Trusses, Frames and Machines: Frequently Asked Questions

Friction is a resistance force that opposes the slipping motion of

a body relative to another body with which it is in contact
a body relative to the surface with which it is in contact

Q2. What are the basic characteristics of friction?

Q3. Is there more than one kind of friction?

Static friction is the maximum friction force that can be developed at the surface of contact. It can be viewed as the maximum resistance force to the impending sliding or slipping motion of the body. If the motion-inducing force component is greater than the static friction force at the surface of contact, the body will begin to slide. As soon as sliding begins, friction force drops to a lower level called the kinetic friction. The static and kinetic friction forces are related to the normal force at the surface of contact as well as the static and kinetic coefficients of friction, respectively.

Static Friction: equation

Kinetic Friction: equation

No! This is not always the case. This relationship is reserved for two specific cases. In the first case, when sliding motion is impending, equation , and when the body has begun to slip, . In any other situation, F and N are independent of each other. Therefore, one should not use without validating the governing assumption.