1. The problem statement, all variables and given/known data Let's say I'm holding a crate up against the ceiling with a force of 'P', and the crate is stationary. What is the normal force? 2. Relevant equations Newton's 1st law: ƩF=0 3. The attempt at a solution I have three forces acting on the crate - The normal force, the gravitational force, and the applied force. According to Newton's first law, Fg+Fn+Fa=0 Thus, Fn=-Fg-Fa Since Fg pulls down Fg=-mg Since Fa pushes up, Fa=P Thus, Fn=mg-P However, my book says Fn=P-mg. What am I doing wrong?