What force causes warm molten rock to move upward in the mantle?
a. convection
c. refraction
b. radiation
d. conduction

The answer is A. Convection.

Warm air is less dense than cold air. In something like a room heated by a fireplace, the warm air is pushed up by colder air. It's then cooled and comes back down. The same principle applies to molten rock in the mantle. Slightly cooler pockets push up the warmer ones.

It is called convectiojn zones

If there was no gravity then their would be no downword force on the football to have it return the the grownd, and if there was no friction (mainly air friction) then there would be no opposing force the stop the ball from moving through the air allowing the ball to travle ∞.