Hundreds of thousands of physical experiments were supplied for the ancient history of science. It is difficult to select a few “most-most.
Among physicists, the United States and Western Europe were surveyed. Researchers Robert Creese and Stony Beech asked them to name the most beautiful in the history of physical experiments. On the experiments included in the top ten based on a sample survey of Crisa and Buka, told Scientist Laboratory for High Energy Neutrino Astrophysics, Ph.D. in Physics and Mathematics Igor Sokalski.
1. The experiment of Eratosthenes Kirenskogo
One of the oldest known physical experiments, which measured the radius of the Earth, was held in the III century BC, the librarian of the famous Library of Alexandria Erastofenom Kirensk. Scheme of the experiment is simple. At noon, the summer solstice, in the city of Siena (now Aswan), the sun was at its zenith and the objects do not cast shadows. On the same day and at the same time in the city of Alexandria is located 800 kilometers from Siena, Sun deviated from the zenith by about 7 °. This is about 1 / 50 full circle (360 °), whence it turns out that the circle of the Earth is 40,000 kilometers, and the radius of 6300 kilometers. Seems almost incredible that such a simple method measured the radius of the Earth was only 5% less than the value obtained the most accurate modern methods, the website of “Chemistry and Life”.
2. Experiment Galileo
In the XVII century the dominant view of Aristotle, who taught that the speed of a falling body depends on its mass. The heavier the body, the faster it falls. Observing that each of us can do in everyday life, it would seem to confirm this. Try both out of hand light toothpick and a heavy stone. Stone quickly hits the ground. Such observations have led Aristotle to the conclusion that the fundamental property of the force with which the earth attracts other bodies. In fact, the rate of incidence is affected not only the force of gravity, but the force of air resistance. The ratio of these forces for light and heavy objects differently, which leads to the observed effect.
The Italian Galileo questioned the conclusions of Aristotle and found a way to test them. To do this, he would throw a Leaning Tower of Pisa in the same time shot and much lighter musket bullet. Both bodies have approximately the same streamlined shape, so for the kernel, and a bullet air resistance forces were negligible compared with the forces of attraction. Galileo found that both subjects reaching the ground at the same time, that is, their rate of incidence is the same.
The results of Galileo – a consequence of the law of universal gravitation and the law under which the acceleration experienced by the body is directly proportional to the force acting on it and inversely proportional to the mass.
3. Another experiment of Galileo Galilei
Galileo measured the distance that balls rolling down an inclined board, crossed over at regular intervals, measured by the author learned to water-clock. Scientists have found that if the time to double, the balls ride in four times more. This quadratic dependence means that the balls under gravity are accelerated, contrary taken on faith for 2000 years Aristotle’s assertion that the body on which a force moves with constant speed, whereas if the force is applied to the body, it is at rest. The results of this experiment, Galileo, as the results of his experiment with the Leaning Tower, later served as the basis for the formulation of the laws of classical mechanics.
4. Henry Cavendish Experiment
After Isaac Newton formulated the law of gravity: the force of attraction between two bodies with masses of Meath, distant from each other by a distance r, is F = γ (mM/r2), remained to determine the value of the gravitational constant γ – To do this it was necessary to measure the strength of attraction between two bodies of known masses. Make it not so easy because the force of gravity is very small. We feel the force of Earth’s gravity. But to feel the attraction of even very large was nearby mountains is impossible, because it is very weak.
We needed a very delicate and sensitive method. He invented and used in 1798 by compatriot Newton, Henry Cavendish. He used a torsion balance – balance beam with two balls, hanging on a very thin cord. Cavendish measured the displacement of the beam (rotation) when approaching the scale of other balls balls greater mass. To increase the sensitivity of the displacement was determined by a light spot reflected from the mirrors, mounted on balloon rocker. As a result of this experiment, Cavendish could fairly accurately determine the value of the gravitational constant and the first time to calculate the mass of the Earth.
5. Experiment by Jean Bernard Foucault
French physicist Jean Bernard Leon Foucault in 1851 experimentally proved the Earth’s rotation around its axis by 67-meter pendulum, suspended from the top of the dome of the Pantheon in Paris. The plane of the swing of the pendulum keeps constant position relative to the stars. The observer is located on the Earth and rotating with it, seeing that the plane of rotation slowly rotates in the opposite direction of rotation of the Earth.
6. Experiments of Isaac Newton
In 1672, Isaac Newton did a simple experiment, which is described in all textbooks. Shutters, he has done them a small hole through which passed a sunbeam. On the path of the beam was placed a prism and a prism – the screen. On the Newton observed the “rainbow”: a white ray of sunlight passing through a prism, into a few colored rays – from violet to red. This phenomenon is called dispersion of light.
Sir Isaac was not the first who observed this phenomenon. At the beginning of our era it was known that large single crystals of natural origin have a property to decompose the light into colors. The first investigations of the dispersion of light in the experiments with glass triangular prism before Newton performed Englishman Hariot and the Czech scientist Marci.
However, Newton’s such observations were not subjected to serious analysis, and is on the basis of their findings are not double-checked by additional experiments. And Hariot, and Marci were followers of Aristotle, who argued that the difference in color is determined by the difference in the amount of darkness, “tainted” the white light. Violet, according to Aristotle, occurs when the greatest add darkness to light, and red – at the least. Newton also has done additional experiments with crossed prisms, when the light passed through a prism, then passes through another. Based on the totality of the experiments done, he concluded that “no color does not arise from white and black, mixed together, except the intermediate dark, the amount of light does not change the type of color.” He showed that white light should be considered as an integral. Basically, they are the colors from violet to red.
This experiment Newton an excellent example of how different people are observing the same phenomenon, interpret it differently, and only those who questioned his interpretation and puts additional experiments, come to correct conclusions.
7. The experiment of Thomas Young
Prior to the beginning of the XIX century dominated by notions of the corpuscular nature of light. Light was considered to consist of discrete particles – corpuscles. Although the phenomenon of diffraction and interference of light observed by Newton (“Newton’s rings”), the conventional wisdom has remained corpuscular.
Considering the wave on the surface of the water from two abandoned stone can be seen as superimposed on each other, the waves can interfere, that is vzaimogasit or mutually reinforce each other. Based on this, the English physicist and physician Thomas Young did in 1801, experiments with a beam of light that passed through two holes in an opaque screen, thus forming two independent light source, similar to two thrown stones into the water. As a result, he observed an interference pattern consisting of alternating dark and white bands, which could not be formed, if light consisted of corpuscles. The dark bands correspond zones, where light waves from two slits dampen each other. Bright bands appeared where light waves are mutually reinforcing. Thus was proved the wave nature of light.
8. Experiment Klaus Jonsson
German physicist Klaus Jonsson held in 1961, an experiment similar to the experiment of Thomas Young of light interference. The difference was that instead of light rays Jonsson used electron beams. He received an interference pattern, similar to that Jung observed for light waves. This confirmed the correctness of quantum mechanics on the hybrid wave-particle nature of elementary particles.
9. Robert Millikan experiment
The notion that the electric charge of a body is discrete (ie, consists of larger or smaller set of elementary charges, which are no longer subject to crushing), emerged in the early XIX century and was supported by such famous physicists like Michael Faraday and Helmholtz. In theory coined the term “electron”, signifying a kind of particle – the carrier of the elementary electric charge. This term, however, at that time was purely formal, since neither the particle nor the associated elementary electric charge have not been detected experimentally. In 1895 K. X-rays during the experiments with the discharge pipe discovered that its anode under the action of flying from the cathode rays can emit their own, X-rays or X-rays. In the same year the French physicist Jean Perrin showed experimentally that the cathode rays – a stream of negatively charged particles. But despite the enormous experimental material, the electron remains hypothetical particle, since there was no experience in which would be attended by individual electrons.
The American physicist Robert Millikan developed a method that has become a classic example of fine physical experiment. Millikan succeeded in isolating a charged space of a few drops of water between the plates of the capacitor. Illuminating the X-rays, could be slightly ionize the air between the plate and change the charge drops. When the field between the plates drops slowly moved upward by the electric attraction. When off the field, she fell under the influence of gravity. Off and on the field, it was possible to examine each of the suspended droplets between the plates within 45 seconds, after which they evaporated. By 1909, managed to determine that the charge of any droplets always been an integral multiple of the fundamental value of e (elementary charge). This was convincing proof that electrons are particles with identical charge and mass. Replacing water droplets of oil, Milliken was able to extend observations to 4,5 hours and in 1913, excluding one after the other possible sources of error, published the first measurement value of the electron charge: E = (4,774 ± 0,009) x 10-10 electrostatic units .
10. Experiment Ernest Rutherford
By the beginning of XX century it became clear that atoms consist of negatively charged electrons, and some of the positive charge, due to which the atom remains broadly neutral. However, assumptions about what it looks like this “positive-negative” system, it was too much, while the experimental data, which would make the choice in favor of a particular model, is clearly lacking. Most physicists have adopted a model Dzh.Dzh.Tomsona: atom as a uniformly charged positive sphere with a diameter of about 108 cm with floating inside negative electrons.
In 1909, Ernest Rutherford (he was helped by Hans Geiger and Ernest Mars den), an experiment to understand the actual structure of the atom. In this experiment, a heavy positively charged particles moving at a speed of 20 km / s, passed through a thin gold foil and scattered by the atoms of gold, deviating from the original direction of motion. To determine the degree of deviation, Geiger and Mars den had a microscope to observe the flash on the plate scintillate arose where the plate and hit a particle. During the two years it was regarded a million flashes and proved that approximately one particle per 8000 as a result of scattering changes the direction of more than 90 ° (ie, turns back). This could not possibly happen in the “loose” Thomson atom. The results clearly showed the benefit of the so-called planetary model of the atom – a tiny solid nucleus measuring approximately 10-13 cm, and the electrons orbiting the nucleus at a distance of about 8.10 cm
Modern physics experiments much more difficult experiments of the past. Some devices are placed on the squares in the tens of thousands of square kilometers; while in others fill the volume of the order of a cubic kilometer. A third general will soon be conducted on other planets.