The earth is the whole of mankind and the "mother" of mankind!
Since its birth, the earth has been spinning, constantly rotating to this day, for 4.6 billion years.
Many people will have this question: Why does the earth keep rotating? Why hasn't the 4.6 billion years stopped?
Simply put, because it's not long enough!
What the? 4.6 billion years is not long enough?
Indeed! In the eyes of mankind, 4.6 billion years is too long, but 4.6 billion years is not a long time to rise to the level of the vast universe.
In our daily lives, we often see things that rotate, such as gyroscopes.
But after a few minutes of spinning, the gyroscope usually stops because there is friction during the rotation and the resistance of the wind.
Is there any resistance during the rotation of the earth?
Of course, space in the universe is not an absolute vacuum. But the resistance from space during the rotation of the earth is minimal, especially in the face of the huge mass of the earth, the resistance is even smaller!
So even though the Earth has been rotating for 4.6 billion years, the speed hasn't diminished much.
According to calculations, every hundred years, the time for the Earth to rotate once is about 1.7 milliseconds slower (1 second equals 1000 milliseconds).
That is to say, the time of day on earth is gradually getting longer, but the rate of growth is extremely slow, and we can't feel it at all.
According to the rate at which the Earth is slowing down, it will slow down by 1 second in 60,000 years and 4 hours in 1 billion years. Dinosaurs appeared on Earth 240 million years ago and the time earth lasted 23 hours a day.
So, the biggest question is: Why does the Earth's rotation slow down?
The main reason is not the resistance of space, but because of the moon!
Simply put, four words: tidal gravity!
The tidal gravity from the Moon slows down the Earth's rotation.
100 million years after the Formation of the Earth, the ocean appeared on the surface in large areas, and then the tidal gravitational pull of the Moon began.
The gravitational pull of the Moon makes the Earth perform periodic tidal action, constantly consuming the Rotation Energy of the Earth, making the Earth rotate more and more slowly.
At the same time, tidal action also allows the moon to move away from the Earth at a rate of about 3.8 centimeters per year.
Why?
Take a popular example.
In reality, many people have ridden a running wooden horse. Suppose your goddess is riding a merry-go-round at the moment, and you are riding a real-life horse chasing your goddess around the perimeter of the carousel.
Since the carousel is too fast and the real horse is running slower (just assuming here, not more real), you want to catch up with your goddess as soon as possible and go hand in hand with her.
You are lucky that your goddess happens to have a rope in her hand, and she loves you so much that she threw the rope directly at the real horse, just so that it happened to wrap around the horse's neck.
So the carousel rides the real horse, the real horse is getting faster and faster, and finally the speed reaches the same as the carousel, and you can finally show love side by side!
The whole process is that the energy of the carousel is transmitted to the real horse, and when you stand shoulder to shoulder, the real horse can no longer obtain the energy.
In the example, the real horse you ride is the moon, the carousel is the earth, and the rope thrown by the goddess is gravity.
In fact, there is a rope between the earth and the moon that we can't see.
Since the formation of the Earth-Moon system, the Earth has been dragging the Moon all the way, making the Moon's speed gradually faster.
Faster speed means that the moon's orbit is rising, gradually moving away from the Earth, and the Earth's rotation speed is gradually slower.
Once the time of the Earth's day is equal to one month, the tidal acceleration between the Moon and the Earth will suddenly stop!
It is estimated that one day at that time would be equivalent to 47 days now, and this state of the Earth and moon would be called the Cassini state.
Still can't understand?
It's okay, let's go another way. In fact, the Earth and the Moon are like a spinning figure skater.
Figure skaters often use the following movements during the performance: during the spin, first open their arms, and then their arms are close to the body, the purpose is to make the rotation speed faster.
Why does it get faster? Because angular momentum is conserved.
By the same token, the Earth's lunar system begins like a figure skater with his arms clasped close together, and then the moon moves away from the Earth and the Earth begins to spin slower.
It's like a figure skater with arms outstretched.
The Moon's tidal gravitational pull on the Earth causes the Earth's oceans to move, and the Earth's moment of inertia changes accordingly.
Depending on the conservation of angular momentum, the rotation rate of the Earth (solid Earth) changes.
The constant exchange of angular momentum between the ocean and the Earth (solid Earth) changes the Rotation Rate of the Earth.
Is there any evidence that the Earth's rotation is slowing down?
Of course. According to modern geological and archaeological research, the study of fossils of living organisms can tell that the earth's rotation rate is slowing down. For example, the length of the day hundreds of millions of years ago can be calculated from the rings of coral fossils, as shown in the following figure:
So is it only the Moon that affects the Earth's rotation speed?
Of course not, there are other reasons, but the moon's influence dominates. There is also the impact of the Earth's own super tsunami. For example, the Indonesian super tsunami in 2004 accelerated the rotation speed of the earth by about 3 microseconds, but such an impact is completely negligible in the long history of the earth.
Since the Earth's rotation rate will become slower and slower, will the Earth eventually stop rotating?
Here's a point. Usually what we call "the moon revolves around the earth" is actually not rigorous, because as a satellite, the mass of the moon is too large, so the earth and the moon are more like a pair of binary star systems, and the two planets rotate around each other. It's just that the Mass of the Earth is relatively large, and it feels as if the Moon is orbiting the Earth.
Theoretically, the tidal gravitational effect of the moon on the earth will continue until a distant day, when the orbital period of the moon matches the rotation of the earth, and then the moon is completely locked by the earth, hanging motionless somewhere above the earth (expecting the moon to hang over our country).
It's just that we may never wait for this day, because it is so long, so long that even if the sun becomes a red giant, devouring Mercury, Venus, and even the Earth, this day is still far from coming.
Scientists estimate that it will take about two billion years for Earth to lock on to the moon! In addition to the fact that the Earth will lock on to the Moon, our Sun is also slowly locking on the Earth, which will take a much longer time, about five billion years!
Think about what it will look like in 50 billion years...
Forget it, let's move the bricks!