Problem description:
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Analysis:
Ten "Most Beautiful" Physics Experiments
The simplest instruments and equipment have discovered the most fundamental and simple scientific concepts. These experiments "caught" the "most beautiful" scientific soul in the eyes of physicists. Just like historical sites, people's long-term confusion and ambiguity were swept away in an instant, and their understanding of nature became clearer.
Robert Crais is a faculty member in the Philosophy Department of new york University at Stony Brook and a historian at Brookhaven National Laboratory. He recently conducted a survey among American physicists, asking them to nominate the most beautiful scientific experiment in history. The Physical World published in September published the first 10 most beautiful experiments, most of which are well-known classics. Surprisingly, most of the top ten experiments were done by scientists independently, with at most one or two assistants. All the experiments were carried out on the experimental platform, without using large computing tools such as computers, but only a ruler or calculator at most.
From the selection of the top ten classic scientific experiments, we can also clearly see the most important discovery trajectory of scientists since 2000, just like we have a bird's eye view of history.
"Physical World" ranks these experiments according to the public's understanding of them. The first experiment is to show the quantum characteristics of the physical world. However, the development of science is a process of accumulation. On September 25th, American magazine * * * rearranged these experiments in chronological order and made a simple explanation.
Eratosthenes measures the circumference of the earth.
A small town in ancient Egypt is now called Aswan. In this small town, the sun hangs high overhead at noon in summer: objects have no shadow, and the sun shines directly into deep wells. Eratosthenes was the curator of the Alexandria Library in the 3rd century BC. He realized that this information could help him estimate the circumference of the earth. On the same day and at the same time in the following years, he measured the shadow of an object in the same place in Alexandria. It is found that the sun's rays are slightly inclined, deviating from the vertical by about 7 degrees.
The rest is the problem of geometry. Suppose the earth is spherical, its circumference should be 360 degrees. If the two cities form an angle of 7 degrees, it is 7/360 of the circumference, which is the distance of 5000 Greek stadiums at that time. So the circumference of the earth should be 250,000 Greek stadiums. Today, through orbit measurement, we know that the measurement error of Eratosthenes is only within 5%. (ranked seventh)
Galileo's experiment of free fall
At the end of 16, everyone thinks that heavy objects fall faster than light objects, because the great Aristotle once said so. Galileo, who worked in the department of mathematics at the University of Pisa at that time, boldly challenged the public's views. The famous experiment of the leaning tower of Pisa has become a scientific story: he dropped a light and a heavy object from the leaning tower at the same time, so that everyone could see that both objects landed at the same time. Galileo may have lost his job at the cost of challenging Aristotle, but he showed the essence of nature, not the authority of human beings, and science made the final decision. (ranked second)
Galileo's accelerated experiment
Galileo continued to improve his views on the motion of objects. He made a smooth straight wooden trough more than 6 meters long and 3 meters wide. Then fix the wooden trough obliquely, let the copper balls slide down the inclined plane from the top of the wooden trough, measure the time of each sliding of the copper balls with a water clock, and study the relationship between them. Aristotle predicted that the speed of rolling ball was uniform; The copper ball rolls twice as long and walks twice as far. Galileo proved that the rolling distance of the copper ball is proportional to the square of time: in twice the time, the copper ball rolled four times because of the constant acceleration of gravity. (ranked eighth)
Newton prism decomposes sunlight.
Galileo died the year he was born in isaac newton. Newton graduated from Trinity College of Cambridge University in 1665, then stayed at home for two years to avoid the plague, and then successfully found a job. At that time, everyone thought that white light was pure light without other colors (Aristotle thought so), and colored light was a kind of light that changed somehow.
To test this hypothesis, Newton put a prism in the sun, and through it, it was decomposed into different colors on the wall, which we later called spectrum. People know that rainbows are colorful, but they think it is because they are abnormal. Newton's conclusion is that it is red, orange, yellow, green, cyan, blue and purple that have different chromatograms and form a single white light on the surface. If you look deeply, you will find that white light is very beautiful. (ranked fourth)
Cavendish torque experiment
Another great contribution of Newton is his law of universal gravitation, but how big is universal gravitation?
/kloc-at the end of 0/8, the British scientist Henry cavendish decided to find out this gravity. His 6-foot-long wooden stick, with small metal balls tied to both sides, is hung by wire like a dumbbell; Then, two 350-pound shot putters are brought close together to generate enough gravity to rotate the dumbbell and twist the wire. And then use a homemade instrument to measure tiny
Turn around.
The measurement results are surprisingly accurate. He measured the parameters of the gravitational constant, and on this basis, cavendish calculated the density and mass of the earth. Cavendish's calculation shows that the earth weighs 6.0× 1024 kg, or 13 trillion pounds. (Ranked sixth)
Thomas Young's Optical Interference Experiment
Newton was not always right. After many arguments, Newton made the scientific community accept that light is composed of particles, not waves. 1830, Thomas Young, a British doctor and physicist, verified this view with experiments. He punched a small hole in the shutter, then covered it with thick paper and poked a small hole in the paper. Let the light pass through and reflect the transmitted light with a mirror. Then he used a piece of paper about 1/30 inches thick to divide the light into two beams in the middle. As a result, I saw the cross light and shadow. This shows that two beams of light can interfere with each other like waves. This experiment played a vital role in the establishment of quantum theory a century later. (ranked fifth)
Michel foucault pendulum experiment
Last year, scientists placed a pendulum clock in the South Pole and observed its swing. They are a famous experiment in Paris in 185 1 year. 185 1 year, French scientist michel foucault made an experiment in front of the public. Hang a 62-pound iron ball under the roof with a 220-foot-long steel wire with an iron pen, and observe and record its trajectory of swinging back and forth. week
It is not surprising that the audience finds that the pendulum will slightly deviate from the original track and rotate every time it swings. In fact, this is because the house moves slowly.
Foucault's argument shows that the earth rotates around its axis. At the latitude of Paris, the trajectory of the pendulum is clockwise with a period of 30 hours. In the southern hemisphere, the pendulum should turn counterclockwise, but it won't turn at the equator. At the South Pole, the rotation period is 24 hours. (Ranked 10th)
Robert milliken Oil Drop Experiment
Scientists have been studying electricity for a long time. It is known that this invisible substance can be obtained from lightning in the sky or by rubbing hair. 1897, the British physicist J. J. Thomas has determined that the current is composed of negatively charged particles, that is, electrons. 1909 American scientist Robert milliken began to measure the charge of electric current. Milliken used a perfume bottle nozzle to spray droplets into a small transparent box. The top and bottom of the small box are connected with batteries, so that one side becomes a positive plate and the other side becomes a negative plate. Oil droplets will absorb some static electricity when passing through the air, and the falling speed of oil droplets can be controlled by changing the voltage between the plates.
Milliken constantly changed the voltage and carefully observed the movement of each drop of oil. After repeated experiments, milliken came to the conclusion that the value of charge is a fixed constant, and the smallest unit is the charge of a single electron. (ranked third)
Rutherford discovered the nuclear experiment.
19 1 1 year, when Rutherford was still doing radioactive energy experiments at Manchester University, atoms were remembered as "raisin pudding" with a large number of paste-like substances and electronic particles with positive charges in the middle. But he and his assistant were very surprised to find that a small amount of positively charged alpha particles were bounced back when they were fired at the gold foil. Rutherford calculated that atoms are not mushy substances, and most of them are concentrated in a central nucleus, now called nucleon.
Electrons surround it. (ranked ninth)
Thomas Young's double-slit demonstration is applied to the experiment of electronic interference, but Newton and Thomas Young's conclusions about the study of the properties of light are not completely correct. Light is neither a simple particle nor a simple wave. At the beginning of the 20th century, Max Pockrone and Albert Einstein respectively pointed out that something called photon can emit light and absorb light. But other experiments have proved that light is a wave. After decades of development, quantum theory has finally summed up two contradictory truths: photons and subatomic particles (such as electrons and photons). ) is a particle with two properties at the same time, which is physically called wave-particle duality.
The transformation of Thomas Young's double-slit demonstration can well illustrate this point. Scientists use electron flow instead of light beam to explain the experiment. According to quantum mechanics, the charged particle flow is divided into two streams, and the smaller particle flow produces wave effect, which interacts with each other to produce enhanced light and shadow similar to that in Thomas Young's double-slit demonstration. This shows that particles also have fluctuation effect.
Peter Rogers, editor of Physical World, speculated that it was not until 196 1 that a scientist did this experiment in the real world. (ranked first)