Why do planets have to rotate on their own axis?
The origin of celestial bodies like the stars and the planets is from large clouds of gases called nebulae. There are no forces acting within or between celestial bodies that makes them rotate. Unlike revolution around a star, which is essential to keep a planet from collapsing into the star, rotation on its own axis is not essential.
The reason why planets rotate is that the nebulae they are created from rotate at a negligible speed. But as the gases collapse from clouds that are thousands of light years large into a dense mass which is a few thousand kilometers in radius, to conserve angular momentum, the rate of rotation has to increase by a large extent.
The rotation creates centrifugal forces which have to be balanced by the gravitational force of attraction between all the particles making up the planets. Once this happens the planets continue to rotate at the equilibrium velocity as there is no force which opposes this rotation.
Ya! You are correct.
Planets rotate at different rates. One day is defined as how long it takes Earth to rotate once. Jupiter and Saturn spin much faster, in only about 10 hours. Venus rotates much slower, in about 243 Earth days.
Most planets rotate in the same direction in which they revolve around the sun, with their axis of rotation standing upright from their orbital path. A law of physics holds that such rotation does not change by itself.
Planets become larger and larger as their materials coalesce out of the accretion disks of rubble and dust that form them, and crash into the growing body. Materials falling out of the disk don't fall directly into the body, but tend to make glancing blows, or go into rapidly decaying low orbits for a while. The disk material orbits the sun, because material that wasn't going fast enough to orbit crashed toward the sun. The orbiting material farther out from the sun is moving a little more rapidly than material between the body and the sun. So the material falling toward the body from the night side imparts more rotational energy when it hits, adding to the rotation of the body.
The planets rotate on its own axis because of gravity. If there was not enoght gravity. The planets would float anywhere if there was not gravity it is because of gravity that the planets move on there own axis.