Question

A body weighing 50 N is placed on a wooden table. How much force is required to set it into motion? Coefficient of friction between the table and the body is 0.3.​

Answer 1

If the coefficient of static friction is 0.3, then the minimum force required to get it moving is equal in magnitude to the maximum static friction that can hold the body in place.

By Newton's second law,

• the net vertical force is 0, since the body doesn't move up or down, and in particular

∑ F = n - mg = n - 50 N = 0   ==>   n = 50 N

where n is the magnitude of the normal force; and

• the net horizontal force is also 0, since static friction keeps the body from moving, with

∑ F = F' - f = F' - µn = F' - 0.3 (50 N) = 0   ==>   F' = 15 N

where F' is the magnitude of the applied force, f is the magnitude of static friction, and µ is the friction coefficient.