Whenever an object is in motion along a surface, the surface exerts contact forces on it, namely a perpendicular normal force and a parallel friction force. The frictional force always acts in the direction opposite to the relative motion between the two surfaces. The coefficient of friction, μ, is the ratio between the frictional and the normal force. A puck slides more easily on an ice floor than on a concrete floor due to the difference in coefficient of friction values. The larger the coefficient of friction value, the higher is the frictional force and vice-versa. Mathematically, the magnitude of frictional force is represented as a product of the coefficient of friction and the normal force. Thus, the frictional force is less for a smaller normal force as the area of contact between the surfaces is smaller. If normal force increases, the contact area also increases, and so does the frictional force.