1. The problem statement, all variables and given/known data A little amount of sand is spilt over horizontal membrane that oscillates with frequency f=500Hz in vertical plane. If sand grains are jumping to the height h=3mm with respect to the equilibrium position, find amplitude of oscillation of membrane. 2. Relevant equations ω=2πf 3. The attempt at a solution I know that there are two forces acting on the sand when it's on the membrane, first one is gravity and the second one is force between sand and membrane. I know that at some point, sand will jump off the membrane, but i don't actually know when. Is it going to happen in the moment when membrane reaches maximum elongation (amplitude) or before and why?