Calculus-based physics....mechanics I'm having a little trouble with this problem... "A small glass ball is projected straight up in an evacuated tube (no air resistance) and then falls back down. During its motion it passed both an upper and a lower timer that are separted by a distance H. Let TsubL be the time interval between the two passes across the lower timer, and TsubU be the time interval between the two passages across the upper timer. Find an expression for the acceleration of gravity, g, in terms of H, TsubL, and TsubU. Any help would be appreciated, but thorough explanation would be a plus. Thanks everybody.