Friction force is the name given to the force that exists between two surfaces that are in contact to each other and that tends to oppose relative motion between the surfaces.
Friction force has both advantages and disadvantages, for example, it is the force that makes us walk . When you are walking on a very smooth surface, you are always faced with danger of slipping because smooth surfaces have reduced friction force. On the other hand, friction force causes wear and tear in machines hence need for replacement of machine parts after a period of usage. We usually applies lubrication fluids in machine joints in an attempt to reduce friction in moving machine parts. So one disadvantage of friction is that it causes costs of operation of machines be higher as it increases cost of maintenance and reduces efficiency.
How can we measure friction force?
As we have stated, friction force opposes relative motion between two objects or surfaces. For an object in contact with the ground to move, friction force between it and the ground must be overcomed. According to Newton’s law of motion, an object will remain at rest or in constant motion unless an external force acts on it. When we apply a force on such an object that is exactly equal to friction force, the object starting moving at uniform speed. If the force exceeds the friction force, the excess force causes acceleration.
By sliding different sizes of blocks made from same the material and texture across the same surface, we can be able to determine that a relationship exists between the object weight and it’s friction. This relationship is known referred to as the coefficient of friction. Coefficient of friction is defined as the ratio of the force needed to overcome friction(F) to the perpendicular force acting between the surfaces(Fn).
Coefficient of friction is given by u = F/Fn