Lead
The Sun is the center of the solar system, and planets and other distant celestial bodies roam in between, forming a vast system.
However, there is a unique presence in this system: the "earth".
The earth has almost always kept a fixed distance from the sun, not swallowed up by the sun, nor thrown away by the sun, like a drifting bottle flying between the fingers of a child, guarding the sun and not being bound by the sun.
But astronomical objects are affected by gravity, so how does the earth maintain this special state?
How does the Earth "float with the wind"?
1. "Suspended" in space.
One afternoon, Newton was wandering around the orchard in the breeze, whirling along, when he saw an apple fall from a tree.
The apple fell from the tree and fell straight to the ground, and apparently Newton could instantly know why the apple was falling: "The earth is attracting apples."
The earth has a very strong attraction, and this force is "gravity", but the gravity of the earth only plays a role in "making objects centripetal" for some objects, and objects will be attracted to the center of the earth.
To explain why apples always fall downward, Newton came up with a great law, which is the "law of universal gravitation".
Newton's law of universal gravitation states: "The gravitational force between two objects depends primarily on the product of the masses of two objects and the ratio of the square of the distance between them."
To put it simply, the heavier and closer the distance between two objects, the greater the gravitational pull they experience.
The earth is the "big rock".
The mass of the Earth is about 60 trillion tons, and the radius of the Earth is about 6,400 kilometers.
We are on Earth, so the gravitational pull we receive is also in the direction of the center of the earth, and our "down" in the universe often refers to this direction.
According to Newton's formula, the gravitational force between the earth and the object is: G(m1*m2)/r^2, G is the gravitational constant, r is the distance between the object and the center of the earth, and m1 and m2 are the masses of the earth and the object respectively.
It can be seen that the mass and radius of the earth are fixed, and the magnitude of gravitational force mainly depends on the mass of the object and the distance from the center of the earth, so it can be known that the more massive the object, the closer it is to the center of the earth, the greater the gravitational force it is subjected to, which is why we feel that "the closer to the ground, the greater the gravity". ## 2. The Earth does not set towards the Sun.
However, the Earth is not isolated in the universe, it has a partner, and that is the Sun.
The sun is a very hot fireball capable of emitting scorching sunlight outwards and bringing warmth to the earth.
At the same time, the sun is also the largest "heavy stone" in this system.
The mass of the sun is about 300,000 times the mass of the earth, and the range of sunlight is also very wide, with an effective illumination distance of hundreds of millions of kilometers from the light, which is called "halo", and the periphery of the "halo" is the boundary of the "solar system".
The distance between the Earth and the Sun is about 150 million kilometers, and at such a distance, if the Earth were attracted by the Sun's gravity, it would soon be engulfed by the Sun.
According to the formula for calculating the gravitational force between the object and the earth, the gravitational force between the earth and the sun can be obtained.
However, from the calculation results, the gravitational force between the earth and the sun is greater than the gravitational force of the earth, which means that the earth will always be attracted to the sun and thus swallowed by the sun, but obviously the earth is not swallowed by the sun, so Newton's gravitational force not only has such a huge "force to attract others", but also is equivalent to "the force exerted on others", and this force is gravity.
The logarithm of the gravitational difference between the earth and the sun is also very large, but because the distance between the earth and the sun is large, and the centrifugal force on the earth is also very large, the earth revolves around the sun under the combined action of the gravitational force of the sun and the centrifugal force of the earth itself.
The formula for the gravitational force between the Earth and the Sun can be quickly simplified: G(m1*m2)/r^2, since m1 and m2 are the masses of the Sun and the Earth, we can reduce them, and the gravitational force between the Earth and the Sun is the ratio of the square of the distance from the Sun to the product of the mass of the central planet: Gm/r^2.
From the formula, the gravitational pull between the earth and the sun is obviously inferior to the gravitational force between the earth and the earth.
So the gravitational pull between the Earth and the Sun causes the Earth to revolve around the Sun.
But there are not only the sun in the solar system, but also 8 planets, plus these planets have their own moons and stars, so in the solar system, the gravitational pull between the planets is not only from the sun, but also from other planets, and these gravitational forces will also affect the trajectory of the planets.
But the earth is still in space, away from the sun, revolving rhythmically, the sun rises in the east, and then passes through the south and sets in the west, day and night, the four seasons are reincarnated, and the earth works as if it were a giant machine.
However, you can't feel yourself moving on the earth, after all, the diameter of the earth is about 12,742 kilometers, so the "centrifugal force" brought by the earth will be very small, and the "gravitational force" with its own will be very small, so the earth will only slightly produce some friction when it rotates, day after day, reincarnation, and the new year is coming again, which is actually determined by the gravitational force of the sun, and the "four seasons" are also caused by the rotation of the earth.
2. The principle of the motion of an object around a planet.
Since Newton summed up the law of gravitation through the fall of an apple, the phenomenon of the earth's revolution is actually within the scope of the "law" of gravitation.
Newton's law of gravitation: G(m1*m2)/r^2, strictly speaking, this formula only applies to the magnitude of gravitational force between two celestial bodies.
However, when the gravitational pull of other planets is also added, the movement of the Earth becomes complex, and the trajectory and speed of the Earth are also affected by other factors.
However, Newton put forward an important theorem: the "law of motion", which is that in order to keep an object moving in a straight line or not moving at a constant speed, there needs to be a sum of the vector and moment of the external force equal to zero with the object.
And when we introduce the plane motion of an object, we will be talking about a state of motion of an object: the "inertial frame of reference".
In simple terms, in this frame of reference, the object moves in a uniform straight line or does not change its position.
In Newton's "law" of gravitation, m1 is the mass of the earth and m2 is the mass of other stars, because we are observing the motion of other planets above the earth, in an inertial frame of reference, so the force between the earth and other planets is gravitational force.
Under the action of gravitational force, the sun exerts a force on the earth, and the earth also exerts a force on the sun, both of which are equal in size and in opposite directions, so the two celestial bodies are not subject to friction and are always orbiting.
No matter how grand the reason why the earth can always revolve around the sun and move according to a given orbit, how can we not mention the miraculous "force" of gravity.
"Force" is a vector concept, which has a direction and a magnitude, sometimes very weak, sometimes huge.
In the above, the gravitational force between the earth and the sun has been briefly introduced one by one: Gm/r^2, and similarly, the relationship between the gravitational force of the earth and the mass of the sun and the distance of the earth from the sun can also be deduced: GM/r^2, G is the gravitational constant, so it can be seen that the earth will be in different places when it revolves, so the gravitational force of the earth at different times will be different, and only when the gravitational force of the earth and the gravitational force of the earth are balanced, the earth can rotate under the gravitational force of the sun.
In space, there is no concept of going up and down, left and right, we use the habitual thinking on the earth to think that "the earth revolves under the sun", but in fact this is wrong, the earth and other planets are around the sun, and they will never "fall".
The movement between the celestial bodies is only because the earth and other planets are gravitationally attracted by the sun, and in the same way, other planets are also gravitationally attracted by the earth, and they are all gravitational to each other, and only when the gravitational force is balanced, can they each revolve around the sun.
The key point in the orbit of an object around a planet is its velocity.
Only when an object reaches a certain velocity can it orbit the planet, and when this velocity reaches a certain value, the object can escape the planet's gravitational pull.
III. Conclusion.
The Earth has been revolving around the Sun since its birth, and this orbit is so wonderful that it makes everything come alive.
But the position of the Earth in the universe is dynamically changing, and as long as the gravitational force and speed are maintained, the Earth's orbit will not produce much "subtle change".
When humans make a difference in space and build various facilities, they need to calculate the orbits of these facilities very accurately, their velocity and gravitational equilibrium points to ensure that the equipment can operate stably.
The Earth's orbit around the Sun is an ellipse, not a complete circle, which illustrates the delicate relationship between velocity and gravitational balance.
Only by understanding these can we better explore and understand the laws of other celestial bodies in the universe.
This is also the beauty of science, which pushes people to move forward and explore the unknown.