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Question

i understand the cause for the planets to revolve around a star but why do they rotate?what causes them to rotate?

Answer 1

simplicity is truths best garb-its all about creation-God sent everything with momentum-every action has a reaction-the spinning motion as in a top keeps it standing up-isnt that perfection to put everything in proper motion -a big bang would simply shoot out straight where would it end-so i prayed and let Jesus into my heart to forgive my sins and be my friend-amen

but physically its all about momentum

Answer 2

There is no force that causes the planets to rotate. Most of the rotation comes about from the conservation of angular momentum. Angular momentum is given by L=m*w*r2 where m is the mass, w is the angular velocity in radians per second, and r is the radius of the circular motion. Due to conservation of angular momentum, if the radius of the orbit decreases, then its angular velocity must increase (as the mass is constant).

All planetary and stellar systems are born from the collapse of dense interstellar clouds. The clouds may originally be very large (even thousands of light years across). Consider a portion of the cloud the collapses from a size of a light year or so to the size of the solar system. That is a huge change in the size of the system. So, the very slight rotation that the cloud has in the beginning is increased dramatically when the collapse takes place. In fact, this is one of the barriers in star formation: there is excess angular momentum and there has to be a way of losing angular momentum before you can form a star.

Anyway, the bottom line is that stars like the Sun spin from the original angular momentum that was there in the solar nebula from which it formed. Not only that, all orbital motion of the planets (including the spin) is due to this orginal angular momentum.

Answer 3

Last I heard we were pretty sure why planets (and moons) did NOT rotate, but no one has done a really good job of explaining why they DO rotate, and especially why their periods differ. It is easier to explain rotation for planets with moons, as the systems revolve about the center of mass of the system and not the center of mass of the largest body.

The sun has a period of rotation of about 11 days, which matched pretty closely to the orbital period I calculated for it some years ago. Jupiter's 63 moons might well account for its 9.84 hour day, and Saturn's 56 moons might account for that planet's 10.32 hr day.

Earth has one moon and a 24 hr day. Mars has 2 small moons and has about a 25 hour day.

Answer 4

hmmmm google it