1. The problem statement, all variables and given/known data from the free body diagram of a block resting on a flat surface, I am trying to derive the coefficient of static friction. 2. Relevant equations 3. The attempt at a solution I have the definition of the coefficient as: us=Fn/Ffr But in my free body diagram i am pulling on the block, which resists with the Ffr I have [tex]\Sigma[/tex]Fx=0 F-Ffrus=0 us=F/Ffr My confusion is because if the definition of the coefficient is above, why don't I derive it when I observe my free body diagram of the block. What am I missing? The forces in the x direction are my pulling force and the friction force that resists it * us How do i get the weight of the block into my derived equation?