This story sounds really famous and beautiful, but you think gravity is the truth behind everything. Although it is the essential attribute of things, this truth is deeply hidden. Can an apple sober Newton up? And if you think about it carefully, can you believe that Newton never saw anything fall except apples in his life? Obviously impossible, Newton can see objects falling to the center of the earth at any time! Then why did an apple create Newton's myth? Not a cup or a pen? Obviously, this myth is just a myth, and it is ok for children to see it. To truly understand science, we must know how Newton himself discovered gravity.
First of all, how did Newton's apple myth come about? In fact, this incident is not an anecdote. Newton told others in his later years, and so did his related descendants, including Newton's biography written by Newton's fellow villagers. So what is certain is that Newton himself said the incident of apple hitting the head. So the question is, why did Newton invent an apple myth? We'll talk about this later. As we know, any scientific theory is not produced out of thin air, and it must have the efforts and contributions of predecessors. So is gravity.
Before Newton, many great physicists and astronomers had laid the foundation for the birth of Newton's theory. Newton himself said this sentence, and everyone is familiar with it: If I see farther than others, it is because I stand on the shoulders of giants. So who is this giant Newton is talking about? I think there are three: Kepler, Galileo and Descartes. The contributions of these three people basically indicate that new physics is about to be born, and what is lacking is Newton's genius. You see, Heliocentrism ruled mankind for nearly 2000 years until 1543, when Copernicus published the Theory of Celestial Motion, which reversed the positions of the earth and the sun.
Heliocentrism was born. At that time, Heliocentrism of Copernicus still continued the orbit of uniform circular motion in geocentric theory, that is, the orbit of the planet was still a perfect circle, rotating around the sun at a uniform speed. Although this model is closer to the fact, it is not more accurate than Ptolemy's current model to predict the celestial movement at that time. So this model is not perfect, obviously there is a big problem. Then Kepler appeared, and he passed Tycho? A large number of observation data obtained by Bula define the orbit of the planet as an ellipse by fitting and guessing, and the sun is at one of the focuses of the ellipse. This is Kepler's first law of planetary motion and the second and third laws, so I won't go into details here.
Kepler's law is put forward, and it is applied to the planets of the sun and comets to calculate the celestial orbits, which are in good agreement with the known data at that time. This shows that Kepler's heliocentric model truly and accurately describes the real situation of planets of the solar system's motion. But Kepler's law can only be said to be above the appearance of things and belongs to empirical theory. He can't explain why the planets revolve around the sun after the celestial sphere is broken, and why the orbits of the planets are elliptical. And other problems, because these problems are related to the essential reason of things, that is, the real scientific theory behind it, not the rule of thumb.
So after Kepler's three laws were put forward, not many people believed them at first. After all, you didn't fully answer their questions. However, with Galileo's discovery of Jupiter's satellite in 1609 and the discovery of Venus' phase transition, people began to gradually accept Heliocentrism. 163 1 year, people used Kepler's law to predict the transit of Venus and Mercury, which had never been observed before. At this point, people finally accepted Kepler's solar system model, but in this case, there is a problem that needs the whole scientific community to find an answer. That is, the new model of the universe needs new physics as a support to solve the intractable diseases left by Kepler.
Let's talk about Galileo here. His contribution to mechanics is still considerable. The famous experiment of leaning tower of Pisa (the inclined plane experiment must have been done) overthrew Aristotle's statement that an object is forced to move, and force is to maintain the movement of the object. Galileo believed that force was only the reason for changing the speed of an object. This is very important for Newton because it is very close to Newton's second law. The following is Descartes,/kloc-the genius of the 7th century. He is a pioneer of modern physics revolution and a solid founder of Newtonian mechanics.
He proposed that the universe is made up of matter and motion, that's all. This thought broke the distinction between heaven and earth that Aristotle thought. In other words, we can explain that the theory of things on earth can also be applied to heaven. There is no heaven or earth at all. Heaven and earth are the same and follow the same physical laws. This is also very important, because this idea made Newton dare to treat apples and the moon equally, and dare to extend the falling force of apples to the moon and other celestial bodies.
In addition to the above ideas, Descartes also proposed that the motion of objects in the universe can be maintained by itself and the quantity is conserved. Does this look familiar to you? Yes, this is the law of inertia and Newton's first law. Therefore, Newton's success lies not only in his genius-like views, but also in the full preparations made by his predecessors. Now let's talk about Newton. He is a genius that has never been seen before, and it is rare to see him for hundreds of years. No matter where you go, you are so outstanding, outstanding and dazzling. Newton 166 1 When studying in Trinity College, Cambridge, they basically taught themselves. What the school taught didn't fall into his eyes at all. He absorbed the latest and cutting-edge theories of astronomy, philosophy and mathematics at that time. Of course, Newton must have known the contributions of the predecessors I mentioned above, and he had his own superior views. He also knows what problems the new science needs to solve. Get the motion law of the object.
And all the top scientists at that time knew that the free fall of objects on the earth was due to a force, which changed the state of objects. What is this force? How to describe it with mathematics is the most critical problem. Obviously, this force is a kind of action at a distance, and objects can influence each other without contact. At that time, except Newton who dared to take it seriously, no one else really had the courage. We know that apart from science, Newton's greatest hobby was to burn stoves, make pots and engage in his own alchemy. He believes in that magical thing. Some people say that Newton was the last magician in human history. So this kind of Newton's psychology is not exclusive when facing the function of distance. He believes that the universe is controlled by a free-will God, which is nothing at all. Even Aristotle couldn't believe this long-distance action.
So Newton did a lot of calculations when he avoided the plague at home in 1665. He wanted to see if this superpower could explain the movement of the moon, so he extended the force that caused the apple to fall on the moon. First, he deduced the formula of centrifugal force, measured the acceleration of gravity of the earth (through a simple pendulum), and then multiplied the acceleration of the surface by the mass of the moon to calculate the gravity of the moon on the earth's surface. Then the centrifugal force of the moon is calculated according to the centrifugal force formula, and the final conclusion is that the gravitational force of the moon on the surface is equal to 4325 times of the centrifugal force of the moon. Then he deduced the inverse square formula according to Kepler's third law. In other words, the magnitude of this supergravity is inversely proportional to the square of the distance between objects.
Because the distance between the earth and the moon is 60 times the diameter of the earth, it is concluded that the attraction of the moon on the surface of the earth should be equal to 3600 times the centrifugal force of the moon. The data used by Newton at that time, including the mass, distance and period of revolution of the moon, were not very accurate. He is a little confused about this calculation. These two values are not equal. At that time, he thought to himself, maybe this distance force cannot explain the motion of celestial bodies. Then I put the question on hold. So Newton didn't understand gravity at all during the plague. Not even a piece. So there is no apple myth. Newton thought about this problem in the next few years, but he still liked alchemy. In science, Newton also prefers to do optical experiments than gravity, so it can be said that his focus is not on gravity.
Let Newton pick up the gravity problem again in Hooke's letter to Newton in 1679, which shows that he is also studying this problem. We know that Newton and Hooke had an issue because of optical problems. These two men can be said to have fought with each other, and no one can take anyone seriously. So Hooke's letter stimulated Newton, who reconsidered and calculated the problem of gravity in the next few years. Of course, this calculation result is very close to the fact, but there may still be some problems. And the person who directly led to the birth of Newton's gravity was Edmund? Harry. Harley was ten years younger than Newton, but by this time Harley was already a professor of astronomy at Oxford University. His main research goal is comets. He wants to prove that several comet records observed by people in history are actually a return of comets. However, it is difficult to face such a strange comet orbit. In fact, Harley, Hooke and others have known that the force on the planet is inversely proportional to the square of the distance. In other words, they also deduced this result through Kepler's third law.
However, their mathematical ability is not good, so they can't carry out strict mathematical deduction and deduction process, so they can't prove that the inverse square force will inevitably lead the planet to orbit the sun in an elliptical orbit. So Harley had to go to Cambridge to visit Newton. Newton's mathematical ability is notoriously good. Harley asked Newton: If the force on the planet is inversely proportional to the square of its distance, what kind of curve is the orbit of the planet? Newton blurted out at that time, it must be an ellipse, and I worked it out. Newton said at the time that his calculation result was lost (he thought there was something wrong with the calculation), but promised Harley that he could recalculate it immediately and send it to Harley. In this way, under the impetus of Harley, Newton felt that his idea was not wrong, and so was the distance force that he initially believed through alchemy intuition.
In the next three months, Newton lost his favorite alchemy and the stove stopped burning. In these three months, Newton seems to have died. Through rigorous mathematical deduction, he strictly proved that any celestial body moving in an elliptical orbit will be subjected to a force inversely proportional to the square of the distance. Of course, an object subjected to an inverse square force must make an elliptical motion. After seeing it, Harley marveled at Newton's god-like mathematical ability. Moreover, Newton used his own calculus to prove that R of the formula of universal gravitation is the distance between the centers of two celestial bodies. With Harley's support, Newton published his achievement in 1687, which is the representative work of natural philosophy, Principles of Mathematics. This is the first complete set of natural science theory and the first complete set of mechanical system in human history.
Newton is also the first time in human history to deduce all the empirical laws known at that time with more basic and profound scientific laws. Combining universal gravitation with tripod's law, Kepler's three laws can be deduced completely. It also explains the problems left by Kepler's three laws and lets people know the more essential reasons behind planetary motion. Of course, Harley also used Newton's theory to accurately calculate the orbital parameters and periods of comets. As Harley guessed, the comets recorded in 1682, 1607 and 153 1 year are indeed the same. Moreover, Newton's theory is used to predict that this comet will return on1758 65438+February 25th. This is the famous halley's comet. It is expected that the next return will be in 2062. This is the birth of Newton's gravity, not only because of the efforts and confidence of his predecessors, but also because of his intuition about alchemy. Besides, it took Newton 20 years to find out the theory of gravity from an apple? Can you believe it?
Then why did Newton invent this myth in his later years? As mentioned earlier, in the process of Newton's discovery of gravity, other scientists are also studying it. After all, he is not the only one who introduced inverse square force. Moreover, Newton himself and others, especially Hooke, have been pinching each other all their lives, so in his later years, he directly said that he discovered gravity after being hit by an apple during the plague, which can solve the arguments of later generations once and for all. Secondly, Newton himself is arrogant, proud and likes to beautify himself, so making up such a myth is also in line with his style. Finally, such a myth can cover up the fact that he was inspired by alchemy in the process of studying and calculating gravity. An apple can solve all the above problems.