1. The problem statement, all variables and given/known data The board sandwiched between the other two boards in Figure P4.77 weighs 95.5N. If the coefficient of friction between the boards is 0.663, what must be the magnitude of the compression forces (assumed to be horizontal) acting on both sides of the center board to keep it from slipping? https://www.physicsforums.com/attachment.php?attachmentid=7118&d=1149969727 2. Relevant equations fs< or = usn F=ma 3. The attempt at a solution So far, I've figured out that the friction forces must cancel out the weight of the board so I did: 2F=95.5 N F=47.8N and from that I figured out the normal force is 72.1 N: 47.8 N < or = 0.663n 72.1 N < or = normal force I can't figure out how to solve for the compression forces. I assume there are two (one on each side), but I haven't a clue what my next step would be to solving it. Any input would be greatly appreciated.