1. The problem statement, all variables and given/known data The figure shows a 1.0 kg mass riding on top of a 5.0 kg mass which is attached to a spring. The 5.0 kg mass oscillates on a frictionless surface, and the spring constant is k = 50 N/m. There is friction between the upper block and the lower block, and the coefficient of static friction is 0.50. a) As the amplitude of the motion is increased, there is a maximum amplitude for which the upper block does not slip on the lower block. Explain why, and calculate this amplitude. 2. Relevant equations kx = Ffr 3. The attempt at a solution Can someone explain to me - possibly through a FBD, why, when figuring out question a), the Ffr between the 2 blocks is 6.0kg * 9.8 * .50? Why would it not be the normal force of the top box? Simply 1 * 9.8 * .5? How does the larger bottom block exert a normal force up and why does this not happen with, lets say an object lying on the earth (we dont include the mass of the earth) Thanks.