Good afternoon! 1. The Setup One block of Mass M2 is resting on top of a frictionless surface. Another block, M1, is resting on top of the of the first block. There does exist a coefficient between these two blocks, μ. 2. What happens to the bottom block when a force less than μN is applied to the top block, pushing it to the right? 3. Attempt at solution Free body diagram for M1: F to the right fs to the left M1*g downward Normal force, N1, upward Free body diagram for M2: fs to the right M2*g downward Normal force, N1, downward Normal force, N2, upward For M1, F<fsmax, so the force of friction cancels out the applied force. No x direction movement. The weight of the mass is balanced by the normal force from the block below. No y movement. For M2, the weight of the mass + the normal force from the block above is being balanced by the normal force from the frictionless surface. No y movement. The frictional force that pushes this block to the right has no pair. Acceleration of the lower block to the right is fs/M2. This does not seem to compare favorably with my intuition or my real world experiences. Can someone please care to explain what I am missing here, or would a force less than μN1 applied to the top block cause the bottom block to move to the right? The only thing I can think of is that the frictional force on the bottom block essentially becomes a new applied force, and then another frictional force between the two blocks is created that pushes the bottom block to the left and the top block to the right. This pattern repeats itself until the frictional force reaches 0. Anyone else got any input? I don't have my intro physics textbook with me currently so I cannot see if there was anything stated in there that applies to this question. Thank you all!