The shape of things

A central force is a force whose direction depends only on the distance between the point of application and a fixed point, known as central point. Hence, in a central force field, the force vector in every point is parallel to half-lines extending in every direction from the origin. For this reason, a spherically symmetric field is originated.
Gravitational attraction is a central force. Its formula is as follows:

F=G(m1*m2)/(r)2

The only vector capable of giving a direction to the force is r, the distance between the masses taken into consideration. So, for example, in the absence of other factors, from the gravitational collapse of a cloud of gas and dust, spherical bodies are created, such as the stars and planets. Actually, we know that during the formation of a celestial body, the clouds of gas and dust rotate around their centre; as a consequence, the objects produced are not perfectly spherical, but slightly flattened at the poles as a result of the centrifugal force. The Earth, for example, is not perfectly spherical but is a rotating geoid: the radius at the Equator is about 20 km less than the radius at the Poles.

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