I hav just begun a biomechanics unit in Year 9 Phys ed, and have recieved my assignment for the term. As part of the assignment we must consider the momentum of the ball and its forward trajectory. I didnt place this thread in homework, as there is no actual problem, just considerations. On aspect of biomechanics we must explain is throwing a softball, and the angle at which it is released. The main determining factor as to the distance which can be achieved by the throw, is gravity. My question is, if you threw the softball straight up, like 90 degrees to the horizontal, its momentum will be conserved moving the air around it with air resistance and all, but does the ball lose momentum to gravity? If so, how, as gravity does not move away from the ball, although the earth does?