the force that propels the movement of the earth's gigantic rock is?

Answer 1

As our solar system started to form, all the dust, rocks and gas were fairly diffuse in space. The whole, however, was fairly massive and was therefore pulled toward a central point in the solar system. The resultant accretion formed our primordial sun. Not all the material was pulled into this sun...a small fraction of it was spun off in an ever-flattening disc of debris (think of Saturn's rings on the scale of a solar system). This debris as a whole was first spun up by the gravity of the system, and then slowly consolidated itself (most of itself) into the planets, asteroids and comets (as well as plutonian objects, Kuiper objects and various other objects) still spinning around the central sun.

Anyway, all this goes to answer your question: what keeps this "gigantic rock" (as you so eloquently described it) moving is a combination of three things...

1. the residual motion imparted to it by the formation of the solar system (otherwise known as inertia...there is no such thing as cetrifugal force)

2. gravity - the sun is massive enough to keep this big rock from flying off into space and thus puts a perpetual curve in our flight plan

3. the angular momentum of the sun - as the sun spins (fairly rapidly I might add) part of the energy of that spin is relayed to the earth (a diluted version of the slingshot effect)...interestingly enough, this continual boost actually pushes us gradually (very, very, very gradually) away from the sun, and given enough time, we might even have been able to escape altogether, except that the sun will turn into a red giant and burn us to a crisp long before that happens.

There are other forces that work to slow us down, like magnetic drag and friction, and the moon is slowly and inexorably slowing our rate of rotation, but you asked about what keeps us moving...not what is slowing us down.

Answer 2

It would be gravity of the Sun. There are a combination of things at work, but the majority of the work is being done by the Suns affect on everything in the system.

Answer 3

It is the same force that moves the earth to resist from a great force when a cosmic body pass by it. It is the moment of inertia. :)

Answer 4

pure and simple gravity. The sun's gravity is pulling the earth and every other planet in the solar system towards it. A good game to show how this works:
http://janus.astro.umd.edu/orbits/ssbuild.html

Answer 5

gravity,centrifugical