Learning Friction #2

Question

A 3 kg box sits on a table where the coefficient of friction is 0.3. Calculate the friction that will oppose any motion.

Answer 1

The friction force acting on the box in motion is

f = μ_kN

where μ_k is the coefficient of kinetic friction and N is the normal force. Since the box is on a table (horizontal surface), and since the weight, mg, and the normal force N are the only forces acting along the vertical axis, Newton's second law requires

N = mg

so

f = μ_kmg

= 0.3(3kg)(9.8m/s²)

= 9 N