why are the planets nearly spherical,not triangle, square?why and how the planets rotate?

Answer 1

Exactly the same reason why you can't have square or triangular soap bubbles. Gravity forces all the planetary material into a shape that has the smallest surface area for the greatest volume.

Answer 2

Well... Gravity, and a little process called accretion..

In the beginning was the gas... And the gas was good - And there were rocks in the gas...

And eventually some rocks and gas that loved each other very much decided to come together to form a planetissimal... And then others joined the merry cosmic dance.

And as the accretion disc spun, yea though it imparted it's spin onto the planetissimals by both friction and impact..

And inertia looked upon the disc and proclaimed it good..

Faster the minor planets spun and heavier they became and they took on the mantle of squashed spheres, for that was the shape intended for them by both the strong gravitic and centifugal force.

And verily, pieces of the disc too big to be accreted were captured, and they did serve the fledgling planets as moons. Twinkling diadems that served to impart tides and sources of wonder for the inhabitants of the planets.

And slowly, gravitic braking took hold of some of these 'moons' to make it so that their same sides pointed towards the planets.

And that's why most things spin, and why they're spheres

Answer 3

If a body was small enough it could take on any of these shapes but as they became more massive gravity would sculpt them till eventually they would be quite spherical.
A planet has the ability to not rotate but is is likely some residual angular momentum would produce a rotation around a particular axis.

Answer 4

Planets are thought to have formed either by accretion or by being cooled and solidified globules of matter.
The sphere is the geometric shape which can contain the most mass for its surface area so most planets are nearly that, at least if they are big enough to be planets.
They rotate because everything in the universe moves and the angular momentum is probably left over from the original formation and possibly assisted by various interacting gravitational fields.

Answer 5

Gravity

Answer 6

Gravitational accretion tends to form spherical objects.

Doug

Answer 7

bcoz of gravity of d planets pulling d mass toward inside.