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- The fundamental equation defining the coefficient of sliding friction is m=f/N. In this equation, m is the coefficient of sliding friction, f is the force of friction, and N is the normal force. The force due to friction is the amount of force resisting the movement. The normal force is the force holding the two surfaces together.
- In order to figure out the coefficient of friction, it is necessary to know what the normal force is. If one of the surfaces sliding against each other is lying flat on top of the other, on flat ground, then the normal force is simply the weight, which is the force of gravity, of the object on top. If the object on top is being pressed onto the object on the bottom and both are on flat ground, then the normal force is just the weight of the object on top plus the force of the push.
- If the two objects are not on flat ground but instead on a slope, then figuring out the normal force is more complicated. In this case, the normal force is the component of the force holding the objects together that is at right angles to the slope. The formula N=F(cos(a)) will give you the normal force in this case. Here, F is the vertical force holding the object together. This is usually the weight of the top object, as in the previous examples. The angle of the slope is a, and the cosine of a multiplied by the force holding them together gives the normal force.
- Once you have figured out the normal force, all you need to do to figure out the coefficient of sliding friction is find the force due to friction. There is no one way for determining this. If you are trying to solve a problem in physics class, this value may be given to you as part of the problem. If you are trying to figure out for yourself what the coefficient of sliding friction between two surfaces is, then you need to measure the force or figure it out for yourself.
Coefficient Equation
Normal Force
Normal Force Equation
Friction Force
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