Dear stupid: how many times does the earth rotate in a year?

[Alex K]

I don't know what you mean by "earth's rotation being inertia". Can you elaborate?

This was taken from Universe Today ... link below ....

"Without any unbalanced forces acting on them, the inertia of the Sun and the planets have kept them spinning for billions of years.

And they’ll continue to do so until they collide with some object, billions or even trillions of years in the future."

http://www.universetoday.com/14491/why-does-the-earth-rotate/

The way I always understood it was that things just kept going after their initial evolution through inertia (a tendency to do nothing or to remain unchanged.) and nothing was actually physically acting upon them? 

I just brought it up as I thought it might have been a trick question ...

It depends on how far down the Rabbit Hole one wants go to. In Newtonian physics, the earth rotates about its axis and its parts are kept from flying away in a straight line by the forces holding together the matter, and the gravitational attraction. In Einsteinian terms, things are very complicated because gravitation is not a force and there is not much that clearly separates rotating observers from non-rotating observers. But keeping with Newtonian Physics, there are the forces binding Earth together as a Rock, and those act on its parts and let it spin about its axis as a solid body. The fact that this rotation keeps going is indeed attributable to inertia, but that still makes the resulting rotation a physical change of the body.