Re: What keeps earth spinning at a constant rate?

    All motions keep going (forward motion, spinning etc) unless there is
something to stop slow them down.  That means if something is spinning,
it will continue to spin until something can make it change.  It turns out
that the moon creates tides on the earth.  These tides as they are dragged
over the ocean floor exert friction on the earth.  This causes the earth
spin to slow down, but only by a very small amount.  Our day lengthens by
about 0.0016 sec each century.

Reference: Discovering Astronomy 3rd ed, by Robbins, Jeffreys, and Shawl, p
169.