Like the other eight planets in the solar system, the earth revolves around the sun and constantly revolves around an imaginary rotation axis, which is the rotation of the earth.

Hundreds of years ago, people suggested that

There are many ways to prove the rotation of the earth. The famous Foucault pendulum lets us really see the rotation of the earth, but why does the earth rotate around its axis? Why does it revolve around the sun? This is a science that has been developed for many years.

Scientists are very interested in this problem. Roughly speaking, rotation is a basic movement form of celestial bodies in the universe, but to really answer this question, we must first understand how the earth and the solar system formed.

Rotation is closely related to the formation of the solar system.

According to modern astronomical theory, the solar system is formed by the so-called primitive nebula, which is a very thin gas cloud and was disturbed by some kind 5 billion years ago.

Dynamic influence, contracting towards the center under the action of gravity. After a long period of evolution, the density and temperature of the central part of the matter are getting higher and higher, and finally it can trigger thermonuclear reaction and evolve into too.

Yang. The residual gas around the sun gradually forms a rotating disk-shaped gas layer, which gradually gathers into solid particles, micro-planets and primitive planets, and finally forms after shrinking, colliding, capturing and gathering.

Become independent solar system celestial bodies such as planets and asteroids.

We know that to measure the speed of an object moving in a straight line, it can be expressed by speed, so what is the measure of object rotation?

And then what? One way is to use "angular momentum". For an object rotating around a fixed point, its angular momentum is equal to the mass multiplied by the velocity and then multiplied by the distance between the object and the fixed point. There is a very important angular momentum in physics.

The law of constants means that the angular momentum of a rotating object will not change because of the change of its shape if it is not acted by an external torque. For example, a ballet dancer suddenly closes her arms while spinning.

When the distance between the center of mass and the fixed point becomes smaller, his rotation speed will increase, because only in this way can the angular momentum remain unchanged. This law plays an important role in the generation of the earth's rotation speed.

Form the sun

The protonebula of a galaxy has angular momentum. After the formation of the sun and planetary system, its angular momentum will not be lost, but it will inevitably be redistributed. Each star will be separated from the original nebula in the long process of material accumulation.

Get a certain angular momentum. Because of the conservation of angular momentum, the planet will rotate faster and faster during contraction. The earth is no exception, and its angular momentum is mainly distributed in the earth's revolution around the sun and mutual earth-moon system.

This is the origin of the earth's rotation, but scientists need to do a lot of research work to truly analyze the revolution and rotation of the earth and other planets.

That is to say, in the process of the formation of the earth, movement, especially rotation, is accompanied by the formation of the earth from beginning to end, rather than starting to rotate or revolve for some reason after the formation of the earth.