Hi, Now, we know that the work done on a system equals the change of energy of that system, amd if there is no work, then the energy change must be zero. Now, suppose if I hold a stone by a string and let it drop while still holidng it so that it falls at a constant speed to the ground. My questions are: 1. Where did the potentail energy go here? it is not converted to kinetic energy as the speed is constant. To what other form of energy did it get converted to? 2. The net work done on the object is zero because the net force is zero, so there can't be any net work. The work of gravity equals my work, the net is zero work. If the work is zero, how could the energy of the stone decrease in the time no net work is applied on it? If the gravity does positive work and the potential energy decreases, then what about my negative work?