At the beginning of the birth of the universe, the distribution of matter was not uniform. Some places were sparse and some places were dense. The location of the solar system was a relatively dense area.
Of course, the solar system does not exist at this time, there is only a piece of nebula matter. Any object with mass has a mutual gravitational effect, and under the influence of this force, matter begins to gradually gather. The matter gathered from various directions is subject to gravity in multiple directions at the same time, so their movement trajectory is not a simple straight line, but has a slow rotation trend.
During the process of material condensation, the volume of the nebula gradually shrinks, but the rotation speed is getting faster and faster. Why is this happening to
? Because angular momentum is conserved. An object that is rotating has an angular momentum . This angular momentum is related to three factors, namely the mass of the object, the distance between the object and the axis of rotation, and the angular velocity. As matter condenses, the volume of the nebula becomes smaller, so the distance between matter and the axis of rotation is reduced. However, since the angular momentum is conserved, the reduction of distance means that the mass or speed must increase accordingly. Mass is impossible to increase, so the angular speed can only be increased, so this nebula will naturally turn faster and faster.
As the sun finally forms, the distance between matter and the axis of rotation is greatly reduced, and the angular velocity is increased accordingly. In this way, a high-speed rotating star is born.
At the beginning, the rotation speed generated by matter under gravity was very slow, but due to the conservation of angular momentum, it finally achieved a very high speed when the star body was formed. This is the case with the sun, and the other celestial bodies in the solar system, which naturally also include our earth. It is also very easy to experience the conservation of angular momentum in person, just a swing chair and a friend who helps you turn the swing chair.
First, you have to sit in the swivel chair and spread your arms. In order to make the experiment more obvious, you can hold a heavy object in each hand, such as a large beverage bottle filled with water.
At this time, let your friends help you turn the chair. If you retract your arms, you will find that the rotation speed of the swing chair has suddenly increased. On the contrary, if you suddenly stretch your arms out, the rotation speed will immediately drop. This is the conservation of angular momentum. The speed will accelerate when the distance decreases, and the speed will slow down when the distance increases. Similar examples include the actors of ballet . At first, they stretched their arms flat and rotated slowly, but when they stretched their arms toward their heads, the speed suddenly became faster, which is also the conservation of angular momentum.
Since we know how the earth rotates, can we also change the speed of the earth's rotation? It can be done theoretically.
On the surface of the earth, the area farthest from the axis of rotation is the equator, and the area closest to the axis of rotation is the north and south poles. Therefore, we only need to continuously transport the material near the equator to the north and south poles to increase the rotation speed of the earth. On the contrary, if the material from the north and south poles is transferred to the equator, it can slow down the rotation speed of the earth. Of course, this change is not very obvious, because the main weight of the earth is not on the surface, but inside the earth, if we can transfer a large amount of matter inside the earth, it will be able to significantly change the speed of the earth's rotation.
