbes, for instance pointed out that human reason preceded experimental techniques and their application. He thought that human reasoning reveals to us the natural law, and criticized Boyle’s optimism regarding experimental method’s ability to reveal it (Shapin and Schaffer 1984). Doesn’t human reason guide experimenter’s actions, in the way it leads us to choose data and samples, and the way it allows us to interpret them, after all? If so, we should focus on the philosophical study of reason and theoretical scientific reasoning rather than on the study of experimental techniques and their applications.
This vigorous early debate in many ways anticipated the main points of disagreement in debates to come. Yet the philosophical interest in experimentation almost completely lost its steam at the end of the 19th century and did not recover until fairly late in the 20th century.
During that period philosophers turned much of their attention to the study of the logical structure of scientific theories and its connection to evidence. The tenets of logical positivism influenced this area of investigation — as well as philosophy more generally — at the time. One of these tenets stated that observational and theoretical propositions in science are separable. My readings of the gradation on the scale of a mercury thermometer can be separated from rather complicated theoretical statements concerning heat transfer and the theoretical concept of temperature.
In fact, not only can one separate theory and observation, but the former is considered justified only in light of its correspondence with the latter. The theory of heat transfer is confirmed by propositions originating in the kind of readings I perform on my mercury thermometer. Thus, observational propositions are simply a result of an experiment or a set of observations a scientist performs in order to confirm or refute a theory.
1.2 The Case For Learning From Experiment
It has been almost four decades since Ian Hacking asked, “Do we see through a microscope?” (Hacking 1981). Hacking’s question really asked how do we come to believe in an experimental result obtained with a complex experimental apparatus? How do we distinguish between a valid result [ 2 ] and an artifact created by that apparatus? If experiment is to play all of the important roles in science mentioned above and to provide the evidential basis for scientific knowledge, then we must have good reasons to believe in those results. Hacking provided an extended answer in the second half of Representing and Intervening (1983). He pointed out that even though an experimental apparatus is laden with, at the very least, the theory of the apparatus, observations remain robust despite changes in the theory of the apparatus or in the theory of the phenomenon. His illustration was the sustained belief in microscope images despite the major change in the theory of the microscope when Abbe pointed out the importance of diffraction in its operation. One reason Hacking gave for this is that in making such observations the experimenters intervened—they manipulated the object under observation. Thus, in looking at a cell through a microscope, one might inject fluid into the cell or stain the specimen. One expects the cell to change shape or color when this is done. Observing the predicted effect strengthens our belief in both the proper operation of the microscope and in the observation. This is true in general. Observing the predicted effect of an intervention strengthens our belief in both the proper operation of the experimental apparatus and in the observations made with it.
Hacking also discussed the strengthening of one’s belief in an observation by independent confirmation. The fact that the same pattern of dots—dense bodies in cells—is seen with “different” microscopes, (e.g. ordinary, polarizing, phase-contrast, fluorescence, interference, electron, acoustic etc.) argues for the validity of the observation. One might question whether “different” is a theory-laden term. After all, it is our theory of light and of the microscope that allows us to consider these microscopes as different from each other. Nevertheless, the argument holds. Hacking correctly argues that it would be a preposterous coincidence if the same pattern of dots were produced in two totally different kinds of physical systems. Different apparatuses have different backgrounds and systematic errors, making the coincidence, if it is an artifact, most unlikely. If it is a correct result, and the instruments are working properly, the coincidence of results is understandable.
Hacking’s answer is correct as far as it goes. It is, however, incomplete. What happens when one can perform the experiment with only one type of apparatus, such as an electron microscope or a radio telescope, or when intervention is either impossible or extremely difficult? Other strategies are needed to validate the observation. [ 3 ] These may include:
- Experimental checks and calibration, in which the experimental apparatus reproduces known phenomena. For example, if we wish to argue that the spectrum of a substance obtained with a new type of spectrometer is correct, we might check that this new spectrometer could reproduce the known Balmer series in hydrogen. If we correctly observe the Balmer Series then we strengthen our belief that the spectrometer is working properly. This also strengthens our belief in the results obtained with that spectrometer. If the check fails then we have good reason to question the results obtained with that apparatus.
- Reproducing artifacts that are known in advance to be present. An example of this comes from experiments to measure the infrared spectra of organic molecules (Randall et al. 1949). It was not always possible to prepare a pure sample of such material. Sometimes the experimenters had to place the substance in an oil paste or in solution. In such cases, one expects to observe the spectrum of the oil or the solvent, superimposed on that of the substance. One can then compare the composite spectrum with the known spectrum of the oil or the solvent. Observation then of this artifact gives confidence in other measurements made with the spectrometer.
- Elimination of plausible sources of error and alternative explanations of the result (the Sherlock Holmes strategy). [ 4 ] Thus, when scientists claimed to have observed electric discharges in the rings of Saturn, they argued for their result by showing that it could not have been caused by defects in the telemetry, interaction with the environment of Saturn, lightning, or dust. The only remaining explanation of their result was that it was due to electric discharges in the rings—there was no other plausible explanation of the observation. (In addition, the same result was observed by both Voyager 1 and Voyager 2. This provided independent confirmation. Often, several epistemological strategies are used in the same experiment.)
- Using the results themselves to argue for their validity. Consider the problem of Galileo’s telescopic observations of the moons of Jupiter. Although one might very well believe that his primitive, early telescope might have produced spurious spots of light, it is extremely implausible that the telescope would create images that they would appear to be a eclipses and other phenomena consistent with the motions of a small planetary system. It would have been even more implausible to believe that the created spots would satisfy Kepler’s Third Law (\(\bfrac{R^3}{T^2} = \) constant). A similar argument was used by Robert Millikan to support his observation of the quantization of electric charge and his measurement of the charge of the electron. Millikan remarked, “The total number of changes which we have observed would be between one and two thousand, and in not one single instance has there been any change which did not represent the advent upon the drop of one definite invariable quantity of electricity or a very small multiple of that quantity ” (Millikan 1911, p. 360). In both of these cases one is arguing that there was no plausible malfunction of the apparatus, or background, that would explain the observations.
- Using an independently well-corroborated theory of the phenomena to explain the results. This was illustrated in the discovery of the \(\ce{W^{\pm}}\), the charged intermediate vector boson required by the Weinberg-Salam unified theory of electroweak interactions. Although these experiments used very complex apparatuses and used other epistemological strategies (for details see (Franklin 1986, pp. 170–72)). I believe that the agreement of the observations with the theoretical predictions of the particle properties helped to validate the experimental results. In this case the particle candidates were observed in events that contained an electron with high transverse momentum and in which there were no particle jets, just as predicted by the theory. In addition, the measured particle mass of \(81\pm 5\) GeV/c 2 and \(80^{+10}_{-6}\) GeV/c 2 , found in the two experiments (note the independent confirmation also), was in good agreement with the theoretical prediction of \(82\pm 2.4\) GeV/c 2 . It was very improbable that any background effect, which might mimic the presence of the particle, would be in agreement with theory.
- Using an apparatus based on a well-corroborated theory. In this case the support for the theory inspires confidence in the apparatus based on that theory. This is the case with the electron microscope and the radio telescope, whose operations are based on a well-supported theories, although other strategies are also used to validate the observations made with these instruments.
- Using statistical arguments. An interesting example of this arose in the 1960s when the search for new particles and resonances occupied a substantial fraction of the time and effort of those physicists working in experimental high-energy physics. The usual technique was to plot the number of events observed as a function of the invariant mass of the final-state particles and to look for bumps above a smooth background. The usual informal criterion for the presence of a new particle was that it resulted in a three standard-deviation effect above the background, a result that had a probability of 0.27% of occurring in a single bin. This criterion was later changed to four standard deviations, which had a probability of 0.0064% when it was pointed out that the number of graphs plotted each year by high-energy physicists made it rather probable, on statistical grounds, that a three standard-deviation effect would be observed.
These strategies along with Hacking’s intervention and independent confirmation constitute an epistemology of experiment. They provide us with good reasons for belief in experimental results, They do not, however, guarantee that the results are correct. There are many experiments in which these strategies are applied, but whose results are later shown to be incorrect (examples will be presented below). Experiment is fallible. Neither are these strategies exclusive or exhaustive. No single one of them, or fixed combination of them, guarantees the validity of an experimental result. Physicists use as many of the strategies as they can conveniently apply in any given experiment.
In How Experiments End (1987), Peter Galison extended the discussion of experiment to more complex situations. In his histories of the measurements of the gyromagnetic ratio of the electron, the discovery of the muon, and the discovery of weak neutral currents, he considered a series of experiments measuring a single quantity, a set of different experiments culminating in a discovery, and two high- energy physics experiments performed by large groups with complex experimental apparatus.
Galison’s view is that experiments end when the experimenters believe that they have a result that will stand up in court—a result that I believe includes the use of the epistemological strategies discussed earlier. Thus, David Cline, one of the weak neutral-current experimenters remarked, “At present I don’t see how to make these effects [the weak neutral current event candidates] go away” (Galison, 1987, p. 235).
Galison emphasizes that, within a large experimental group, different members of the group may find different pieces of evidence most convincing. Thus, in the Gargamelle weak neutral current experiment, several group members found the single photograph of a neutrino-electron scattering event particularly important, whereas for others the difference in spatial distribution between the observed neutral current candidates and the neutron background was decisive. Galison attributes this, in large part, to differences in experimental traditions, in which scientists develop skill in using certain types of instruments or apparatus. In particle physics, for example, there is the tradition of visual detectors, such as the cloud chamber or the bubble chamber, in contrast to the electronic tradition of Geiger and scintillation counters and spark chambers. Scientists within the visual tradition tend to prefer “golden events” that clearly demonstrate the phenomenon in question, whereas those in the electronic tradition tend to find statistical arguments more persuasive and important than individual events. (For further discussion of this issue see Galison (1997)).
Galison points out that major changes in theory and in experimental practice and instruments do not necessarily occur at the same time. This persistence of experimental results provides continuity across these conceptual changes. Thus, the experiments on the gyromagnetic ratio spanned classical electromagnetism, Bohr’s old quantum theory, and the new quantum mechanics of Heisenberg and Schrodinger. Robert Ackermann has offered a similar view in his discussion of scientific instruments.
The advantages of a scientific instrument are that it cannot change theories. Instruments embody theories, to be sure, or we wouldn’t have any grasp of the significance of their operation….Instruments create an invariant relationship between their operations and the world, at least when we abstract from the expertise involved in their correct use. When our theories change, we may conceive of the significance of the instrument and the world with which it is interacting differently, and the datum of an instrument may change in significance, but the datum can nonetheless stay the same, and will typically be expected to do so. An instrument reads 2 when exposed to some phenomenon. After a change in theory, [ 5 ] it will continue to show the same reading, even though we may take the reading to be no longer important, or to tell us something other than what we thought originally (Ackermann 1985, p. 33).
Galison also discusses other aspects of the interaction between experiment and theory. Theory may influence what is considered to be a real effect, demanding explanation, and what is considered background. In his discussion of the discovery of the muon, he argues that the calculation of Oppenheimer and Carlson, which showed that showers were to be expected in the passage of electrons through matter, left the penetrating particles, later shown to be muons, as the unexplained phenomenon. Prior to their work, physicists thought the showering particles were the problem, whereas the penetrating particles seemed to be understood.
The role of theory as an “enabling theory,” (i.e., one that allows calculation or estimation of the size of the expected effect and also the size of expected backgrounds) is also discussed by Galison. (See also (Franklin 1995) and the discussion of the Stern-Gerlach experiment below). Such a theory can help to determine whether an experiment is feasible. Galison also emphasizes that elimination of background that might simulate or mask an effect is central to the experimental enterprise, and not a peripheral activity. In the case of the weak neutral current experiments, the existence of the currents depended crucially on showing that the event candidates could not all be due to neutron background. [ 6 ]
There is also a danger that the design of an experiment may preclude observation of a phenomenon. Galison points out that the original design of one of the neutral current experiments, which included a muon trigger, would not have allowed the observation of neutral currents. In its original form the experiment was designed to observe charged currents, which produce a high energy muon. Neutral currents do not. Therefore, having a muon trigger precluded their observation. Only after the theoretical importance of the search for neutral currents was emphasized to the experimenters was the trigger changed. Changing the design did not, of course, guarantee that neutral currents would be observed.
Galison also shows that the theoretical presuppositions of the experimenters may enter into the decision to end an experiment and report the result. Einstein and de Haas ended their search for systematic errors when their value for the gyromagnetic ratio of the electron, \(g = 1\), agreed with their theoretical model of orbiting electrons. This effect of presuppositions might cause one to be skeptical of both experimental results and their role in theory evaluation. Galison’s history shows, however, that, in this case, the importance of the measurement led to many repetitions of the measurement. This resulted in an agreed-upon result that disagreed with theoretical expectations.
Recently, Galison has modified his views. In Image and Logic , an extended study of instrumentation in 20th-century high-energy physics, Galison (1997) has extended his argument that there are two distinct experimental traditions within that field—the visual (or image) tradition and the electronic (or logic) tradition. The image tradition uses detectors such as cloud chambers or bubble chambers, which provide detailed and extensive information about each individual event. The electronic detectors used by the logic tradition, such as geiger counters, scintillation counters, and spark chambers, provide less detailed information about individual events, but detect more events. Galison’s view is that experimenters working in these two traditions form distinct epistemic and linguistic groups that rely on different forms of argument. The visual tradition emphasizes the single “golden” event. “On the image side resides a deep-seated commitment to the ‘golden event’: the single picture of such clarity and distinctness that it commands acceptance.” (Galison, 1997, p. 22) “The golden event was the exemplar of the image tradition: an individual instance so complete and well defined, so ‘manifestly’ free of distortion and background that no further data had to be involved” (p. 23). Because the individual events provided in the logic detectors contained less detailed information than the pictures of the visual tradition, statistical arguments based on large numbers of events were required.
Kent Staley (1999) disagrees. He argues that the two traditions are not as distinct as Galison believes:
I show that discoveries in both traditions have employed the same statistical [I would add “and/or probabilistic”] form of argument, even when basing discovery claims on single, golden events. Where Galison sees an epistemic divide between two communities that can only be bridged by creole- or pidgin-like ‘interlanguage,’ there is in fact a shared commitment to a statistical form of experimental argument. (p. 96).
Staley believes that although there is certainly epistemic continuity within a given tradition, there is also a continuity between the traditions. This does not, I believe, mean that the shared commitment comprises all of the arguments offered in any particular instance, but rather that the same methods are often used by both communities. Galison does not deny that statistical methods are used in the image tradition, but he thinks that they are relatively unimportant. “While statistics could certainly be used within the image tradition, it was by no means necessary for most applications” (Galison, 1997, p. 451). In contrast, Galison believes that arguments in the logic tradition “were inherently and inalienably statistical. Estimation of probable errors and the statistical excess over background is not a side issue in these detectors—it is central to the possibility of any demonstration at all” (p. 451).
Although a detailed discussion of the disagreement between Staley and Galison would take us too far from the subject of this essay, they both agree that arguments are offered for the correctness of experimental results. Their disagreement concerns the nature of those arguments. (For further discussion see Franklin, (2002), pp. 9–17).
1.3 The Case Against Learning From Experiment
Collins, Pickering, and others, have raised objections to the view that experimental results are accepted on the basis of epistemological arguments. They point out that “a sufficiently determined critic can always find a reason to dispute any alleged ‘result’” (MacKenzie 1989, p. 412). Harry Collins, for example, is well known for his skepticism concerning both experimental results and evidence. He develops an argument that he calls the “experimenters’ regress” (Collins 1985, chapter 4, pp. 79–111): What scientists take to be a correct result is one obtained with a good, that is, properly functioning, experimental apparatus. But a good experimental apparatus is simply one that gives correct results. Collins claims that there are no formal criteria that one can apply to decide whether or not an experimental apparatus is working properly. In particular, he argues that calibrating an experimental apparatus by using a surrogate signal cannot provide an independent reason for considering the apparatus to be reliable.
In Collins’ view the regress is eventually broken by negotiation within the appropriate scientific community, a process driven by factors such as the career, social, and cognitive interests of the scientists, and the perceived utility for future work, but one that is not decided by what we might call epistemological criteria, or reasoned judgment. Thus, Collins concludes that his regress raises serious questions concerning both experimental evidence and its use in the evaluation of scientific hypotheses and theories. Indeed, if no way out of the regress can be found, then he has a point.
Collins strongest candidate for an example of the experimenters’ regress is presented in his history of the early attempts to detect gravitational radiation, or gravity waves. (For more detailed discussion of this episode see (Collins 1985; 1994; Franklin 1994; 1997a) In this case, the physics community was forced to compare Weber’s claims that he had observed gravity waves with the reports from six other experiments that failed to detect them. On the one hand, Collins argues that the decision between these conflicting experimental results could not be made on epistemological or methodological grounds—he claims that the six negative experiments could not legitimately be regarded as replications [ 7 ] and hence become less impressive. On the other hand, Weber’s apparatus, precisely because the experiments used a new type of apparatus to try to detect a hitherto unobserved phenomenon, [ 8 ] could not be subjected to standard calibration techniques.
The results presented by Weber’s critics were not only more numerous, but they had also been carefully cross-checked. The groups had exchanged both data and analysis programs and confirmed their results. The critics had also investigated whether or not their analysis procedure, the use of a linear algorithm, could account for their failure to observe Weber’s reported results. They had used Weber’s preferred procedure, a nonlinear algorithm, to analyze their own data, and still found no sign of an effect. They had also calibrated their experimental apparatuses by inserting acoustic pulses of known energy and finding that they could detect a signal. Weber, on the other hand, as well as his critics using his analysis procedure, could not detect such calibration pulses.
There were, in addition, several other serious questions raised about Weber’s analysis procedures. These included an admitted programming error that generated spurious coincidences between Weber’s two detectors, possible selection bias by Weber, Weber’s report of coincidences between two detectors when the data had been taken four hours apart, and whether or not Weber’s experimental apparatus could produce the narrow coincidences claimed.
It seems clear that the critics’ results were far more credible than Weber’s. They had checked their results by independent confirmation, which included the sharing of data and analysis programs. They had also eliminated a plausible source of error, that of the pulses being longer than expected, by analyzing their results using the nonlinear algorithm and by explicitly searching for such long pulses. [ 9 ] They had also calibrated their apparatuses by injecting pulses of known energy and observing the output.
Contrary to Collins, I believe that the scientific community made a reasoned judgment and rejected Weber’s results and accepted those of his critics. Although no formal rules were applied (e.g. if you make four errors, rather than three, your results lack credibility; or if there are five, but not six, conflicting results, your work is still credible) the procedure was reasonable.
Pickering has argued that the reasons for accepting results are the future utility of such results for both theoretical and experimental practice and the agreement of such results with the existing community commitments. In discussing the discovery of weak neutral currents, Pickering states,
Quite simply, particle physicists accepted the existence of the neutral current because they could see how to ply their trade more profitably in a world in which the neutral current was real. (1984b, p. 87) Scientific communities tend to reject data that conflict with group commitments and, obversely, to adjust their experimental techniques to tune in on phenomena consistent with those commitments. (1981, p. 236)
The emphasis on future utility and existing commitments is clear. These two criteria do not necessarily agree. For example, there are episodes in the history of science in which more opportunity for future work is provided by the overthrow of existing theory. (See, for example, the history of the overthrow of parity conservation and of CP symmetry discussed below and in (Franklin 1986, Ch. 1, 3)).
Pickering has recently offered a different view of experimental results. In his view the material procedure (including the experimental apparatus itself along with setting it up, running it, and monitoring its operation), the theoretical model of that apparatus, and the theoretical model of the phenomena under investigation are all plastic resources that the investigator brings into relations of mutual support. (Pickering 1987; Pickering 1989). He says:
Achieving such relations of mutual support is, I suggest, the defining characteristic of the successful experiment. (1987, p. 199)
He uses Morpurgo’s search for free quarks, or fractional charges of \(\tfrac{1}{3} e\) or \(\tfrac{2}{3} e\), where \(e\) is the charge of the electron. (See also (Gooding 1992)). Morpurgo used a modern Millikan-type apparatus and initially found a continuous distribution of charge values. Following some tinkering with the apparatus, Morpurgo found that if he separated the capacitor plates he obtained only integral values of charge. “After some theoretical analysis, Morpurgo concluded that he now had his apparatus working properly, and reported his failure to find any evidence for fractional charges” (Pickering 1987, p. 197).
Pickering goes on to note that Morpurgo did not tinker with the two competing theories of the phenomena then on offer, those of integral and fractional charge:
The initial source of doubt about the adequacy of the early stages of the experiment was precisely the fact that their findings—continuously distributed charges—were consonant with neither of the phenomenal models which Morpurgo was prepared to countenance. And what motivated the search for a new instrumental model was Morpurgo’s eventual success in producing findings in accordance with one of the phenomenal models he was willing to accept The conclusion of Morpurgo’s first series of experiments, then, and the production of the observation report which they sustained, was marked by bringing into relations of mutual support of the three elements I have discussed: the material form of the apparatus and the two conceptual models, one instrumental and the other phenomenal. Achieving such relations of mutual support is, I suggest, the defining characteristic of the successful experiment. (p. 199)
Pickering has made several important and valid points concerning experiment. Most importantly, he has emphasized that an experimental apparatus is initially rarely capable of producing a valid experimental results and that some adjustment, or tinkering, is required before it does. He has also recognized that both the theory of the apparatus and the theory of the phenomena can enter into the production of a valid experimental result. What one may question, however, is the emphasis he places on these theoretical components. From Millikan onwards, experiments had strongly supported the existence of a fundamental unit of charge and charge quantization. The failure of Morpurgo’s apparatus to produce measurements of integral charge indicated that it was not operating properly and that his theoretical understanding of it was faulty. It was the failure to produce measurements in agreement with what was already known (i.e., the failure of an important experimental check) that caused doubts about Morpurgo’s measurements. This was true regardless of the theoretical models available, or those that Morpurgo was willing to accept. It was only when Morpurgo’s apparatus could reproduce known measurements that it could be trusted and used to search for fractional charge. To be sure, Pickering has allowed a role for the natural world in the production of the experimental result, but it does not seem to be decisive.
Ackermann has offered a modification of Pickering’s view. He suggests that the experimental apparatus itself is a less plastic resource then either the theoretical model of the apparatus or that of the phenomenon.
To repeat, changes in \(A\) [the apparatus] can often be seen (in real time, without waiting for accommodation by \(B\) [the theoretical model of the apparatus]) as improvements, whereas ‘improvements’ in \(B\) don’t begin to count unless \(A\) is actually altered and realizes the improvements conjectured. It’s conceivable that this small asymmetry can account, ultimately, for large scale directions of scientific progress and for the objectivity and rationality of those directions. (Ackermann 1991, p. 456)
Hacking (1992) has also offered a more complex version of Pickering’s later view. He suggests that the results of mature laboratory science achieve stability and are self-vindicating when the elements of laboratory science are brought into mutual consistency and support. These are (1) ideas: questions, background knowledge, systematic theory, topical hypotheses, and modeling of the apparatus; (2) things: target, source of modification, detectors, tools, and data generators; and (3) marks and the manipulation of marks: data, data assessment, data reduction, data analysis, and interpretation.
Stable laboratory science arises when theories and laboratory equipment evolve in such a way that they match each other and are mutually self-vindicating. (1992, p. 56) We invent devices that produce data and isolate or create phenomena, and a network of different levels of theory is true to these phenomena. Conversely we may in the end count them only as phenomena only when the data can be interpreted by theory. (pp. 57–8)
One might ask whether such mutual adjustment between theory and experimental results can always be achieved? What happens when an experimental result is produced by an apparatus on which several of the epistemological strategies, discussed earlier, have been successfully applied, and the result is in disagreement with our theory of the phenomenon? Accepted theories can be refuted. Several examples will be presented below.
Hacking himself worries about what happens when a laboratory science that is true to the phenomena generated in the laboratory, thanks to mutual adjustment and self-vindication, is successfully applied to the world outside the laboratory. Does this argue for the truth of the science. In Hacking’s view it does not. If laboratory science does produce happy effects in the “untamed world,… it is not the truth of anything that causes or explains the happy effects” (1992, p. 60).
Recently Pickering has offered a somewhat revised account of science. “My basic image of science is a performative one, in which the performances the doings of human and material agency come to the fore. Scientists are human agents in a field of material agency which they struggle to capture in machines (Pickering, 1995, p. 21).” He then discusses the complex interaction between human and material agency, which I interpret as the interaction between experimenters, their apparatus, and the natural world.
The dance of agency, seen asymmetrically from the human end, thus takes the form of a dialectic of resistance and accommodations, where resistance denotes the failure to achieve an intended capture of agency in practice, and accommodation an active human strategy of response to resistance, which can include revisions to goals and intentions as well as to the material form of the machine in question and to the human frame of gestures and social relations that surround it (p. 22).“
Pickering’s idea of resistance is illustrated by Morpurgo’s observation of continuous, rather than integral or fractional, electrical charge, which did not agree with his expectations. Morpurgo’s accommodation consisted of changing his experimental apparatus by using a larger separation between his plates, and also by modifying his theoretical account of the apparatus. That being done, integral charges were observed and the result stabilized by the mutual agreement of the apparatus, the theory of the apparatus, and the theory of the phenomenon. Pickering notes that ”the outcomes depend on how the world is (p. 182).“ ”In this way, then, how the material world is leaks into and infects our representations of it in a nontrivial and consequential fashion. My analysis thus displays an intimate and responsive engagement between scientific knowledge and the material world that is integral to scientific practice (p. 183).“
Nevertheless there is something confusing about Pickering’s invocation of the natural world. Although Pickering acknowledges the importance of the natural world, his use of the term ”infects“ seems to indicate that he isn’t entirely happy with this. Nor does the natural world seem to have much efficacy. It never seems to be decisive in any of Pickering’s case studies. Recall that he argued that physicists accepted the existence of weak neutral currents because ”they could ply their trade more profitably in a world in which the neutral current was real.“ In his account, Morpurgo’s observation of continuous charge is important only because it disagrees with his theoretical models of the phenomenon. The fact that it disagreed with numerous previous observations of integral charge doesn’t seem to matter. This is further illustrated by Pickering’s discussion of the conflict between Morpurgo and Fairbank. As we have seen, Morpurgo reported that he did not observe fractional electrical charges. On the other hand, in the late 1970s and early 1980s, Fairbank and his collaborators published a series of papers in which they claimed to have observed fractional charges (See, for example, LaRue, Phillips et al. 1981 ). Faced with this discord Pickering concludes,
In Chapter 3, I traced out Morpurgo’s route to his findings in terms of the particular vectors of cultural extension that he pursued, the particular resistances and accommodations thus precipitated, and the particular interactive stabilizations he achieved. The same could be done, I am sure, in respect of Fairbank. And these tracings are all that needs to said about their divergence. It just happened that the contingencies of resistance and accommodation worked out differently in the two instances. Differences like these are, I think, continually bubbling up in practice, without any special causes behind them (pp. 211–212).
The natural world seems to have disappeared from Pickering’s account. There is a real question here as to whether or not fractional charges exist in nature. The conclusions reached by Fairbank and by Morpurgo about their existence cannot both be correct. It seems insufficient to merely state, as Pickering does, that Fairbank and Morpurgo achieved their individual stabilizations and to leave the conflict unresolved. (Pickering does comment that one could follow the subsequent history and see how the conflict was resolved, and he does give some brief statements about it, but its resolution is not important for him). At the very least one should consider the actions of the scientific community. Scientific knowledge is not determined individually, but communally. Pickering seems to acknowledge this. ”One might, therefore, want to set up a metric and say that items of scientific knowledge are more or less objective depending on the extent to which they are threaded into the rest of scientific culture, socially stabilized over time, and so on. I can see nothing wrong with thinking this way…. (p. 196).“ The fact that Fairbank believed in the existence of fractional electrical charges, or that Weber strongly believed that he had observed gravity waves, does not make them right. These are questions about the natural world that can be resolved. Either fractional charges and gravity waves exist or they don’t, or to be more cautious we might say that we have good reasons to support our claims about their existence, or we do not.
Another issue neglected by Pickering is the question of whether a particular mutual adjustment of theory, of the apparatus or the phenomenon, and the experimental apparatus and evidence is justified. Pickering seems to believe that any such adjustment that provides stabilization, either for an individual or for the community, is acceptable. Others disagree. They note that experimenters sometimes exclude data and engage in selective analysis procedures in producing experimental results. These practices are, at the very least, questionable as is the use of the results produced by such practices in science. There are, in fact, procedures in the normal practice of science that provide safeguards against them. (For details see Franklin, 2002, Section 1).
The difference in attitudes toward the resolution of discord is one of the important distinctions between Pickering’s and Franklin’s view of science. Franklin remarks that it is insufficient simply to say that the resolution is socially stabilized. The important question is how that resolution was achieved and what were the reasons offered for that resolution. If we are faced with discordant experimental results and both experimenters have offered reasonable arguments for their correctness, then clearly more work is needed. It seems reasonable, in such cases, for the physics community to search for an error in one, or both, of the experiments.
Pickering discusses yet another difference between his view and that of Franklin. Pickering sees traditional philosophy of science as regarding objectivity ”as stemming from a peculiar kind of mental hygiene or policing of thought. This police function relates specifically to theory choice in science, which,… is usually discussed in terms of the rational rules or methods responsible for closure in theoretical debate (p. 197).“ He goes on to remark that,
The most action in recent methodological thought has centered on attempts like Allan Franklin’s to extend the methodological approach to experiments by setting up a set of rules for their proper performance. Franklin thus seeks to extend classical discussions of objectivity to the empirical base of science (a topic hitherto neglected in the philosophical tradition but one that, of course the mangle [Pickering’s view] also addresses). For an argument between myself and Franklin on the same lines as that laid out below, see (Franklin 1990, Chapter 8; Franklin 1991); and (Pickering 1991); and for commentaries related to that debate, (Ackermann 1991) and (Lynch 1991) (p. 197).”
For further discussion see (Franklin 1993b)). Although Franklin’s epistemology of experiment is designed to offer good reasons for belief in experimental results, they are not a set of rules. Franklin regards them as a set of strategies, from which physicists choose, in order to argue for the correctness of their results. As noted above, the strategies offered are neither exclusive or exhaustive.
There is another point of disagreement between Pickering and Franklin. Pickering claims to be dealing with the practice of science, and yet he excludes certain practices from his discussions. One scientific practice is the application of the epistemological strategies outlined above to argue for the correctness of an experimental results. In fact, one of the essential features of an experimental paper is the presentation of such arguments. Writing such papers, a performative act, is also a scientific practice and it would seem reasonable to examine both the structure and content of those papers.
Recently Ian Hacking (1999, chapter 3) has provided an incisive and interesting discussion of the issues that divide the constructivists (Collins, Pickering, etc.) from the rationalists (Stuewer, Franklin, Buchwald, etc.). He sets out three sticking points between the two views: 1) contingency, 2) nominalism, and 3) external explanations of stability.
Contingency is the idea that science is not predetermined, that it could have developed in any one of several successful ways. This is the view adopted by constructivists. Hacking illustrates this with Pickering’s account of high-energy physics during the 1970s during which the quark model came to dominate. (See Pickering 1984a).
The constructionist maintains a contingency thesis. In the case of physics, (a) physics theoretical, experimental, material) could have developed in, for example, a nonquarky way, and, by the detailed standards that would have evolved with this alternative physics, could have been as successful as recent physics has been by its detailed standards. Moreover, (b) there is no sense in which this imagined physics would be equivalent to present physics. The physicist denies that. (Hacking 1999, pp. 78–79). To sum up Pickering’s doctrine: there could have been a research program as successful (“progressive”) as that of high-energy physics in the 1970s, but with different theories, phenomenology, schematic descriptions of apparatus, and apparatus, and with a different, and progressive, series of robust fits between these ingredients. Moreover and this is something badly in need of clarification the “different” physics would not have been equivalent to present physics. Not logically incompatible with, just different. The constructionist about (the idea) of quarks thus claims that the upshot of this process of accommodation and resistance is not fully predetermined. Laboratory work requires that we get a robust fit between apparatus, beliefs about the apparatus, interpretations and analyses of data, and theories. Before a robust fit has been achieved, it is not determined what that fit will be. Not determined by how the world is, not determined by technology now in existence, not determined by the social practices of scientists, not determined by interests or networks, not determined by genius, not determined by anything (pp. 72–73, emphasis added).
Much depends here on what Hacking means by “determined.” If he means entailed then one must agree with him. It is doubtful that the world, or more properly, what we can learn about it, entails a unique theory. If not, as seems more plausible, he means that the way the world is places no restrictions on that successful science, then the rationalists disagree strongly. They want to argue that the way the world is restricts the kinds of theories that will fit the phenomena, the kinds of apparatus we can build, and the results we can obtain with such apparatuses. To think otherwise seems silly. Consider a homey example. It seems highly unlikely that someone can come up with a successful theory in which objects whose density is greater than that of air fall upwards. This is not a caricature of the view Hacking describes. Describing Pickering’s view, he states, “Physics did not need to take a route that involved Maxwell’s Equations, the Second Law of Thermodynamics, or the present values of the velocity of light (p. 70).” Although one may have some sympathy for this view as regards Maxwell’s Equations or the Second Law of Thermodynamics, one may not agree about the value of the speed of light. That is determined by the way the world is. Any successful theory of light must give that value for its speed.
At the other extreme are the “inevitablists,” among whom Hacking classifies most scientists. He cites Sheldon Glashow, a Nobel Prize winner, “Any intelligent alien anywhere would have come upon the same logical system as we have to explain the structure of protons and the nature of supernovae (Glashow 1992, p. 28).”
Another difference between Pickering and Franklin on contingency concerns the question of not whether an alternative is possible, but rather whether there are reasons why that alternative should be pursued. Pickering seems to identify can with ought .
In the late 1970s there was a disagreement between the results of low-energy experiments on atomic parity violation (the violation of left-right symmetry) performed at the University of Washington and at Oxford University and the result of a high-energy experiment on the scattering of polarized electrons from deuterium (the SLAC E122 experiment). The atomic-parity violation experiments failed to observe the parity-violating effects predicted by the Weinberg- Salam (W-S) unified theory of electroweak interactions, whereas the SLAC experiment observed the predicted effect. These early atomic physics results were quite uncertain in themselves and that uncertainty was increased by positive results obtained in similar experiments at Berkeley and Novosibirsk. At the time the theory had other evidential support, but was not universally accepted. Pickering and Franklin are in agreement that the W-S theory was accepted on the basis of the SLAC E122 result. They differ dramatically in their discussions of the experiments. Their difference on contingency concerns a particular theoretical alternative that was proposed at the time to explain the discrepancy between the experimental results.
Pickering asked why a theorist might not have attempted to find a variant of electroweak gauge theory that might have reconciled the Washington-Oxford atomic parity results with the positive E122 result. (What such a theorist was supposed to do with the supportive atomic parity results later provided by experiments at Berkeley and at Novosibirsk is never mentioned). “But though it is true that E122 analysed their data in a way that displayed the improbability [the probability of the fit to the hybrid model was 6 × 10 −4 ] of a particular class of variant gauge theories, the so-called ‘hybrid models,’ I do not believe that it would have been impossible to devise yet more variants” (Pickering 1991, p. 462). Pickering notes that open-ended recipes for constructing such variants had been written down as early as 1972 (p. 467). It would have been possible to do so, but one may ask whether or not a scientist might have wished to do so. If the scientist agreed with Franklin’s view that the SLAC E122 experiment provided considerable evidential weight in support of the W-S theory and that a set of conflicting and uncertain results from atomic parity-violation experiments gave an equivocal answer on that support, what reason would they have had to invent an alternative?
This is not to suggest that scientists do not, or should not, engage in speculation, but rather that there was no necessity to do so in this case. Theorists often do propose alternatives to existing, well-confirmed theories.
Constructivist case studies always seem to result in the support of existing, accepted theory (Pickering 1984a; 1984b; 1991; Collins 1985; Collins and Pinch 1993). One criticism implied in such cases is that alternatives are not considered, that the hypothesis space of acceptable alternatives is either very small or empty. One may seriously question this. Thus, when the experiment of Christenson et al . (1964) detected \(\ce{K2^0}\) decay into two pions, which seemed to show that CP symmetry (combined particle-antiparticle and space inversion symmetry) was violated, no fewer than 10 alternatives were offered. These included (1) the cosmological model resulting from the local dysymmetry of matter and antimatter, (2) external fields, (3) the decay of the \(\ce{K2^0}\) into a \(\ce{K1^0}\) with the subsequent decay of the \(\ce{K1^0}\)into two pions, which was allowed by the symmetry, (4) the emission of another neutral particle, “the paritino,” in the \(\ce{K2^0}\) decay, similar to the emission of the neutrino in beta decay, (5) that one of the pions emitted in the decay was in fact a “spion,” a pion with spin one rather than zero, (6) that the decay was due to another neutral particle, the L, produced coherently with the \(\ce{K^0}\), (7) the existence of a “shadow” universe, which interacted with out universe only through the weak interactions, and that the decay seen was the decay of the “shadow \(\ce{K2^0}\),” (8) the failure of the exponential decay law, 9) the failure of the principle of superposition in quantum mechanics, and 10) that the decay pions were not bosons.
As one can see, the limits placed on alternatives were not very stringent. By the end of 1967, all of the alternatives had been tested and found wanting, leaving CP symmetry unprotected. Here the differing judgments of the scientific community about what was worth proposing and pursuing led to a wide variety of alternatives being tested.
Hacking’s second sticking point is nominalism, or name-ism. He notes that in its most extreme form nominalism denies that there is anything in common or peculiar to objects selected by a name, such as “Douglas fir” other than that they are called Douglas fir. Opponents contend that good names, or good accounts of nature, tell us something correct about the world. This is related to the realism-antirealism debate concerning the status of unobservable entities that has plagued philosophers for millennia. For example Bas van Fraassen (1980), an antirealist, holds that we have no grounds for belief in unobservable entities such as the electron and that accepting theories about the electron means only that we believe that the things the theory says about observables is true. A realist claims that electrons really exist and that as, for example, Wilfred Sellars remarked, “to have good reason for holding a theory is ipso facto to have good reason for holding that the entities postulated by the theory exist (Sellars 1962, p. 97).” In Hacking’s view a scientific nominalist is more radical than an antirealist and is just as skeptical about fir trees as they are about electrons. A nominalist further believes that the structures we conceive of are properties of our representations of the world and not of the world itself. Hacking refers to opponents of that view as inherent structuralists.
Hacking also remarks that this point is related to the question of “scientific facts.” Thus, constructivists Latour and Woolgar originally entitled their book Laboratory Life: The Social Construction of Scientific Facts (1979). Andrew Pickering entitled his history of the quark model Constructing Quarks (Pickering 1984a). Physicists argue that this demeans their work. Steven Weinberg, a realist and a physicist, criticized Pickering’s title by noting that no mountaineer would ever name a book Constructing Everest . For Weinberg, quarks and Mount Everest have the same ontological status. They are both facts about the world. Hacking argues that constructivists do not, despite appearances, believe that facts do not exist, or that there is no such thing as reality. He cites Latour and Woolgar “that ‘out-there-ness’ is a consequence of scientific work rather than its cause (Latour and Woolgar 1986, p. 180).” Hacking reasonably concludes that,
Latour and Woolgar were surely right. We should not explain why some people believe that \(p\) by saying that \(p\) is true, or corresponds to a fact, or the facts. For example: someone believes that the universe began with what for brevity we call a big bang. A host of reasons now supports this belief. But after you have listed all the reasons, you should not add, as if it were an additional reason for believing in the big bang, ‘and it is true that the universe began with a big bang.’ Or ‘and it is a fact.’This observation has nothing peculiarly to do with social construction. It could equally have been advanced by an old-fashioned philosopher of language. It is a remark about the grammar of the verb ‘to explain’ (Hacking 1999, pp. 80–81).
One might add, however, that the reasons Hacking cites as supporting that belief are given to us by valid experimental evidence and not by the social and personal interests of scientists. Latour and Woolgar might not agree. Franklin argues that we have good reasons to believe in facts, and in the entities involved in our theories, always remembering, of course, that science is fallible.
Hacking’s third sticking point is the external explanations of stability.
The constructionist holds that explanations for the stability of scientific belief involve, at least in part, elements that are external to the content of science. These elements typically include social factors, interests, networks, or however they be described. Opponents hold that whatever be the context of discovery, the explanation of stability is internal to the science itself (Hacking 1999, p. 92). Rationalists think that most science proceeds as it does in the light of good reasons produced by research. Some bodies of knowledge become stable because of the wealth of good theoretical and experimental reasons that can be adduced for them. Constructivists think that the reasons are not decisive for the course of science. Nelson (1994) concludes that this issue will never be decided. Rationalists, at least retrospectively, can always adduce reasons that satisfy them. Constructivists, with equal ingenuity, can always find to their own satisfaction an openness where the upshot of research is settled by something other than reason. Something external. That is one way of saying we have found an irresoluble “sticking point” (pp. 91–92)
Thus, there is a rather severe disagreement on the reasons for the acceptance of experimental results. For some, like Staley, Galison and Franklin, it is because of epistemological arguments. For others, like Pickering, the reasons are utility for future practice and agreement with existing theoretical commitments. Although the history of science shows that the overthrow of a well-accepted theory leads to an enormous amount of theoretical and experimental work, proponents of this view seem to accept it as unproblematical that it is always agreement with existing theory that has more future utility. Hacking and Pickering also suggest that experimental results are accepted on the basis of the mutual adjustment of elements which includes the theory of the phenomenon.
Nevertheless, everyone seems to agree that a consensus does arise on experimental results.
Authors like Thomas Kuhn and Paul Feyerabend put forward the view that evidence does not confirm or refute a scientific theory since it is laden by it. Evidence is not a set of observational sentences autonomous from theoretical ones, as logical positivists believed. Each new theory or a theoretical paradigm, as Kuhn labeled larger theoretical frameworks, produces, as it were, evidence anew.
Thus, theoretical concepts infect the entire experimental process from the stage of design and preparation to the production and analysis of data. A simple example that is supposed to convincingly illustrate this view are measurements of temperature with a mercury thermometer one uses in order to test whether objects expand when their temperature increases. Note that in such a case one tests the hypothesis by relying on the very assumption that the expansion of mercury indicates increase in temperature.
There may be a fairly simple way out of the vicious circle in which theory and experiment are caught in this particular case of theory-ladenness. It may suffice to calibrate the mercury thermometer with a constant volume gas thermometer, for example, where its use does not rely on the tested hypothesis but on the proportionality of the pressure of the gas and its absolute temperature (Franklin et al. 1989).
Although most experiments are far more complex than this toy example, one could certainly approach the view that experimental results are theory-laden on a case-by-case basis. Yet there may be a more general problem with the view.
Bogen and Woodward (1988) argued that debate on the relationship between theory and observation overlooks a key ingredient in the production of experimental evidence, namely the experimental phenomena. The experimentalists distill experimental phenomena from raw experimental data (e.g. electronic or digital tracks in particle colliders) using various tools of statistical analysis. Thus, identification of an experimental phenomenon as significant (e.g. a peak at a particular energy of colliding beams) is free of the theory that the experiment may be designed to test (e.g. the prediction of a particular particle). Only when significant phenomenon has been identified can a stage of data analysis begin in which the phenomenon is deemed to either support or refute a theory. Thus, the theory-ladenness of evidence thesis fails at least in some experiments in physics.
The authors substantiate their argument in part through an analysis of experiments that led to a breakthrough discovery of weak neutral currents. It is a type of force produced by so-called bosons — short-lived particles responsible for energy transfer between other particles such as hadrons and leptons. The relevant peaks were recognized as significant via statistical analysis of data, and later on interpreted as evidence for the existence of the bosons.
This view and the case study have recently been challenged by Schindler (2011). He argues that the tested theory was critical in the assessment of the reliability of data in the experiments with weak neutral currents. He also points out that, on occasion, experimental data can even be ignored if they are deemed irrelevant from a theoretical perspective that physicists find particularly compelling. This was the case in experiments with so-called zebra pattern magnetic anomalies on the ocean floor. The readings of new apparatuses used to scan the ocean floor produced intriguing signals. Yet the researchers could not interpret these signals meaningfully or satisfyingly distinguish them from noise unless they relied on some theoretical account of both the structure of the ocean floor and the earth’s magnetic field.
Karaca (2013) points out that a crude theory-observation distinction is particularly unhelpful in understanding high-energy physics experiments. It fails to capture the complexity of relevant theoretical structures and their relation to experimental data. Theoretical structures can be composed of background, model, and phenomenological theories. Background theories are very general theories (e.g. quantum field theory or quantum electrodynamics) that define the general properties of physical particles and their interactions. Models are specific instances of background theories that define particular particles and their properties. While phenomenological theories develop testable predictions based on these models.
Now, each of these theoretical segments stands in a different relationship to experimental data—the experiments can be laden by a different segment to a different extent. This requires a nuanced categorization of theory-ladeness, from weak to strong.
Thus, an experimental apparatus can be designed to test a very specific theoretical model. UA1 and UA2 detectors at CERN’s Super Proton Synchrotron were designed to detect particles only in a very specific energy regime in which W and Z bosons of the Standard Model were expected to exist.
In contrast, exploratory experiments approach phenomena without relying on a particular theoretical model. Thus, sometimes a theoretical framework for an experiment consists of phenomenological theory alone. Karaca argues that experiments with deep-inelastic electron-proton scattering in the late 1960s and early 1970s are example of such weakly theory-laden experiments. The application of merely phenomenological parameters in the experiment resulted in the very important discovery of the composite rather than point-like structure of hadrons (protons and neutrons), or the so-called scaling law. And this eventually led to a successful theoretical model of the composition of hadrons, namely quantum chromodynamics, or the quark-model of strong interactions.
2. The Roles of Experiment
Although experiment often takes its importance from its relation to theory, Hacking pointed out that it often has a life of its own, independent of theory. He notes the pristine observations of Carolyn Herschel’s discovery of comets, William Herschel’s work on “radiant heat,” and Davy’s observation of the gas emitted by algae and the flaring of a taper in that gas. In none of these cases did the experimenter have any theory of the phenomenon under investigation. One may also note the nineteenth century measurements of atomic spectra and the work on the masses and properties on elementary particles during the 1960s. Both of these sequences were conducted without any guidance from theory.
In deciding what experimental investigation to pursue, scientists may very well be influenced by the equipment available and their own ability to use that equipment (McKinney 1992). Thus, when the Mann-O’Neill collaboration was doing high energy physics experiments at the Princeton-Pennsylvania Accelerator during the late 1960s, the sequence of experiments was (1) measurement of the \(\ce{K+}\) decay rates, (2) measurement of the \(\ce{K+_{e 3}}\) branching ratio and decay spectrum, (3) measurement of the \(\ce{K+_{e 2}}\) branching ratio, and (4) measurement of the form factor in \(\ce{K+_{e 3}}\) decay. These experiments were performed with basically the same experimental apparatus, but with relatively minor modifications for each particular experiment. By the end of the sequence the experimenters had become quite expert in the use of the apparatus and knowledgeable about the backgrounds and experimental problems. This allowed the group to successfully perform the technically more difficult experiments later in the sequence. We might refer to this as “instrumental loyalty” and the “recycling of expertise” (Franklin 1997b). This meshes nicely with Galison’s view of experimental traditions. Scientists, both theorists and experimentalists, tend to pursue experiments and problems in which their training and expertise can be used.
Hacking also remarks on the “noteworthy observations” on Iceland Spar by Bartholin, on diffraction by Hooke and Grimaldi, and on the dispersion of light by Newton. “Now of course Bartholin, Grimaldi, Hooke, and Newton were not mindless empiricists without an ‘idea’ in their heads. They saw what they saw because they were curious, inquisitive, reflective people. They were attempting to form theories. But in all these cases it is clear that the observations preceded any formulation of theory” (Hacking 1983, p. 156). In all of these cases we may say that these were observations waiting for, or perhaps even calling for, a theory. The discovery of any unexpected phenomenon calls for a theoretical explanation.
2.2 Confirmation and Refutation
Nevertheless several of the important roles of experiment involve its relation to theory. Experiment may confirm a theory, refute a theory, or give hints to the mathematical structure of a theory.
Let us consider first an episode in which the relation between theory and experiment was clear and straightforward. This was a “crucial” experiment, one that decided unequivocally between two competing theories, or classes of theory. The episode was that of the discovery that parity, mirror-reflection symmetry or left-right symmetry, is not conserved in the weak interactions. (For details of this episode see Franklin (1986, Ch. 1) and Appendix 1 ). Experiments showed that in the beta decay of nuclei the number of electrons emitted in the same direction as the nuclear spin was different from the number emitted opposite to the spin direction. This was a clear demonstration of parity violation in the weak interactions.
After the discovery of parity and charge conjugation nonconservation, and following a suggestion by Landau, physicists considered CP (combined parity and particle-antiparticle symmetry), which was still conserved in the experiments, as the appropriate symmetry. One consequence of this scheme, if CP were conserved, was that the \(\ce{K1^0}\) meson could decay into two pions, whereas the \(\ce{K2^0}\) meson could not. [ 10 ] Thus, observation of the decay of \(\ce{K2^0}\) into two pions would indicate CP violation. The decay was observed by a group at Princeton University. Although several alternative explanations were offered, experiments eliminated each of the alternatives leaving only CP violation as an explanation of the experimental result. (For details of this episode see Franklin (1986, Ch. 3) and Appendix 2 .)
In both of the episodes discussed previously, those of parity nonconservation and of CP violation, we saw a decision between two competing classes of theories. This episode, the discovery of Bose-Einstein condensation (BEC), illustrates the confirmation of a specific theoretical prediction 70 years after the theoretical prediction was first made. Bose (1924) and Einstein (1924; 1925) predicted that a gas of noninteracting bosonic atoms will, below a certain temperature, suddenly develop a macroscopic population in the lowest energy quantum state. [ 11 ] (For details of this episode see Appendix 3 .)
2.3 Complications
In the three episodes discussed in the previous section, the relation between experiment and theory was clear. The experiments gave unequivocal results and there was no ambiguity about what theory was predicting. None of the conclusions reached has since been questioned. Parity and CP symmetry are violated in the weak interactions and Bose-Einstein condensation is an accepted phenomenon. In the practice of science things are often more complex. Experimental results may be in conflict, or may even be incorrect. Theoretical calculations may also be in error or a correct theory may be incorrectly applied. There are even cases in which both experiment and theory are wrong. As noted earlier, science is fallible. In this section I will discuss several episodes which illustrate these complexities.
The episode of the fifth force is the case of a refutation of an hypothesis, but only after a disagreement between experimental results was resolved. The “Fifth Force” was a proposed modification of Newton’s Law of Universal Gravitation. The initial experiments gave conflicting results: one supported the existence of the Fifth Force whereas the other argued against it. After numerous repetitions of the experiment, the discord was resolved and a consensus reached that the Fifth Force did not exist. (For details of this episode see Appendix 4 .)
The Stern-Gerlach experiment was regarded as crucial at the time it was performed, but, in fact, wasn’t. [ 12 ] In the view of the physics community it decided the issue between two theories, refuting one and supporting the other. In the light of later work, however, the refutation stood, but the confirmation was questionable. In fact, the experimental result posed problems for the theory it had seemingly confirmed. A new theory was proposed and although the Stern-Gerlach result initially also posed problems for the new theory, after a modification of that new theory, the result confirmed it. In a sense, it was crucial after all. It just took some time.
The Stern-Gerlach experiment provides evidence for the existence of electron spin. These experimental results were first published in 1922, although the idea of electron spin wasn’t proposed by Goudsmit and Uhlenbeck until 1925 (1925; 1926). One might say that electron spin was discovered before it was invented. (For details of this episode see Appendix 5 ).
In the last section we saw some of the difficulty inherent in experiment-theory comparison. One is sometimes faced with the question of whether the experimental apparatus satisfies the conditions required by theory, or conversely, whether the appropriate theory is being compared to the experimental result. A case in point is the history of experiments on the double-scattering of electrons by heavy nuclei (Mott scattering) during the 1930s and the relation of these results to Dirac’s theory of the electron, an episode in which the question of whether or not the experiment satisfied the conditions of the theoretical calculation was central. Initially, experiments disagreed with Mott’s calculation, casting doubt on the underlying Dirac theory. After more than a decade of work, both experimental and theoretical, it was realized that there was a background effect in the experiments that masked the predicted effect. When the background was eliminated experiment and theory agreed. ( Appendix 6 )
Ever vaster amounts of data have been produced by particle colliders as they have grown from room-size apparata, to tens of kilometers long mega-labs. Vast numbers of background interactions that are well understood and theoretically uninteresting occur in the detector. These have to be combed in order to identify interactions of potential interest. This is especially true of hadron (proton-proton) colliders like the Large Hadron Collider (LHC), where the Higgs boson was discovered. Protons that collide in the LHC and similar hadron colliders are composed of more elementary particles, collectively labeled partons. Partons mutually interact, exponentially increasing the number of background interactions. In fact, a minuscule number of interactions are selected from the overwhelming number that occur in the detector. (In contrast, lepton collisions, such as collisions of electrons and positrons, produce much lower backgrounds, since leptons are not composed of more elementary particles.)
Thus, a successful search for new elementary particles critically depends on successfully crafting selection criteria and techniques at the stage of data collection and at the stage of data analysis. But gradual development and changes in data selection procedures in the colliders raises an important epistemological concern. The main reason for this concern is nicely anticipated by the following question, which was posed by one of the most prominent experimentalists in particle physics: “What is the extent to which we are negating the discovery potential of very-high-energy proton machines by the necessity of rejecting, a priori, the events we cannot afford to record?” (Panofsky 1994, 133). In other words, how does one decide which interactions to detect and analyze in a multitude, in order to minimize the possibility of throwing out novel and unexplored ones?
One way of searching through vast amounts of data that are already in, i.e. those that the detector has already delivered, is to look for occurrences that remain robust under varying conditions of detection. Physicists employ the technique of data cuts in such analysis. They cut out data that may be unreliable—when, for instance, a data set may be an artefact rather than a genuine particle interaction the experimenters expect. E.g. a colliding beam may interact with the walls of the detector and not with the other colliding beam, while producing a signal identical to the signal the experimenters expected the beam-beam interaction to produce. Thus, if under various data cuts a result remains stable, then it is increasingly likely to be correct and to represent the genuine phenomenon the physicists think it represents. The robustness of the result under various data cuts minimizes the possibility that the detected phenomenon only mimics the genuine one (Franklin 2013, 224–5).
At the data-acquisition stage, however, this strategy does not seem applicable. As Panofsky suggests, one does not know with certainty which of the vast number of the events in the detector may be of interest.
Yet, Karaca (2011) [ 13 ] argues that a form of robustness is in play even at the acquisition stage. This experimental approach amalgamates theoretical expectations and empirical results, as the example of the hypothesis of specific heavy particles is supposed to illustrate.
Along with the Standard Model of particle physics, a number of alternative models have been proposed. Their predictions of how elementary particles should behave often differ substantially. Yet in contrast to the Standard Model, they all share the hypothesis that there exist heavy particles that decay into particles with high transverse momentum.
Physicists apply a robustness analysis in testing this hypothesis, the argument goes. First, they check whether the apparatus can detect known particles similar to those predicted. Second, guided by the hypothesis, they establish various trigger algorithms. (The trigger algorithms, or “the triggers”, determine at what exact point in time and under which conditions a detector should record interactions. They are necessary because the frequency and the number of interactions far exceed the limited recording capacity.) And, finally, they observe whether any results remain stable across the triggers.
Yet even in this theoretical-empirical form of robustness, as Franklin (2013, 225) points out, “there is an underlying assumption that any new physics will resemble known physics”—usually a theory of the day. And one way around this problem is for physicists to produce as many alternative models as possible, including those that may even seem implausible at the time.
Perovic (2011) suggests that such a potential failure, namely to spot potentially relevant events occurring in the detector, may be also a consequence of the gradual automation of the detection process.
The early days of experimentation in particle physics, around WWII, saw the direct involvement of the experimenters in the process. Experimental particle physics was a decentralized discipline where experimenters running individual labs had full control over the triggers and analysis. The experimenters could also control the goals and the design of experiments. Fixed target accelerators, where the beam hits the detector instead of another beam, produced a number of particle interactions that was manageable for such labs. The chance of missing an anomalous event not predicted by the current theory was not a major concern in such an environment.
Yet such labs could process a comparatively small amount of data. This has gradually become an obstacle, with the advent of hadron colliders. They work at ever-higher energies and produce an ever-vaster number of background interactions. That is why the experimental process has become increasingly automated and much more indirect. Trained technicians instead of experimenters themselves at some point started to scan the recordings. Eventually, these human scanners were replaced by computers, and a full automation of detection in hadron colliders has enabled the processing of vast number of interactions. This was the first significant change in the transition from small individual labs to mega-labs.
The second significant change concerned the organization and goals of the labs. The mega-detectors and the amounts of data they produced required exponentially more staff and scientists. This in turn led to even more centralized and hierarchical labs and even longer periods of design and performance of the experiments. As a result, focusing on confirming existing dominant hypotheses rather than on exploratory particle searches was the least risky way of achieving results that would justify unprecedented investments.
Now, an indirect detection process combined with mostly confirmatory goals is conducive to overlooking of unexpected interactions. As such, it may impede potentially crucial theoretical advances stemming from missed interactions.
This possibility that physicists such as Panofsky have acknowledged is not a mere speculation. In fact, the use of semi-automated, rather than fully-automated regimes of detection turned out to be essential for a number of surprising discoveries that led to theoretical breakthroughs.
Perovic analyzes several such cases, most notably the discovery of the J/psi particle that provided the first substantial piece of evidence for the existence of the charmed quark. In the experiments, physicists were able to perform exploratory detection and visual analysis of practically individual interactions due to low number of background interactions in the linear electron-positron collider. And they could afford to do this in an energy range that the existing theory did not recognize as significant, which led to them making the discovery. None of this could have been done in the fully automated detecting regime of hadron colliders that are indispensable when dealing with an environment that contains huge numbers of background interactions.
And in some cases, such as the Fermilab experiments that aimed to discover weak neutral currents, an automated and confirmatory regime of data analysis contributed to the failure to detect particles that were readily produced in the apparatus.
The complexity of the discovery process in particle physics does not end with concerns about what exact data should be chosen out of the sea of interactions. The so-called look-elsewhere effect results in a tantalizing dilemma at the stage of data analysis.
Suppose that our theory tells us that we will find a particle in an energy range. And suppose we find a significant signal in a section of that very range. Perhaps we should keep looking elsewhere within the range to make sure it is not another particle altogether we have discovered. It may be a particle that left other undetected traces in the range that our theory does not predict, along with the trace we found. The question is to what extent we should look elsewhere before we reach a satisfying level of certainty that it is the predicted particle we have discovered.
Physicists faced such a dilemma during the search for the Higgs boson at the Large Hadron Collider at CERN (Dawid 2015).
The Higgs boson is a particle responsible for the mass of other particles. It is a scalar field that “pulls back” moving and interacting particles. This pull, which we call mass, is different for different particles. It is predicted by the Standard Model, whereas alternative models predict somewhat similar Higgs-like particles.
A prediction based on the Standard Model tells us with high probability that we will find the Higgs particle in a particular range. Yet a simple and an inevitable fact of finding it in a particular section of that range may prompt us to doubt whether we have truly found the exact particle our theory predicted. Our initial excitement may vanish when we realize that we are much more likely to find a particle of any sort—not just the predicted particle—within the entire range than in a particular section of that range. Thus, the probability of finding the Higgs anywhere within a given energy range (consisting of eighty energy ‘bins’) is much higher than the probability of finding it at a particular energy scale within that range (i.e. in any individual bin). In fact, the likelihood of us finding it in a particular bin of the range is about hundred times lower.
In other words, the fact that we will inevitably find the particle in a particular bin, not only in a particular range, decreases the certainty that it was the Higgs we found. Given this fact alone we should keep looking elsewhere for other possible traces in the range once we find a significant signal in a bin. We should not proclaim the discovery of a particle predicted by the Standard Model (or any model for that matter) too soon. But for how long should we keep looking elsewhere? And what level of certainty do we need to achieve before we proclaim discovery?
The answer boils down to the weight one gives the theory and its predictions. This is the reason the experimentalists and theoreticians had divergent views on the criterion for determining the precise point at which they could justifiably state ‘Our data indicate that we have discovered the Higgs boson’. Theoreticians were confident that a finding within the range (any of eighty bins) that was of standard reliability (of three or four sigma), coupled with the theoretical expectations that Higgs would be found, would be sufficient. In contrast, experimentalists argued that at no point of data analysis should the pertinence of the look-elsewhere effect be reduced, and the search proclaimed successful, with the help of the theoretical expectations concerning Higgs. One needs to be as careful in combing the range as one practically may. As a result, the experimentalists’ preferred value of sigmas for announcing the discovery was five. This is a standard under which very few findings have turned out to be a fluctuation in the past.
Dawid argues that a question of an appropriate statistical analysis of data is at the heart of the dispute. The reasoning of the experimentalists relied on a frequentist approach that does not specify the probability of the tested hypothesis. It actually isolates statistical analysis of data from the prior probabilities. The theoreticians, however, relied on Bayesian analysis. It starts with prior probabilities of initial assumptions and ends with the assessment of the probability of tested hypothesis based on the collected evidence. The question remains whether the experimentalists’ reasoning was fully justified. The prior expectations that the theoreticians had included in their analysis had already been empirically corroborated by previous experiments after all.
2.4 Other Roles
Experiment can also provide us with evidence for the existence of the entities involved in our theories. J.J. Thomson’s experiments on cathode rays provided grounds for belief in the existence of electrons. (For details of this episode see Appendix 7 ).
Experiment can also help to articulate a theory. Experiments on beta decay during from the 1930s to the 1950s determined the precise mathematical form of Fermi’s theory of beta decay. (For details of this episode see Appendix 8 .)
2.5 Some Thoughts on Experiment in Biology
One comment that has been made concerning the philosophy of experiment is that all of the examples are taken from physics and are therefore limited. In this section arguments will be presented that these discussions also apply to biology.
Although all of the illustrations of the epistemology of experiment come from physics, David Rudge (1998; 2001) has shown that they are also used in biology. His example is Kettlewell’s (1955; 1956; 1958) evolutionary biology experiments on the Peppered Moth, Biston betularia . The typical form of the moth has a pale speckled appearance and there are two darker forms, f. carbonaria , which is nearly black, and f. insularia , which is intermediate in color. The typical form of the moth was most prevalent in the British Isles and Europe until the middle of the nineteenth century. At that time things began to change. Increasing industrial pollution had both darkened the surfaces of trees and rocks and had also killed the lichen cover of the forests downwind of pollution sources. Coincident with these changes, naturalists had found that rare, darker forms of several moth species, in particular the Peppered Moth, had become common in areas downwind of pollution sources.
Kettlewell attempted to test a selectionist explanation of this phenomenon. E.B. Ford (1937; 1940) had suggested a two-part explanation of this effect: 1) darker moths had a superior physiology and 2) the spread of the melanic gene was confined to industrial areas because the darker color made carbonaria more conspicuous to avian predators in rural areas and less conspicuous in polluted areas. Kettlewell believed that Ford had established the superior viability of darker moths and he wanted to test the hypothesis that the darker form of the moth was less conspicuous to predators in industrial areas.
Kettlewell’s investigations consisted of three parts. In the first part he used human observers to investigate whether his proposed scoring method would be accurate in assessing the relative conspicuousness of different types of moths against different backgrounds. The tests showed that moths on “correct” backgrounds, typical on lichen covered backgrounds and dark moths on soot-blackened backgrounds were almost always judged inconspicuous, whereas moths on “incorrect” backgrounds were judged conspicuous.
The second step involved releasing birds into a cage containing all three types of moth and both soot-blackened and lichen covered pieces of bark as resting places. After some difficulties (see Rudge 1998 for details), Kettlewell found that birds prey on moths in an order of conspicuousness similar to that gauged by human observers.
The third step was to investigate whether birds preferentially prey on conspicuous moths in the wild. Kettlewell used a mark-release-recapture experiment in both a polluted environment (Birmingham) and later in an unpolluted wood. He released 630 marked male moths of all three types in an area near Birmingham, which contained predators and natural boundaries. He then recaptured the moths using two different types of trap, each containing virgin females of all three types to guard against the possibility of pheromone differences.
Kettlewell found that carbonaria was twice as likely to survive in soot-darkened environments (27.5 percent) as was typical (12.7 percent). He worried, however, that his results might be an artifact of his experimental procedures. Perhaps the traps used were more attractive to one type of moth, that one form of moth was more likely to migrate, or that one type of moth just lived longer. He eliminated the first alternative by showing that the recapture rates were the same for both types of trap. The use of natural boundaries and traps placed beyond those boundaries eliminated the second, and previous experiments had shown no differences in longevity. Further experiments in polluted environments confirmed that carbonaria was twice as likely to survive as typical. An experiment in an unpolluted environment showed that typical was three times as likely to survive as carbonaria . Kettlewell concluded that such selection was the cause of the prevalence of carbonaria in polluted environments.
Rudge also demonstrates that the strategies used by Kettlewell are those described above in the epistemology of experiment. His examples are given in Table 1. (For more details see Rudge 1998).
Table 1. Examples of epistemological strategies used by experimentalists in evolutionary biology, from H.B.D. Kettlewell’s (1955, 1956, 1958) investigations of industrial melanism. (See Rudge 1998).
The roles that experiment plays in physics are also those it plays in biology. In the previous section we have seen that Kettlewell’s experiments both test and confirm a theory. I discussed earlier a set of crucial experiments that decided between two competing classes of theories, those that conserved parity and those that did not. In this section I will discuss an experiment that decided among three competing mechanisms for the replication of DNA, the molecule now believed to be responsible for heredity. This is another crucial experiment. It strongly supported one proposed mechanism and argued against the other two. (For details of this episode see (Holmes 2001)).
In 1953 Francis Crick and James Watson proposed a three-dimensional structure for deoxyribonucleic acid (DNA) (Watson and Crick 1953a). Their proposed structure consisted of two polynucleotide chains helically wound about a common axis. This was the famous “Double Helix”. The chains were bound together by combinations of four nitrogen bases — adenine, thymine, cytosine, and guanine. Because of structural requirements only the base pairs adenine-thymine and cytosine-guanine are allowed. Each chain is thus complementary to the other. If there is an adenine base at a location in one chain there is a thymine base at the same location on the other chain, and vice versa. The same applies to cytosine and guanine. The order of the bases along a chain is not, however, restricted in any way, and it is the precise sequence of bases that carries the genetic information.
The significance of the proposed structure was not lost on Watson and Crick when they made their suggestion. They remarked, “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.”
If DNA was to play this crucial role in genetics, then there must be a mechanism for the replication of the molecule. Within a short period of time following the Watson-Crick suggestion, three different mechanisms for the replication of the DNA molecule were proposed (Delbruck and Stent 1957). These are illustrated in Figure A. The first, proposed by Gunther Stent and known as conservative replication, suggested that each of the two strands of the parent DNA molecule is replicated in new material. This yields a first generation which consists of the original parent DNA molecule and one newly-synthesized DNA molecule. The second generation will consist of the parental DNA and three new DNAs.
Figure A: Possible mechanisms for DNA replication. (Left) Conservative replication. Each of the two strands of the parent DNA is replicated to yield the unchanged parent DNA and one newly synthesized DNA. The second generation consists of one parent DNA and three new DNAs. (Center) Semiconservative replication. Each first generation DNA molecule contains one strand of the parent DNA and one newly synthesized strand. The second generation consists of two hybrid DNAs and two new DNAs. (Right) Dispersive replication. The parent chains break at intervals, and the parental segments combine with new segments to form the daughter chains. The darker segments are parental DNA and the lighter segments are newly synthesized DNA. From Lehninger (1975).
The second proposed mechanism, known as semiconservative replication is when each strand of the parental DNA acts as a template for a second newly-synthesized complementary strand, which then combines with the original strand to form a DNA molecule. This was proposed by Watson and Crick (1953b). The first generation consists of two hybrid molecules, each of which contains one strand of parental DNA and one newly synthesized strand. The second generation consists of two hybrid molecules and two totally new DNAs. The third mechanism, proposed by Max Delbruck, was dispersive replication, in which the parental DNA chains break at intervals and the parental segments combine with new segments to form the daughter strands.
In this section the experiment performed by Matthew Meselson and Franklin Stahl, which has been called “the most beautiful experiment in biology”, and which was designed to answer the question of the correct DNA replication mechanism will be discussed (Meselson and Stahl 1958). Meselson and Stahl described their proposed method. “We anticipated that a label which imparts to the DNA molecule an increased density might permit an analysis of this distribution by sedimentation techniques. To this end a method was developed for the detection of small density differences among macromolecules. By use of this method, we have observed the distribution of the heavy nitrogen isotope \(\ce{^{15}N}\) among molecules of DNA following the transfer of a uniformly \(\ce{^{15}N}\)-labeled, exponentially growing bacterial population to a growth medium containing the ordinary nitrogen isotope \(\ce{^{14}N}\)” (Meselson and Stahl 1958, pp. 671–672).
Figure B: Schematic representation of the Meselson-Stahl experiment. From Watson (1965).
The experiment is described schematically in Figure B. Meselson and Stahl placed a sample of DNA in a solution of cesium chloride. As the sample is rotated at high speed the denser material travels further away from the axis of rotation than does the less dense material. This results in a solution of cesium chloride that has increasing density as one goes further away from the axis of rotation. The DNA reaches equilibrium at the position where its density equals that of the solution. Meselson and Stahl grew E. coli bacteria in a medium that contained ammonium chloride \((\ce{NH4Cl})\) as the sole source of nitrogen. They did this for media that contained either \(\ce{^{14}N}\), ordinary nitrogen, or \(\ce{^{15}N}\), a heavier isotope. By destroying the cell membranes they could obtain samples of DNA which contained either \(\ce{^{14}N}\) or \(\ce{^{15}N}\). They first showed that they could indeed separate the two different mass molecules of DNA by centrifugation (Figure C). The separation of the two types of DNA is clear in both the photograph obtained by absorbing ultraviolet light and in the graph showing the intensity of the signal, obtained with a densitometer. In addition, the separation between the two peaks suggested that they would be able to distinguish an intermediate band composed of hybrid DNA from the heavy and light bands. These early results argued both that the experimental apparatus was working properly and that all of the results obtained were correct. It is difficult to imagine either an apparatus malfunction or a source of experimental background that could reproduce those results. This is similar, although certainly not identical, to Galileo’s observation of the moons of Jupiter or to Millikan’s measurement of the charge of the electron. In both of those episodes it was the results themselves that argued for their correctness.
Figure C: The separation of \(\ce{^{14}N}\) DNA from \(\ce{^{15}N}\) DNA by centrifugation. The band on the left is \(\ce{^{14}N}\) DNA and that on the right is from \(\ce{^{15}N}\) DNA. From Meselson and Stahl (1958).
Meselson and Stahl then produced a sample of E coli bacteria containing only \(\ce{^{15}N}\) by growing it in a medium containing only ammonium chloride with \(\ce{^{15}N}\) \((\ce{^{15}NH4Cl})\) for fourteen generations. They then abruptly changed the medium to \(\ce{^{14}N}\) by adding a tenfold excess of \(\ce{^{14}NH_4Cl}\). Samples were taken just before the addition of \(\ce{^{14}N}\) and at intervals afterward for several generations. The cell membranes were broken to release the DNA into the solution and the samples were centrifuged and ultraviolet absorption photographs taken. In addition, the photographs were scanned with a recording densitometer. The results are shown in Figure D, showing both the photographs and the densitometer traces. The figure shows that one starts only with heavy (fully-labeled) DNA. As time proceeds one sees more and more half-labeled DNA, until at one generation time only half-labeled DNA is present. “Subsequently only half labeled DNA and completely unlabeled DNA are found. When two generation times have elapsed after the addition of \(\ce{^{14}N}\) half-labeled and unlabeled DNA are present in equal amounts” (p. 676). (This is exactly what the semiconservative replication mechanism predicts). By four generations the sample consists almost entirely of unlabeled DNA. A test of the conclusion that the DNA in the intermediate density band was half labeled was provided by examination of a sample containing equal amounts of generations 0 and 1.9. If the semiconservative mechanism is correct then Generation 1.9 should have approximately equal amounts of unlabeled and half-labeled DNA, whereas Generation 0 contains only fully-labeled DNA. As one can see, there are three clear density bands and Meselson and Stahl found that the intermediate band was centered at \((50 \pm 2)\) percent of the difference between the \(\ce{^{14}N}\) and \(\ce{^{15}N}\) bands, shown in the bottom photograph (Generations 0 and 4.1). This is precisely what one would expect if that DNA were half labeled.
Figure D: (Left) Ultraviolet absorption photographs showing DNA bands from centrifugation of DNA from E. Coli sampled at various times after the addition of an excess of \(\ce{^{14}N}\) substrates to a growing \(\ce{^{15}N}\) culture. (Right) Densitometer traces of the photographs. The initial sample is all heavy (\(\ce{^{15}N}\) DNA). As time proceeds a second intermediate band begins to appear until at one generation all of the sample is of intermediate mass (Hybrid DNA). At longer times a band of light DNA appears, until at 4.1 generations the sample is almost all lighter DNA. This is exactly what is predicted by the Watson-Crick semiconservative mechanism. From Meselson and Stahl (1958)
Meselson and Stahl stated their results as follows, “The nitrogen of DNA is divided equally between two subunits which remain intact through many generations…. Following replication, each daughter molecule has received one parental subunit” (p. 676).
Meselson and Stahl also noted the implications of their work for deciding among the proposed mechanisms for DNA replication. In a section labeled “The Watson-Crick Model” they noted that, “This [the structure of the DNA molecule] suggested to Watson and Crick a definite and structurally plausible hypothesis for the duplication of the DNA molecule. According to this idea, the two chains separate, exposing the hydrogen-bonding sites of the bases. Then, in accord with base-pairing restrictions, each chain serves as a template for the synthesis of its complement. Accordingly, each daughter molecule contains one of the parental chains paired with a newly synthesized chain…. The results of the present experiment are in exact accord with the expectations of the Watson-Crick model for DNA replication” (pp. 677–678).
It also showed that the dispersive replication mechanism proposed by Delbruck, which had smaller subunits, was incorrect. “Since the apparent molecular weight of the subunits so obtained is found to be close to half that of the intact molecule, it may be further concluded that the subunits of the DNA molecule which are conserved at duplication are single, continuous structures. The scheme for DNA duplication proposed by Delbruck is thereby ruled out” (p. 681). Later work by John Cairns and others showed that the subunits of DNA were the entire single polynucleotide chains of the Watson-Crick model of DNA structure.
The Meselson-Stahl experiment is a crucial experiment in biology. It decided between three proposed mechanisms for the replication of DNA. It supported the Watson-Crick semiconservative mechanism and eliminated the conservative and dispersive mechanisms. It played a similar role in biology to that of the experiments that demonstrated the nonconservation of parity did in physics. Thus, we have seen evidence that experiment plays similar roles in both biology and physics and also that the same epistemological strategies are used in both disciplines.
One interesting recent development in science, and thus in the philosophy of science, has been the increasing use of, and importance of, computer simulations. In some fields, such as high-energy physics, simulations are an essential part of all experiments. It is fair to say that without computer simulations these experiments would be impossible. There has been a considerable literature in the philosophy of science discussing whether computer simulations are experiments, theory, or some new kind of hybrid method of doing science. But, as Eric Winsberg remarked, “We have in other words, rejected the overly conservative intuition that computer simulation is nothing but boring and straightforward theory application. But we have avoided embracing the opposite, overly grandiose intuition that simulation is a radically new kind of knowledge production, ”on a par“ with experimentation. In fact, we have seen that soberly locating simulation ”on the methodological map“ is not a simple matter (Winsberg 2010, p. 136).”
Given the importance of computer simulations in science it is essential that we have good reasons to believe their results. Eric Winsberg (2010), Wendy Parker (2008) and others have shown that scientists use strategies quite similar to those discussed in Section 1.1.1, to argue for the correctness of computer simulations.
The distinction between observation and experiment is relatively little discussed in philosophical literature, despite its continuous relevance to the scientific community and beyond in understanding specific traits and segments of the scientific process and the knowledge it produces.
Daston and her coauthors (Daston 2011; Daston and Lunbeck 2011; Daston and Galison 2007) have convincingly demonstrated that the distinction has played a role in delineating various features of scientific practice. It has helped scientists articulate their reflections on their own practice.
Observation is philosophically a loaded term, yet the epistemic status of scientific observation has evolved gradually with the advance of scientific techniques of inquiry and the scientific communities pursuing them. Daston succinctly summarizes this evolution in the following passage:
Characteristic of the emergent epistemic genre of the observations was, first, an emphasis on singular events, witnessed first hand (autopsia) by a named author (in contrast to the accumulation of anonymous data over centuries described by Cicero and Pliny as typical of observationes); second, a deliberate effort to separate observation from conjecture (in contrast to the medieval Scholastic connection of observation with the conjectural sciences, such as astrology); and third, the creation of virtual communities of observers dispersed over time and space, who communicated and pooled their observations in letters and publications (in contrast to passing them down from father to son or teacher to student as rare and precious treasures). (2011, 81)
Observation gradually became juxtaposed to other, more complex modes of inquiry such as experiment, “whose meaning shifted from the broad and heterogeneous sense of experimentum as recipe, trial, or just common experience to a concertedly artificial manipulation, often using special instruments and designed to probe hidden causes” (Daston 2011, 82).
In the 17th century, observation and experiment were seen as “an inseparable pair” (Daston 2011, 82) and by the 19th century they were understood to be essentially opposed, with the observer increasingly seen as passive and thus epistemically inferior to the experimenter. In fact, already Leibniz anticipated this view stating that “[t]here are certain experiments that would be better called observations, in which one considers rather than produces the work” (Daston 2011, 86). This aspect of the distinction has been a mainstay of understanding scientific practice ever since.
Apart from this historical analysis, there are currently two prominent and opposed views of the experiment-observation distinction. Ian Hacking has characterized it as well-defined, while avoiding the claim that observation and experiment are opposites (Hacking 1983, 173). According to him, the notions signify different things in scientific practice. The experiment is a thorough manipulation that creates a new phenomenon, and observation of the phenomenon is its outcome. If scientists can manipulate a domain of nature to such an extent that they can create a new phenomenon in a lab, a phenomenon that normally cannot be observed in nature, then they have truly observed the phenomenon (Hacking 1989, 1992).
Meanwhile, other authors concur that “the familiar distinction between observation and experiment … [is] an artefact of the disembodied, reconstructed character of retrospective accounts” (Gooding 1992, 68). The distinction “collapses” when we are faced with actual scientific practice as a process, and “Hacking’s observation versus experiment framework does not survive intact when put to the test in a range of cases of scientific experimentation” (Malik 2017, 85). First, the uses of the distinction cannot be compared across scientific fields. And second, as Gooding (1992) suggests, observation is a process too, not simply a static result of manipulation. Thus, both observation and experiment are seen as concurrent processes blended together in scientific practice.
Malik (2017, 86) states that these arguments are the reason why “very few [authors] use Hacking’s nomenclature of observation/experiment” and goes so far to conclude that “to (try to) distinguish between observation and experiment is futile.” There is no point delineating the two except perhaps in certain narrow domains; e.g., Hacking’s notion of the experiment based on creating phenomena might be useful within a narrow domain of particle physics. (See also Chang 2011.) He advocates avoiding the distinction altogether and opting for “the terminology [that] underlines this sense of continuousness” (Malik 2017, 88) instead. If we want to analyze scientific practice, the argument goes, we should leave behind the idea of the distinction as fundamental and turn to the characterization and analysis of various “epistemic activities” instead, e.g., along the lines suggested by Chang (2011).
A rather obvious danger of this approach is an over-emphasis on the continuousness of the notions of observation and experiment that results in inadvertent equivocation. And this, in turn, results in sidelining the distinction and its subtleties in the analysis of the scientific practice, despite their crucial role in articulating and developing that practice since the 17th century. This issue certainly requires further philosophical and historical analysis.
In this entry varying views on the nature of experimental results have been presented. Some argue that the acceptance of experimental results is based on epistemological arguments, whereas others base acceptance on future utility, social interests, or agreement with existing community commitments. Everyone agrees , however, that for whatever reasons, a consensus is reached on experimental results. These results then play many important roles in physics and we have examined several of these roles, although certainly not all of them. We have seen experiment deciding between two competing theories, calling for a new theory, confirming a theory, refuting a theory, providing evidence that determined the mathematical form of a theory, and providing evidence for the existence of an elementary particle involved in an accepted theory. We have also seen that experiment has a life of its own, independent of theory. If, as I believe, epistemological procedures provide grounds for reasonable belief in experimental results, then experiment can legitimately play the roles I have discussed and can provide the basis for scientific knowledge.
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- –––, 1995. “Comments on Rheinberger”, in Concepts, Theories, and Rationality in the Biological Sciences , G. Wolters, J. G. Lennox and P. McLaughlin (eds.), Pittsburgh: University of Pittsburgh Press: 123–136.
- Gooding, D., 1990. Experiment and the Making of Meaning , Dordrecht: Kluwer Academic Publishers.
- Gooding, D., T. Pinch and S. Schaffer (eds.), 1989. The Uses of Experiment , Cambridge: Cambridge University Press.
- Koertge, N. (ed.), 1998. A House Built on Sand: Exposing Postmodernist Myths About Science , Oxford: Oxford University Press.
- Pickering, A. (ed.), 1992. Science as Practice and Culture , Chicago: University of Chicago Press.
- Pinch, T., 1986. Confronting Nature , Dordrecht: Reidel.
- Rasmussen, N., 1993. “Facts, Artifacts, and Mesosomes: Practicing Epistemology with the Electron Microscope”, Studies in History and Philosophy of Science , 24: 227–265.
- Rheinberger, H.-J., 1997. Toward a History of Epistemic Things , Stanford: Stanford University Press.
- Shapere, D., 1982. “The Concept of Observation in Science and Philosophy”, Philosophy of Science , 49: 482–525.
- Weber, M., 2005. Philosophy of Experimental Biology , Cambridge: Cambridge University Press.
How to cite this entry . Preview the PDF version of this entry at the Friends of the SEP Society . Look up topics and thinkers related to this entry at the Internet Philosophy Ontology Project (InPhO). Enhanced bibliography for this entry at PhilPapers , with links to its database.
[Please contact the authors with suggestions.]
confirmation | logic: inductive | rationalism vs. empiricism | scientific method | scientific realism
Acknowledgments
We are grateful to Professor Carl Craver for both his comments on the manuscript and for his suggestions for further reading.
Copyright © 2019 by Allan Franklin < allan . franklin @ colorado . edu > Slobodan Perovic < sperovic @ f . bg . ac . rs >
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Best Physics Experiments For Kids
Rolling, bouncing, racing, zipping, squishing, and more! Physics is fun, and these simple physics experiments are perfectly fun physics for kids; you can even do them at home or with small groups in the classroom. Whether you are exploring laws of motion, sound waves, or light, physics is everywhere! Make sure to check out all of our science experiments for all year-round learning and play.
THE BEST PHYSICS PROJECTS FOR KIDS
FUN PHYSICS EXPERIMENTS
Can physics be playful? Absolutely, and we will show you AMAZING physics projects for kids that are easy to set up, budget-friendly, and of course playful! Hands-on is the way to go with our young scientists, explorers, and engineers.
From catapults to rockets and ramps to light and sound, you will find a little bit of everything to start enjoying physics at home or add to your classroom lessons with your kids. We even have some free fun printable packs to help you get started at the bottom of this page.
Oh and if you are looking for an equally awesome collection of chemistry experiments for kids , we have that too!
WHAT IS PHYSICS?
Physics is, most simply put, the study of matter and energy and the interaction between the two .
How did the Universe begin? You might not have the answer to that question! However, you can pull off these cool physics experiments to get your kids thinking, observing, questioning, and experimenting.
Let’s keep it basic for our younger scientists. Physics is all about energy and matter and the relationship they share.
Like all sciences, physics is all about solving problems and figuring out why things do what they do. Keep in mind that simple physics experiments can involve some chemistry too!
Kids are great for questioning everything, and we want to encourage…
- experimenting
- reinventing
- questioning
- critical thinking
- and more…..
In the physics experiments below, some of the things you will learn a little about are static electricity, Newton’s 3 Laws of Motion, simple machines, buoyancy, density, and more! And with easy household supplies, you can still do awesome physics projects at home on a budget!
Encourage your kids to make predictions, discuss observations, and re-test their ideas if they don’t get the desired results the first time. Science always includes an element of mystery that kids naturally love to figure out! Learn more about using the scientific method with kids here .
We have a brand new series surrounding the NGSS science standards so you can work all these great ideas into your lesson plans.
SCIENCE FAIR PROJECTS
Want to turn one of these fun and easy physics experiments into a science project? Then check out these helpful resources.
- Easy Science Fair Projects
- Science Project Tips From A Teacher
- Science Fair Board Ideas
Click here to get your FREE Physics Ideas Pack !
SIMPLE PHYSICS EXPERIMENTS FOR KIDS
You will love these neat physics project ideas we have to share with you. I handpick my selections based on what I think my son would enjoy, what supplies are needed, and what amount of time needs to be dedicated to each activity.
Click on each link for the full descriptions of each of the experiments and activities.
AIR PRESSURE CAN EXPERIMENT
Learn about atmospheric pressure with this incredible can crusher experiment.
AIR RESISTANCE EXPERIMENT
Whoa! A physics experiment in under 10 mins and all you need to do is go raid the computer printer! Make simple air foils and learn about air resistance.
AIR VORTEX CANNON
Make your own homemade air cannon and blast down dominoes and other similar items. Learn about air pressure and the movement of air particles in the process.
BALANCING APPLE EXPERIMENT
Can you balance an apple on your finger? We explored balancing apples and gravity with real apples for our Ten Apples Up On Top Dr Seuss theme and it was pretty challenging! Now let’s try to balance a paper apple (use our FREE printable template to make your own).
BALLOON CAR
There are I am sure many ways for you to come up with a balloon car. I have two balloon car design suggestions to get the creative juices flowing! You can make a LEGO balloon car or you can make a cardboard balloon car . Both work off of a similar principle and really go. Find out which makes the fastest balloon car,
BALLOON ROCKET
Explore fun forces with an easy to set up balloon rocket project. Also see our Valentine’s Day version , and we have a Santa balloon rocket too! This simple experiment can be turned into any fun theme. You can even race two balloons or set it up outside!
Pennies and foil are all you need to learn about buoyancy. Oh. and a bowl of water too!
CAPILLARY ACTION
Check out these fun ways to demonstrate capillary action. Plus, all you need is a handful of standard household supplies.
COLOR CHANGING FLOWERS
Learn about the forces of capillary action as you change your flowers from white to green. Or any color you like! Easy to set up and perfect for a group of kiddos to do simultaneously.
COLOR WHEEL SPINNER
Famous scientist, Isaac Newton discovered that light is made up of many colors. Learn more by making your spinning color wheel! Can you make white light from all the different colors?
DANCING SPRINKLES EXPERIMENT
Explore sound and vibrations when you try this fun dancing sprinkles experiment with the kids.
DENSITY TOWER EXPERIMENT
Explore how some liquids are heavier or denser than other liquids with this super easy physics experiment.
DROPS OF WATER ON A PENNY
How many drops of water can you fit on a penny? Explore surface tension of water when you try this fun penny lab with the kids.
EGG DROP PROJECT
Check out our mess-free version of a classic science experiment. This egg drop challenge is a great way to introduce kids to the scientific method as you test out ideas to protect your egg from cracking.
Let the egg race experiments begin! Which egg will roll to the bottom of the ramp first? Help your kids make predictions as to what will happen with different size eggs and different angles of ramps.
Older kids may also find learning about Newton’s 3 Laws to be interesting, and explore how they can apply those ideas to their egg races.
ELECTRIC CORNSTARCH
Can you make oobleck jump? Learn about static electricity with this fun cornstarch and oil experiment.
FLOATING PAPERCLIP EXPERIMENT
How do you make a paperclip float on water? This is an awesome physics activity for young kids and older ones too! Learn about surface tension of water, with a few simple supplies.
FLOATING RICE
Can you lift a bottle of rice with a pencil? Explore the force of friction with this easy physics experiment.
HOMEMADE COMPASS
Learn about magnets and magnetic fields with this fun and easy DIY compass project. Build your own compass that will show you which way is north.
HOW DO SHARKS FLOAT
Or why is it that sharks don’t sink in the ocean? Learn about how these great fish coast around through the ocean and buoyancy with this simple physics activity.
Check out more awesome shark week activities here.
HOW TO MAKE RAINBOWS
Explore light and refraction when you make rainbows using a variety of simple supplies—awesome hands-on science for kids of all ages.
KALEIDOSCOPE FOR KIDS
Learn how to create a kaleidoscope for simple physics.
KITE BUILDING
A good breeze and a few materials are all you need to tackle this Kite making physics project at home, with a group or in the classroom. Learn about forces needed to keep a kite up in the air, as you fly your own kite.
Explore physics with common items found around the house. A homemade lava lamp (or density experiment) is one of our favorite science experiments for kids.
LEGO PARACHUTE
If your mini-figure was about to go skydiving, would they have a LEGO® Parachute? And would their parachute actually work and carry them safely to the ground? Experiment with different materials to see what makes a good parachute.
LEGO ZIP LINE
Can you set up a LEGO zip line and see how well it holds up when in motion? This LEGO® building challenge is also a great way to introduce gravity, friction, slope, energy, and motion while getting creative with your LEGO® design. You could also add a pulley mechanism like we did here for this toy zip line .
LEMON BATTERY
What can you power with a lemon battery? Grab some lemons and a few other supplies, and find out how you can make lemons into lemon electricity!
MAGNET DISCOVERY TABLE
Explore magnets with these simple discovery table ideas. Magnets are fascinating science and kids love to play with them!
YOU MAY ALSO LIKE: Magnet Painting
MAGNIFYING GLASS
Here’s how you can make your own homemade magnifying glass from a plastic bottle and a drop of water. Find out how a magnifying glass works with some simple physics.
MARBLE RUN WALL
Pool noodles are amazing and cheap materials for so many STEM projects. I keep a bunch on hand all year-long to keep my kid busy. I bet you didn’t know how useful a pool noodle could be for physics projects. Learn about gravity, friction, energy and more with hands-on physics fun!
YOU MAY ALSO LIKE: Cardboard Tube Marble Run
MARBLE VISCOSITY EXPERIMENT
Grab some marbles and find out which one will fall to the bottom first with this easy viscosity experiment.
PAPER CLIP EXPERIMENT
All you need is a glass of water and paper clips for this simple physics experiment that explores surface tension.
PADDLE BOAT DIY
Learn about kinetic and potential energy with this simple paddle boat project.
PAPER HELICOPTER
Make a paper helicopter that actually flies! This is an awesome physics challenge for young kids and older ones too. Learn about what helps helicopters rise into the air, with a few simple supplies.
POPSICLE STICK CATAPULT
Want to learn how to make a catapult with popsicle sticks? This Popsicle stick catapult design is an easy physics experiment for kids of all ages! Everyone loves to launch stuff into the air.
We have also made a spoon catapult , LEGO catapult , pencil catapult , and a jumbo marshmallow catapult !
LEGO RUBBER BAND CAR
We made a simple LEGO rubber band car to go along with our favorite superhero book. Again these can be made as simple or as detailed as your kids would like to make them, and it’s all STEM!
PENNY SPINNER
Make these fun paper spinner toys out of simple household materials. Kids love things that spin and spinning tops are one of the earliest toys made in the US.
POM POM SHOOTER
Similar to our snowball launcher further on, but this physics activity uses a toilet paper tube and balloon to launch pom poms. How far can you fling them? See Newton’s Laws of Motion in action!
POP ROCKS EXPERIMENT
We tested a variety of fluids all with a unique viscosity for this fun pop rocks science experiment. Grab a few packs of pop rocks and don’t forget to taste them too!
RAINBOW IN A JAR
This water density experiment with sugar uses only a few kitchen ingredients but produces an amazing physics project for kids! Enjoy finding out about the basics of color mixing all the way up to the density of liquids.
RISING WATER EXPERIMENT
Add a burning candle to a tray of water, cover it with a jar and watch what happens!
ROLLING PUMPKINS
It doesn’t get much easier than pumpkin rolling on homemade ramps. And what makes it even better is that it’s also a great simple physics experiment for kids.
RUBBER BAND CAR
Kids love building things that move! Plus, it’s even more fun if you can make a car go without just pushing it or by adding an expensive motor.
SALT WATER DENSITY EXPERIMENT
This easy to set up salt water density experiment is a cool variation of the classic sink or float experiment. What will happen to the egg in salt water? Will an egg float or sink in salty water? There are so many questions to ask and predictions to make with this easy physics experiment for kids.
SCREAMING BALLOON EXPERIMENT
This screaming balloon experiment is an awesome physics activity for young kids and older ones too! Explore centripetal force or how objects travel a circular path.
SHADOW PUPPETS
Kids love their shadows, love to chase shadows, and love to make shadows do silly things! There’s also some fun things to learn about shadows for physics. Make simple animal shadow puppets and learn about the science of shadows.
SIMPLE PULLEY EXPERIMENT
Kids love pulleys and our homemade pulley system is sure to be a permanent fixture in your backyard this season. Make a pulley simple machine, learn a little physics, and find new ways to play.
We also have this simple pulley system you can make with a paper cup and thread.
SINK OR FLOAT
Use items straight out of the kitchen for our sink or float experiment. Plus I am sure your child will be able to come with other fun things to test! This is a simple physics experiment and totally engaging for young kids.
SNOWBALL LAUNCHER
Explore Newton’s Laws of Motion with this easy-to-make indoor snowball launcher. All you need are a few simple supplies for hands-on fun!
SOUND EXPERIMENT
Kids love to make noises and sounds is all a part of the physical sciences. This homemade xylophone sound experiment is truly a simple physics experiment for kids. So easy to set up, it’s kitchen science at it’s finest with plenty of room to explore and play!
SPECTROSCOPE
Create your own DIY spectroscope from a few simple supplies and make a rainbow from visible light for a fun physics project for kids.
STATIC ELECTRICITY
Balloons are a must for this one! This simple experiment explores the fun physics that kids love. I bet you’ve even tried it yourself. Although it’s themed for Valentine’s Day, you can make it your own!
BROKEN TOOTHPICK
Is it magic or is it science? Make a star out of broken toothpicks by only adding water, and see capillary action at work.
VISCOSITY EXPERIMENT
Test the viscosity or “thickness” of different household liquids with this easy physics experiment for kids.
WATER DISPLACEMENT EXPERIMENT
Learn about water displacement and what it measures with this simple physics experiment for kids.
VALENTINE PHYSICS EXPERIMENTS
5 simple physics experiments with a Valentine’s Day theme, including a balloon rocket, static electricity, buoyancy, and more!
SIMPLE PHYSICS EXPERIMENTS MAKE LEARNING A BLAST!
Make sure to bookmark all of our resources to make your science and STEM planning a breeze.
MORE FUN SCIENCE ACTIVITIES FOR KIDS
- CHEMICAL REACTION EXPERIMENTS
- SIMPLE ENGINEERING PROJECTS FOR KIDS
- WATER EXPERIMENTS
- SELF PROPELLED VEHICLES
- EDIBLE SCIENCE EXPERIMENTS
- CHEMISTRY EXPERIMENTS FOR KIDS
Wow, I see so many ideas here I want to try? Gravity art, nuts and bolts sculptures…my daughter is going to love these!
Great list of activities! I know that even as an engineer, physics “sounds” hard. Anything we can do to get kids trying it, playing with it and learning it helps remove that stigma. Thanks for including our slime, too 🙂
Your welcome! Yes Physics does sound intimidating but it doesn’t have to be.
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- Pingback: Scientific Method For Kids with Examples | Little Bins for Little Hands
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50 Awesome Physics Science Experiments for Middle School
August 1, 2022 // by Carly Gerson
Physics is a subject that can be difficult for students to understand. With complex equations and situations, students often struggle to visualize what the problem actually means. Experiments and activities are an excellent way for students to create a simulation of what the problem looks like in real life. Not only do experiments and activities help students better understand the situation, but also create an interactive way to engage students.
Read on to learn about fun and educational experiments!
1. Newton's Cradle
Newton's Cradle is a classic physics experiment that uses basic materials to demonstrate kinetic energy and potential energy . Students will love watching after the initial drop how the marble causes the other marbles to move. This is a great way to demonstrate the basic concept of energy transfer in an engaging way.
Learn More: 123 Homeschool 4 Me
2. Simple Bernoulli Experiment
The Bernoulli experiment is an excellent way to teach students about pressure in the air. This is also a great experiment for teachers with limited materials. Students will use construction paper, tape, a bendy straw, a ping pong ball, scissors, and a pencil to demonstrate how large vehicles like planes can stay high in the air. This abstract concept will be brought to life quickly!
3. Car Science Experiment for Air Resistance and Mass
One physics concept that will be fun to teach your students is the impact of mass on motion. Your students will feel like modern physicists as they place cars with different masses on their race track. While it may seem like a simple experiment, students can complete many trials to find an average time to go down the track based on mass.
Learn More: Frugal Fun 4 Boys
4. Archimedes' Screw Simple Machine
This fun project is a great way for school students to learn about moving liquids, in particular water. Archimedes' Screw is a commonly known machine that moves water upward and transfers it from one place to another. Kids will love watching as the liquid moves through their homemade creations.
5. Layering Liquids Density Experiment
Children will love participating in this tasty and colorful activity. Have students use different colored juices or beverages to test out the density of each one. Everyone will watch in amazement as the different colored liquids float to different places. This experiment requires the basic supplies of a beaker and different types of liquids.
Learn More: Inspiration Laboratories
6. Launching Easter Eggs Experiment
This activity would make for an incredibly fun science fair project or a great science activity during the Easter season. Using a mini catapult and plastic eggs, students will test how mass impacts the distance traveled by the egg. This experiment will definitely make your students smile!
7. Balloon in a Bottle Properties of Air Experiment
Balloon science is a fantastic way to engage your students in physics learning! Students will follow along in amazement as the balloon is inflated inside of the plastic bottle. By changing the properties of the bottle, students will learn about how air moves and is transferred.
Learn More: Steve Spangler Science
8. Elephant Toothpaste
Elephant toothpaste is a viral science experiment that is taking over the internet. Students will enjoy this explosive science experiment that combines dish soap, hydrogen peroxide, and a few other ingredients to make this silly-looking creation.
Learn More: Teach Beside Me
9. How to Make a Pendulum Wave
This physics science project is both fun to make and incredible to look at! Using washers and a few other simple materials, students will stare at their experiment for hours on end. Besides being mesmerizing, students will learn about waves and motion.
Learn More: NightHawkInLight
10. Creating Catapults
A homemade catapult is a great way to use cheap materials in a science experiment. Have students use household materials to determine which combination makes for the best catapult.
Learn More: Science Gal
11. Inertia Tower Activity
This creative activity uses sheets of paper or index cards to separate a tower of cups. The object of this activity is to remove the papers without disturbing the rest of the tower. Students will love this engineering project.
Learn More: Perkin's E-Learning
12. Marshmallow Catapult
This marshmallow catapult is a great way to test out your students' engineering skills. Using materials like a tissue box and pencil, students will have so much fun trying out different sizes and shapes of marshmallows to see which one goes the furthest.
Learn More: Random Scraps
13. Rice Friction Experiment
Friction can be a challenging concept to teach middle school students. Your students will love getting a better understanding through this simple science experiment. Using a plastic bottle, funnel, chopstick, and rice, students will learn how to increase and decrease friction.
Learn More: Carrots Are Orange
14. Balancing Robot
Add arts and crafts to physics class in this fun and adorable activity. Students will learn about balance and distribution of mass. You can even have your students color their robots and then compete!
Learn More: Buggy and Buddy
15. Heat Energy Ice Cream Lab Activity
Students will be their own heat source in this delicious science experiment. Have students learn about heat transfer and the reaction between the liquid and salt. Once students are done learning, this tasty experiment will be a hit!
Learn More: Delish
16. Gravity and Free-Fall Inquiry Lab
Students can use one of their favorite childhood books to learn about the concept of gravity. Using a stuffed moose and a muffin, students can learn about how mass and other factors impact gravity and the speed of falling.
Learn More: The Trendy Science Teacher
17. Color Mixing Tray Experiment
Students can learn all about color and how light transforms color in this interactive activity. Afterward, students can create their own color wheel!
18. How to Make Corncob Popcorn
For science teachers looking to better engage their students, look no further than this tasty activity. Students will learn about pressure and how heat impacts the corn kernels and make delicious popcorn!
Learn More: Tinker Lab
19. Skittles Density Rainbow
Using a different quantity of Skittles in each liquid, students will learn about how solids impact the density of liquids. This is a cool science experiment your students will ask to do again and again.
Learn More: Gift Of Curiosity
20. Mini Wave Model
This more complex activity will be one that your students will want to bring home and show their families. Since this activity uses a drill and hot glue, adult supervision is incredibly important.
Learn More: Instructables
21. Dancing Raisins Science Experiment
Students will love this fun science experiment as they watch the carbonation of the soda water lift the raisins and "make them dance". Students will also learn about density.
22. Learning With Dry Ice
Using dry ice is a great way to teach students about how clouds are formed. Inspire future meteorologists in this visually appealing experiment.
Learn More: Penguin Dry Ice
23. Sink or Float Experiment
If you are looking for experiments with water that will keep kids cool and entertained on a hot day, try out this food floating activity. Students will use different fruits and vegetables to see if it floats on water or sinks to the bottom.
Learn More: KC Edventures
24. Learning About Arches
Students can learn about how heavy-weight objects such as cars on a bridge are supported through arches. This activity will have students test out different types of arches to see which one holds the most weight.
Learn More: Imagine Childhood
25. Heat Changing Colored Slime
This unique experiment requires very specific materials, but when purchased will lead to a really cool science experiment. Students will love learning about thermodynamics and how heat can change the color of certain materials.
Learn More: Left Brain Craft Brain
26. Homemade Marble Run
Using household materials, create a track for marbles using only objects your kids find in the house or in the classroom. This activity can also be done by purchasing PVC pipes or other more traditional track materials. Your kids will love testing out different types of marble runs and seeing how it impacts the time it takes the marble to complete it.
27. Candy Bar Sink or Float Activity
Students can use their favorite tasty treats to make predictions on whether their candy will sink or float. This would be a great activity to complete at home or in the classroom during the Halloween season.
Learn More: Reading Confetti
28. Ice Hockey Puck Friction Experiment
In this activity, students will use different flat circular items like bottle caps and coins to determine which materials make the best ice hockey puck. This activity will help students learn about friction. This is a great experiment for an icy winter day.
Learn More: Science Sparks
29. Transfer of Momentum Basketball Activity
For a quick science activity during recess or on a sunny day, have students use different-sized balls to learn about momentum. Students will have so much fun playing and learning at the same time.
Learn more: Frugal Fun 4 Boys
30. Pumpkin Boats
Have students learn about buoyancy and density in this fun pumpkin challenge. Students can make different-sized pumpkin boats and then make predictions about whether or not their pumpkin boat will sink or float.
Learn More: The Preschool Toolbox
31. Air Resistance Experiment
Using differently sized and types of pieces of paper, students will learn about air resistance as they drop the different pieces of paper from high up and watch them fall. Have students time how long their paper took to hit the ground and what they learned about air resistance.
Learn More: Little Bins For Little Hands
32. Growing Pumpkins Inside of Pumpkins
While this is more of a biology and ecology activity, students of all ages will love learning about nature and caring for their very own pumpkin. Students can experiment in different growing conditions and track the time it takes for the pumpkins to grow.
Learn More: Life With Moore Babies
33. How to Make a Hovercraft
Using simple household materials, students can learn about air resistance in this unique craft. Students will love creating their very own hovercraft that they can take home and practice what they learned at school back at home.
34. Forces and Motion Worksheet
Determine your students' level of understanding of force and motion with this worksheet. You can use this as a pre or post-unit assessment to see what your students already understand and what they still need to learn.
Learn More: Teach Junkie
35. St. Patrick's Day Balloon Rockets
This holiday-themed activity is a great way to teach students about air resistance and acceleration. Kids will attach their balloons to a track on a string and let go to watch their balloons quickly move along the track.
Learn More: Housing A Forest
36. Marshmallow Shooter
Your students will love this silly activity that incorporates a favorite sweet treat and a unique contraption. The marshmallow will go flying through the air and students will notice how the force of the pull impacts the motion of the marshmallow.
Learn More: Teky Teach
37. Gravity and Magnetism Science Experiment
This exciting activity will have your students wanting to learn more about magnetism and how it works! Simply use a large magnet and paper clips to demonstrate how magnetism counteracts gravity.
Learn More: Rookie Parenting
38. Magic Toothpick Star Experiment
Students will watch in awe as this science experiment seems to create magic. With simple materials like toothpicks and water, students will learn about the properties of liquids and how they impact solids.
Learn More: Living Life And Learning
39. Water Powered Bottle Rocket
Bottle rockets are a fun science experiment to bring the science classroom outdoors . Students will love learning about pressure and how it impacts the velocity of an item. You can even have your students decorate their own rockets!
40. Surface Tension Experiment
Surface tension is a unique concept that students will experience in their life. Using dish soap and pepper, students will watch as the pepper seems to magically move away from them.
41. Magnetic Levitation Activity
For another magical seeming activity, attach some magnets to a surface. Then poke a pencil (or another object) through the circular magnets. Your students will be amazed as they watch the power of magnetism making your pencil seemingly float!
Learn More: Arvin D. Gupta Toys
42. Friction Ramp
Students can learn all about friction between different objects in this easy-to-set-up experiment. Have students make equal-sized "cars" made of different materials. Then students will watch as they see which cars move and which ones fail to budge.
Learn More: Teaching Ideas
43. Walking on Eggs
Students will love this seemingly sneaky activity where they walk on a carton filled with eggs. Your students can make predictions as to why the eggs don't break and reflect on their knowledge of arches.
Learn More: Playdough To Plato
44. Rubber Band Powered Car
This adorable craft will teach your students about force and how when force is applied, there is motion. Students can also try to see which rubber band car will move the farthest and go the fastest.
45. Making a Water Wheel
An at-home or in-classroom water wheel is a great activity to replicate how water powers vehicles and creates power. Your students will love seeing how their creations allow for movement to occur.
Learn More: Deceptively Educational
46. DIY Pulley Physics
This pulley system will show your students that simple machines aren't always so simple. Using whatever materials your students can find and some string, they can create intricate pulley systems along your classroom walls. This would make a great display for the entire school year.
Learn More: The Homeschool Scientist
47. How to Make an Orange Sink or Swim
Your students will watch in awe as they learn that they can change the density and buoyancy of an object by slightly altering the object. All you will need is an orange, a jar, and some water! This is an easy experiment to have all of your students partake in.
Learn More: Woo Jr.
48. Paper Airplane Test
Paper airplanes have been around for a very long time! Your students can test out different designs to see which shape of the paper airplane will fly the furthest and which shape will stay in the air the longest. The designs can include different materials as well as differently folded airplanes. This activity would make for a great classroom competition!
Learn More: Feels Like Home
49. Rising Water Experiment
Water experiments in the classroom can be so much fun! This activity will teach your students how fire can impact water and make it rise. Your students will love watching what seems like magic! Since this activity includes fire, it requires close adult supervision.
50. Physics Mystery Bag Challenge
This unique physics activity has students work in groups to solve a physics mystery. Each group of students receives the same bag of mystery items and is told what type of machine they need to create. The challenge is that there are no instructions. Using the items, students will compete to see which group creates the best of the designated machine.
Learn More: Teaching Highschool Math
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How to Do DIY Physics Experiments That Will Impress Everyone
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Science experiments are a great way to introduce kids, or the kid in all of us, to fundamental scientific principles . Here are some cool physics projects that you can do at home.
For any of these experiments, it's a good idea for an adult to supervise children, to always wear safety glasses, and if working with fire, to have a fire extinguisher handy.
Amaze Your Friends With a Fireproof Balloon
For this experiment, all you need is a balloon and a candle. Fill the balloon three-quarters full with water, and top it off with air by blowing the balloon up as far as it will go. Tie it off.
Light the candle, then slowly lower the balloon over it. Behold, the balloon won't pop!
This is due to water's incredible ability to absorb heat . The water in the balloon disperses the heat generated by the candle, and keeps the latex of the balloon from getting hot enough to break. But, when the water in the balloon can't absorb any more heat from the candle, the balloon will burst, and you'll probably get a little wet.
The Lava Lamp
From your kitchen, grab a bottle of vegetable oil, food coloring, some salt, and either a large glass or a glass jar.
Fill the glass container 2/3rds full of water and fill the remainder with vegetable oil. Add some food coloring, then slowly pour one teaspoon of salt into the container. Watch as beautiful colored orbs of oil gently fall to the bottom of the container.
At first, the oil will stay at the top of the container because oil is lighter than water . The key to making the oil fall to the bottom is the salt, it binds to the oil, making it heavier than the water. However, once the salt dissolves in the water, the oil will rise again to the top of the container. Groovy!
Grow Some Crystals
This classic experiment takes few days to complete, but it's well worth the wait.
You'll need some distilled water, salt or Epsom salts, a piece of wire or a pipe cleaner, and a glass container. First, heat the distilled water to a point just below boiling. Fill the glass container at least half full with the hot water. Add enough salt or Epsom salts to the water to create a saturated solution (the point when no more salt will dissolve in the water) and stir well.
Make a loop in the wire or pipe cleaner and lower the wire into the mixture. Place the container in a warm spot and wait. After a few days, you should see spectacular crystals forming on the loop of the wire.
This experiment works because of the temperature change of the water , and the solubility , the capability of the salt to be dissolved. As the water cools, the solubility of the solution decreases, and the salt precipitates out of the solution and onto the wire to form crystals.
Build a Popsicle Stick Catapult
To build this mini-catapult, you'll need at least 10 large popsicle sticks, a bunch of rubber bands, a pair of scissors, and some marshmallows for cannonballs. Marshmallows for cannonballs? How dastardly!
Stack eight popsicle sticks, and hold them together with rubber bands at each end. On the two remaining sticks, use the scissors to make a small notch on each side of the stick. Place them together and use a rubber band to hold the sticks together at the notch.
Then, pull the two sticks slightly apart and slide the eight-stick bundle between them. Steady your new catapult with one hand, and use your other hand to place a marshmallow on the top stick. Pull it back and release to fire!
You can also bind a plastic spoon with a rubber band to the top stick to make a bucket for holding your cannonballs. The castle walls will fall!
Make a Prism
You can make a rudimentary prism with just distilled water and clear gelatin. Empty a packet of gelatin into a pot and add only half the amount of water listed in the gelatin package instructions.
Place the pot on the stove, and as the pot warms, stir the gelatin gently to dissolve it. After the gelatin has dissolved , place the mixture into a small container and let it sit for 30 minutes to cool.
Cut the gelatin into squares or prism shapes, which is half of a square or rectangle cut on the diagonal. Shine a flashlight through the gelatin to see the light broken up into its spectral colors . You can also shine a laser pointer through the gelatin to see the light bend.
Create a Whirlpool
You can make a cool whirlpool by using two empty 2-liter soda bottles, a metal washer that has an opening smaller than the mouths of the bottles, and duct tape. Fill one of the 2-liter bottles, 2/3 full of water.
Place the washer on top of the filled bottle, and place the empty bottle upside down on top of the washer. Tape the two bottles together and quickly flip the bottles. You should see a water vortex (aka whirlpool) form as the water from the top bottle flows into the bottom bottle.
The vortex forms because the water spins faster around the edges of the bottle, creating a hole in the middle. This vacuum then fills with air from the bottom bottle, and water from the top bottle flows around it.
Build a Potato Battery
For this experiment, you'll need a potato, a galvanized nail, a piece of copper sheeting, or a copper coin such as a penny, two alligator clip leads with clips on both ends, and a voltmeter .
Galvanized nails have a zinc coating, and they can be purchased at any hardware or home improvement store. Be sure to use a fresh potato because the experiment depends on the liquid inside the potato.
Stick the galvanized nail into the potato, making sure that it doesn't go all the way through. About an inch (2.5 cm) away from the nail, stick in the penny.
Connect the penny to the red lead of the voltmeter using one of the alligator clips. Most voltmeters have red and black leads, but if your voltmeter has yellow and black leads, connect the penny to the yellow lead.
Connect the galvanized nail to the black lead of the voltmeter, and make sure both alligator clips are securely attached. Your voltmeter should show a positive reading. If it shows a negative value, simply switch the leads. You've produced electricity from a potato!
Construct a Balloon Hovercraft
You can make a small hovercraft that can slide along floors and tables by putting friction and Newton's Third Law of Motion into action. You'll need a balloon, the cap from a one or two-liter plastic soda bottle, a CD or DVD that you no longer use, an etching knife or scissors, and a glue gun.
First, create a nozzle by using the etching knife or scissors to create a hole in the bottle cap about the width of a drinking straw. Place glue all around the rim of the bottle cap, and attach it to the center of the CD or DVD. Wait for the glue to dry then check to see if has made a good seal with the CD or DVD, reapply glue if needed.
Blow up the balloon and pinch off the opening with your fingers then wrap the opening of the balloon around the nozzle of your hovercraft. Place the hovercraft on a flat surface and watch it go!
The Egg in a Bottle
This "oldie but goodie" experiment shows the relationship between atmospheric pressure and temperature. You'll need a couple of boiled and peeled eggs and a glass bottle or jar that has an opening that is somewhat smaller than the diameter of the boiled eggs. You'll also need a small piece of paper and a source of fire, such as a match or lighter. Parents should help kids with this one.
Place the glass container on a table and fold the paper into a strip that will fit inside the glass container. Light one end of the paper strip and drop the burning paper into the container. Next, set the egg on top of the opening of the glass container, and wait.
As if by magic, the egg will be sucked slowly into the bottle. This happens because the burning paper has changed the air pressure within the bottle. Soon after the egg is placed on top of the container, the fire will be extinguished, and the air inside the container will start to cool and contract. This lowers the air pressure within the container, so that the pressure in the container is lower than the air pressure outside the container. Because a ir flows from a high-pressure system to a low-pressure system, t he higher outside pressure pushes the egg into the bottle.
You can do all these experiments at home with kids, and they are a wonderful introduction into the worlds of science and engineering.
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Will the future of humanity in space involve rotating habitats or planetary settlements?
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Top 10 Beautiful Physics Experiments
The list below shows the top 10 most frequently mentioned experiments by readers of Physics World .
Top 10 beautiful experiments:
- Young's double-slit experiment applied to the interference of single electrons
- Galileo's experiment on falling bodies (1600s)
- Millikan's oil-drop experiment (1910s)
- Newton's decomposition of sunlight with a prism (1665-1666)
- Young's light-interference experiment (1801)
- Cavendish's torsion-bar experiment (1798)
- Eratosthenes' measurement of the Earth's circumference (3rd century BC)
- Galileo's experiments with rolling balls down inclined planes (1600s)
- Rutherford's discovery of the nucleus (1911)
- Foucault's pendulum (1851)
Others experiments that were cited included:
- Archimedes' experiment on hydrostatics
- Roemer's observations of the speed of light
- Joule's paddle-wheel heat experiments
- Reynolds's pipe flow experiment
- Mach & Salcher's acoustic shock wave
- Michelson-Morley measurement of the null effect of the ether
- Röntgen's detection of Maxwell's displacement current
- Oersted's discovery of electromagnetism
- The Braggs' X-ray diffraction of salt crystals
- Eddington's measurement of the bending of starlight
- Stern-Gerlach demonstration of space quantization
- Schrödinger's cat thought experiment
- Trinity test of nuclear chain reaction
- Wu et al.'s measurement of parity violation
- Goldhaber's study of neutrino helicity
- Feynman dipping an O-ring in water
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by Chris Woodford . Last updated: January 6, 2023.
Photo: There are always new theories to test and experiments to try. Even when we've completely nailed how Earth works, there's still the rest of the Universe to explore! Fourier telescope experiment photo by courtesy of NASA .
1: Galileo demonstrates that objects fall at the same speed (1589)
Photo: Galileo proved that different things fall at the same speed.
2: Isaac Newton splits white light into colors (1672)
Artwork: A glass prism splits white light into a spectrum. Nature recreates Newton's famous experiment whenever you see a rainbow!
3: Henry Cavendish weighs the world (1798)
Artwork: Henry Cavendish's experiment seen from above. 1) Two small balls, connected by a stick, are suspended by a thread so they're free to rotate. 2) The balls are attracted by two much larger (more massive) balls, fixed in place. 3) A light beam shines from the side at a mirror (green), mounted so it moves with the small balls. The beam is reflected back onto a measuring scale. 4) As the two sets of balls attract, the mirror pivots, shifting the reflected beam along the scale, so allowing the movement to be measured.
4: Thomas Young proves light is a wave... or does he? (1803)
Artwork: Thomas Young's famous double-slit experiment proved that light behaved like a wave—at least, some of the time. Left: A laser (1) produces coherent (regular, in-step) light (2) that passes through a pair of slits (3) onto a screen (4). If Newton were completely correct, we'd expect to see a single bright area on the screen and darkness either side. What we actually see is shown on the right. Light appears to ripple out in waves from the two slits (5), producing a distinctive interference pattern of light and dark areas (6).
5: James Prescott Joule demonstrates the conservation of energy (1840)
Artwork: The "Mechanical Equivalent of Heat"—James Prescott Joule's famous experiment proving the law now known as the conservation of energy.
6: Hippolyte Fizeau measures the speed of light (1851)
Artwork: How Fizeau measured the speed of light.
7: Robert Millikan measures the charge on the electron (1909)
Artwork: How Millikan measured the charge on the electron. 1) Oil drops (yellow) are squirted into the experimental apparatus, which has a large positive plate (blue) on top and a large negative plate (red) beneath. 2) X rays (green) are fired in. 3) The X rays give the oil drops a negative electrical charge. 4) The negatively charged drops can be made to "float" in between the two plates so their weight (red) is exactly balanced by the upward electrical pull of the positive plate (blue). When these two forces are equal, we can easily calculate the charge on the drops, which is always a whole number multiple of the basic charge on the electron.
8: Ernest Rutherford (and associates) split the atom (1897–1932)
Artwork: Transmutation: When Rutherford fired alpha particles (helium nuclei) at nitrogen, he produced oxygen. As he later wrote: "We must conclude that the nitrogen atom is disintegrated under the intense forces developed in a close collision with a swift alpha particle, and that the hydrogen atom which is liberated formed a constituent part of the nitrogen nucleus." In other words, he had split one atom apart to make another one.
Artwork: In Rutherford's gold-foil experiment (also known as the Geiger-Marsden experiment), atoms in a sheet of gold foil (1) allow positively charged alpha particles to pass through them (2) as long as the particles are traveling clear of the nucleus. Any particles fired at the nucleus are deflected by its positive charge (3). Fired at exactly the right angle, they will bounce right back! While this experiment is not splitting any atoms, as such, it was a key part of the decades-long effort to understand what atoms are made of—and in that sense, it did help physicists to "split" (venture inside) the atom.
9: Enrico Fermi demonstrates the nuclear chain reaction (1942)
Artwork: The nuclear chain reaction that turns uranium-235 into uranium-236 with a huge release of energy.
10: Rosalind Franklin photographs DNA with X rays (1953)
Artwork: The double-helix structure of DNA. Photographed with X rays, these intertwined curves appear as an X shape. Studying the X pattern in one of Franklin's photos was an important clue that tipped off Crick and Watson about the double helix.
If you liked this article...
Find out more, on this website.
- Six Easy Pieces by Richard Feynman. Basic Books, 2011. This book isn't half as "easy" as the title suggests, but it does contain interesting introductions to some of the topics covered here, including the conservation of energy, the double-slit experiment, and quantum theory.
- The Oxford Handbook of the History of Physics by Jed Z. Buchwald and Robert Fox (eds). Oxford University Press, 2013/2017. A collection of twenty nine scholarly essays charting the history of physics from Galileo's gravity to the age of silicon chips.
- Great Experiments in Physics: Firsthand Accounts from Galileo to Einstein Edited by Maurice Shamos. Dover, 1959/1987. This is one of my favorite science books, ever. It's a great compilation of some classic physics experiments (including four of those listed here—the experiments by Henry Cavendish, Thomas Young, James Joule, and Robert Millikan) written by the experimenters themselves. A rare opportunity to read firsthand accounts of first-rate science!
Text copyright © Chris Woodford 2012, 2023. All rights reserved. Full copyright notice and terms of use .
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