# How to determine the force of gravity on a planet, knowing the mass of the planet and the mass of the body?

It is impossible to determine the force of gravity on the planet, knowing only the mass of the planet and the mass of the body, because it is also necessary to know the radius of the planet.

Gravity is a force acting on a body from the Earth’s side and imparting an acceleration of gravity g to it:

Fg = m * g

Gravity is always directed vertically downward (toward the center of the earth).

If gravity acts on the body, then the body makes a free fall. The type of trajectory of movement depends on the direction and the modulus of the initial speed.

The value of the gravitational constant indicates that the forces of gravity between the bodies are small. They become noticeable at large values ​​of the masses of the interacting bodies. For example, the attraction of a ball to the Earth can be observed without special devices, and the attraction of the Earth to the same ball, we cannot directly observe.

The law of universal gravitation is valid for bodies whose dimensions can be neglected in comparison with the distance between them (for material points). The law is also applicable to balls, in this case the distance between the bodies is the distance between the centers of the balls.

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