Newton's gravity story

In the countryside, Newton was always troubled by such a question: what drives the moon to go around the earth and the earth to go around the sun? Why won't the moon fall to the earth? Why doesn't the earth fall to the sun?

In the following years, Newton claimed that this happened. Sitting in my sister's orchard, an apple fell to the grass with a bang. He turned quickly to watch the second apple fall to the ground. The second apple fell from the outstretched branch, bounced on the ground and lay quietly on the grass.

This apple is definitely not the first apple Newton saw fall to the ground. Of course, the second apple is no different from the first one. Although the apple landing did not provide Newton with an answer, it inspired the young scientist to think about a new problem: the apple will land, but the moon will not. What's the difference between an apple and the moon?

The next morning, it was sunny, and Newton saw his little nephew playing with a ball. He has a rubber band tied to his hand, and a ball tied to the other end of the rubber band. He swung the ball slowly first, then faster and faster, and finally the ball was thrown straight out.

Newton suddenly realized that the movements of the moon and the ball were very similar. There are two forces acting on the ball, one is the outward driving force, and the other is the tension of the rubber band. Similarly, there are two forces acting on the moon, namely, the driving force of the moon's movement and the pulling force of gravity. It is under the action of gravity that the apple will fall to the ground.

Newton believed for the first time that gravity is not only a force between planets and stars, but also a universal force. He believed in alchemy and thought that matter attracted each other, which led him to assert that mutual attraction applied not only to huge celestial bodies, but also to objects of various sizes. Apples fall, raindrops fall, and planets revolve around the sun, all of which are the results of gravity.

It is generally believed that the laws of nature applicable to the earth are completely different from those applicable to space. Newton's law of universal gravitation gave this view a heavy blow, telling people that the laws governing nature and the universe are very simple.

2. The law of universal gravitation was introduced into China.

Newton's most important work, Mathematical Principles of Natural Philosophy, was published in 1687. The book summarizes many important discoveries and research achievements in his life, including the above-mentioned laws about the movement of objects. He said that this book "mainly studies the resistance of heavy and light fluids and other forces that attract motion, so we study the mathematical principles of natural philosophy."

After the book was introduced into China, Li, a mathematician from China, partially translated it, but it was not published and the translation was lost. The existing Chinese version was translated by mathematician Zheng Taipu, entitled Mathematical Principles of Natural Philosophy, which was reprinted twice by the Commercial Press 193 1 first edition, 1957 and 1958.

3. The simple meaning of gravity:

Newton didn't find gravity. He found that gravity is "everything". Every object attracts other objects, and the magnitude of this attraction is only related to the mass of the objects and the distance between them.

Newton's law of universal gravitation shows that every object will attract every other object, and the gravitation between two objects is directly proportional to their mass, and the mass will decrease with the square of the center distance between two objects. Newton developed calculus in order to prove that only a sphere can concentrate the total mass of the ball on the center of mass of the ball to represent the total effect of gravity of the whole ball.

However, no matter how far away from the earth, the gravity of the earth will never become zero. Even if you are taken to the edge of the universe, the gravity of the earth will still act on you. Although the influence of the earth's gravity may be masked by the massive objects near you, it still exists.

No matter how small or far away, every object will be affected by gravity and spread all over the space, just like what we call "everything"

Extended data:

Newton's law of universal gravitation well explains the gravitation of objects on the ground, the tides of the ocean and the motions of planets and celestial bodies, and it is of great significance to unify the motions in the sky with those on the ground. General relativity is actually a theory about the nature of universal gravitation.

People believe that a massive object will bend the space-time around it. In this curved space-time, all objects will naturally move along the geodesic (also called geodesic), but the distance between them will be closer. We can't see the curvature of space-time, we only see objects approaching each other, so we think there is a kind of "gravity" between them.

In fact, the gravity between objects is not a real force, but a manifestation of the bending of time and space. The curvature of four-dimensional space-time is hard to imagine, but it can be reduced by one dimension (on a two-dimensional plane) as an analogy. Imagine a piece of cloth hanging flat, with a small ball on it, it will bend the cloth, and put a small ball in another place, it will also bend the surrounding cloth.

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