#PZP221 In the system of the rain drop it is being accelerated by the force of gravity exerted on it by the Earth. This changes the raindrop's kinetic energy. Because the Earth is not part of the system the energy change is the work done on the system by the Earth.
@ProfZirul#PZ221 my bottle is undergoing rotational acceleration and linear acceleration when I rotate it with my hand. I'm adding torque to the bottle with my hand causing it to accelerate its rotations as it rotates it is accelerating on a linear plane as it moves across my desk.
@ProfZirul#PZ221 ...in this video the pumpkin, Earth, and the table are a system. When my hand pushes on the pumpkin and accelerates it from rest it does work on the pumpkin.
@ProfZirul If my rollerblades are a system in themselves then if I were to push them and they fell over I'd be contributing energy to the system from the outside. Which is described as the impulse. #PZ221