In this universe, every object with a specific mass also possesses a certain gravitational force. In our solar system, 99.86% of the mass is concentrated in the Sun. Therefore, the Sun's gravitational force is exceptionally strong.
If that's the case, shouldn't the Sun pull all the other planets into itself? But instead, all the planets continue to orbit around the Sun! How is this possible? 🤔
While the Sun's gravitational force pulls all the planets toward itself, they do not fall into the Sun but instead revolve around it. This implies that there must be another force acting on these planets that counteracts the Sun's gravitational pull. That force is called the "centrifugal force".
According to "Newton's first law", when an object is moving at a constant velocity, it will not experience any change in its speed or direction unless acted upon by an external force. Furthermore, an object always tends to move in a straight line.
Therefore, when an object that would naturally travel in a straight path is influenced by the gravitational force of another object and moves along a curved path, a force acts on it to try to restore its path to a straight line. That force is called "centrifugal force."
For example, suppose you are driving a car. As the car turns around a curved path, doesn't an outward force act on you?
That force is the centrifugal force. It can be defined by the equation below.
F=mv²/r
Here r is the radius of the curved path and v is the velocity of the object moving along that path.
When planets, which would naturally move in a straight path, are influenced by the Sun's gravitational force and move along a curved path, the centrifugal force also acts on them.
The planets choose an orbital path where the Sun's gravitational force and the centrifugal force balance each other.
But why don’t they fall into the Sun and instead continue along a curved path? Now, imagine you throw a ball upwards with great speed. From your perspective, the ball goes up and comes back down along the same path, hitting the ground. But in reality, this doesn’t happen exactly as you perceive because the Earth itself is rotating, isn’t it?
So, when you throw that ball up and it comes back down, you're not standing in the same place. You've circled the center of the Earth a certain distance. And so the ball has circled with you. [Goes up a little higher]
That is, when you are on a rotating spherical system and throw a ball upwards and catch it again, the ball reaches a certain height above the sphere, rotates along with the sphere for a short time, and then returns to the ground.
If you could throw that ball to a height of about 400 kilometers above the Earth, as described earlier, the ball would first move upward and then, at a certain point, begin orbiting the Earth's surface along with it. After that, it would attempt to return to the ground. However, it would be unable to reach the ground because it would now be orbiting the Earth along with the planet itself!
Because, when it reaches its maximum height from the Earth, the ball has the velocity to fall back down. But since the Earth's gravity is weak in that area, it cannot reach the Earth's surface. Instead, it starts orbiting the Earth.
Aren’t we too revolving around the Earth while staying on its surface? The only difference is that the ball moves a little above the surface and revolves around the Earth. That’s the only distinction.
In the same way, planets orbit the Sun. When an object or planet moving in a straight path is influenced by the Sun’s gravitational force to move along a curved path, the centrifugal force begins to act on it. Even when the object reaches the minimum distance from the Sun, it cannot fall into the Sun.
This is because the object possesses the necessary tangential velocity to orbit the Sun. If the object were stationary or moving with insufficient tangential velocity at this minimum distance, it would undoubtedly be pulled into the Sun.
Since the planets has the required tangential velocity for orbiting the Sun, and the centrifugal force is also acting on it, all the planets orbit the Sun without falling into it.