The momentum of an apple falling to the ground is not conserved because the external force of gravity acts on it. But the momentum is conserved in a larger system. Explain? I am confused because gravity is the external force acting upward, so what's the force that is acting up on the apple? Is it air resistence? Or does it have to do with some kind of energy. I am really confused as to what the larger system is. Can someone help me figure this out? Thanks.