# The Coefficient of Friction

The coefficient of friction is a dimensionless scalar value which describes the ratio of the force of friction between two bodies and the force pressing them together.

The coefficient of friction between the tires of a car and the road varies depending on the road conditions. This affects the stopping distance of the car.

The equation for finding the coefficient of friction is:

u = Fr/Fn

Where:
u = coefficient of friction
Fr = force required to move the object
Fn = force normal, or the perpendicular weight of an object acting on a surface

The coefficient of friction varies with acceleration. Fr = ma, where m = the weight of the object, and a = acceleration. Therefore, the equation for finding the coefficient of friction can also be written as

u = (m x a)/Fn

The figures m and Fn are constant values, and a is the only variable. Due to this, if the acceleration has a higher value, the coefficient of friction is higher, and if the acceleration has a lower value, the coefficient of friction is lower. On wet roads, the acceleration is lower, and so the coefficient of friction will be lower. The acceleration is equal to the deceleration, hence making the deceleration lower and increasing the stopping distance of moving vehicle. Icy roads are more slippery than wet roads, so the acceleration and deceleration on a wet road would be even lower and further increasing the stopping distance of a moving vehicle.