Question

why the shape of maximum planets are circular???

Answer 1

Originally Answered: Why are all planets spherical?

Every object tends to be pulled towards its center of gravity. Gravitational force is weakest force among four fundamental forces of universe. So effect is not visible in the most of the objects we see around. But the object massive enough like planets and stars there gravitational pull toward center of gravity is huge enough to bind them together toward center and take minimum surface area which makes spherical shape (sphere has minimum surface area for same amount of volume). But one thing to keep in mind. This force is still not huge enough to bind it in few minutes or hours or days. But it takes millions of years to take that shape (thanks to weakest force).

But you must have heard that Earth is in the shape of tomato(bulged at equator). Now this shape is defined by the spin of Earth. Spin exerts outwards force (centrifugal). And the velocity of a point at equator is more than velocity if a point at pole. So there is more outward force at equator. Therfore the net inward force at the equator is less than that of at the pole and it makes the earth bulge at equator and take the shape of tomato. This is valid for other planets also but the shapes and quantity of deformity in spherical shape depends on speed of spin, size, density distribution and mass of planet.

Mother Nature has a rule, take the minimum surface area for the same amount of volume. And you know she is a great mathematician