What determines the present rotation speed of the Earth? What started
the planets spinning?
Why is the Earth subject to a wobble?
Since the mass of the Earth is changing...why not it's rotation?
Does mass/density/physical size control rotation on axis?
Why do planets spin on their axes?
Lots of good questions. Planets continue to rotate mostly because
there are very few forces that act to slow them down. None actually knows why
the planets got started spinning. Most think the material that condensed was
originally spinning and the spin was not much changed during formation of the pl anets. Wobble will
occur for any object that is not exactly a sphere. It has to do with the
natural way that any solid body moves in space if it is not spherical. As an
example try to spin a tennis racket about each of its three axes and you will fi nd some wobble about some
axes. The rotation of a planet is only changed by forces that act perpendicular
to the rotation axis (actually called torques) for a planet in space there are
not many of these. These answers are brief because of space (here). Your quest ions are good.