So apparently there's more to dropping a ball than just gravity... who would have thought?! Well, for starters, when the ball is above the ground it has potential energy, due to the equation U = mgh. (See? Gravity is key!) As the ball comes closer and closer to the ground though, that potential energy is steadily converted to kinetic energy in the form of velocity (k = .5mv^2). Since m is in both equations, the mass of the object does not affect how fast the ball falls nor the time it takes the ball to fall. HOWEVER, an important thing we learned in Physics C this year is that not all of the potential energy is converted to kinetic energy, due to the fact that a drag force acts against the object falling. This drag force creates friction, which heats up the object, and that heat accounts for the "lost" energy. So that is the physics of dropping a ball, although, as I previously stated, it can really be summed up by this: gravity.