The earth weighs 60 trillion tons, why can it float in space and not fall down?
From birth to death, all of us live on the earth, so the phenomena we see, the laws we master, our common sense and intuition all come from the surface of the earth.
Then what do we feel most often on earth? What do we see?
The most intuitive feeling is that standing on the ground is divided into up and down, and there is a sense of direction, the ground on the foot is down, and the sky above the head is up; we will see objects that are denser than air fall to the ground all day long.
So we summed up such a rule from it: heavy objects are bound to fall from a high place to a low place.
Why is this? Because of the existence of universal gravitation, there will be gravitational action between two mass objects, and the earth will attract all the objects within its gravitational range;
So on the earth we can stand firmly on the ground, our body organs tell us the sense of direction, and mass objects will fall to the ground under the action of gravity.
Then the mass of the earth has reached 60 trillion tons, why is such a giant floating in the space of the universe, why does it not keep falling down?
Actually, this question is not a problem, it is just a misunderstanding of our intuition.
First of all, in the vacuum of the universe, there is no so-called direction at all. Any spatial position is physically equivalent. There is no so-called up and down, left and right, front and rear. The direction is only artificially prescribed, so the earth "goes down"Drop”, this question does not hold.
The second thing we need to know is, why does the object move?
I believe you still remember Newton’s first law, which is the law of inertia. It says: when an object is not subjected to external force, it will always remain stationary or move in a straight line at a constant speed, only when the net force received is not zero, The state of the object will change.
The object on the earth falls to the ground because the object receives the gravitational force given to it by the earth, and the motion state of the earth in the universe is directly related to the force it receives.
If the earth is in the deep cosmic space and there is no celestial body around to exert gravity on the earth, then we will know that the force on the earth is zero.
Then the earth itself will be at rest in the universe, or move in a straight line at a uniform speed. As to which direction the earth will move in a straight line at a uniform speed, it does not matter, after all, there is no such thing as a direction in the universe.
But we know that the earth is not in an empty space. The earth is part of the solar system, surrounded by the sun and 7 planets besides the earth, as well as some dwarf planets and small celestial bodies.
These celestial bodies all exert gravitational force on the earth, but the mass of the sun itself accounts for 99.8% of the matter of the entire solar system, so the motion of the earth is mainly affected by the gravity of the central sun.
So the state of motion of the earth in the universe is not stationary or linear motion at a uniform speed. It is subjected to a gravitational force toward the center of the sun.
Theoretically speaking, the earth should be pulled towards the sun by the sun's gravitational force and fall on the surface of the sun, as if an object fell on the surface of the earth by the gravitational force of the earth, but the real situation is:
Under the action of gravity, the earth moves in an elliptical orbit around the sun. Why is this happening?
Because the earth is under the gravitational force of the sun, it also has a tangential velocity perpendicular to the direction of gravity. This velocity ensures that when the earth falls towards the center of the sun, it will always miss the sun and will not collide with the sun.
So we can think that the earth is actually falling in space, but the direction of falling is not the direction of the south pole or the north pole as we think, but the direction of the center of the sun.
In order to understand this problem, I will give a simple example. This example is also a thought experiment that Newton did in the past. This thought experiment is called the Newton Cannon. It is the theoretical basis for humans to launch satellites around the earth.
We launch a cannonball vertically upwards, which is the green ball in the picture above, then the ball will receive a gravitational force towards the center of the earth. This gravitational force will cause the velocity of the ball to decay until it is zero, and thenIt begins to accelerate to the earth under the action of gravity.
Therefore, launching shells or rockets vertically cannot escape the gravity of the earth at least it cannot be done with the current capabilities of human beings, nor can the shells rotate around the earth in orbit.
So if you want the cannonball to revolve around the earth or leave the earth, you need to provide a horizontal initial velocity for the cannonball and launch the cannonball ahead of time. It looks like the picture below.
Suppose a cannon is mounted on a high mountain and the cannonball is fired ahead. When the cannonball is flying forward, it will fall on the ground under the action of gravity. If the initial velocity of the cannonball is not enough, the cannonball will fly a distance and hit the ground.As shown in a and b in the above figure.
If you increase the initial velocity of the cannonball, when the velocity reaches the first cosmic velocity of 7.9 km/s, then the trajectory of the cannonball will become C;
This is because the earth is a ball, and it has a certain curvature. As long as the shell has enough initial velocity, when it falls on the earth, this speed will make the shell constantly miss the surface of the earth and eventually rotate around the earth.
If the speed is higher, the trajectory of the cannonball will become D. If the speed is higher and reach the second cosmic speed of 11.2km/s, then its trajectory will become E, directly escaping from the earth’s gravity control.
The whole process is the same as in the picture above. This is the principle of human launching satellites around the earth. The rocket first pushes the satellite vertically to a sufficient height, and then the rocket will have an angle with the vertical direction to provide sufficient level for the satelliteSpeed so that the satellite can orbit the earth.
It is not that we think that the rocket sends the satellite into space vertically. If this is the case, the satellite will fall to the ground due to gravity.
The process of artillery shells satellites orbiting the earth is the same as the earth and the sun. The earth is falling towards the sun, but the orbital speed of the earth ensures that the earth will always miss the sun's surface, so the earth will not collide with the sun.
If the speed of the earth orbiting the sun is reduced, the orbit of the earth will attenuate and it will be closer to the sun. When the speed of the earth is low enough, the earth will fall towards the sun at perihelion and collide with the sun.
If the orbital speed of the earth is increased, it will miss more and more from the sun, that is, the orbit becomes larger and larger, and it will gradually move away from the sun.
This is the principle that humans take the earth away from the solar system in "The Wandering Earth". Accelerate the earth and it will leave the solar system.
So to summarize, the earth does fall in the universe, but the direction is the center of the sun, why not crash into the sun, because the earth has a high speed, which ensures that the earth can miss the surface of the sun.
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