The force of friction is:

The force of friction is defined as a resistance force that occurs when two surfaces slide against each other. One of the fundamental principles of friction is that it is primarily determined by the normal force acting on the surfaces and the materials of those surfaces, rather than the area of contact.

When two surfaces come into contact, the microscopic roughness of the surfaces interacts in such a way that the actual area of contact at the microscopic level is far less than the apparent area. This principle demonstrates that increasing the area does not proportionally increase the frictional force. Thus, the overall friction force remains relatively unchanged as long as the normal load is constant, regardless of whether the contact area increases or decreases.

Understanding this concept is crucial when considering the design and operation of systems involving moving parts, such as refrigeration systems where friction can impact efficiency and wear. This insight into the nature of friction helps mechanics, engineers, and operators to estimate performance and make informed decisions in engineering contexts.