Dry friction

Consider a solid block of mass m resting on a horizontal surface as shown. Assume that the contacting surfaces are rough. As we gradually increase the load, the block remains static till the load reaches a threshold value. Since the forces in the x-direction has to be balanced, it is apperent that as the magnitude of P increases from zero, the friction force also increases. Friction force, is thus, self adjusting. However, the friction force cannot increase beyond a limit. Thus there is a limiting value of friction. The maximum value of friction force, which comes into play, when the motion is impending, is known as limiting friction. When the applied force is less than the limiting friction, the body remains at rest and such frictional force is called static friction, which may have any value between zero and the limiting friction. If the value of the applied force exceeds the limiting friction, the body starts moving over the other body and the frictional resistance experienced by the body while moving is known as Dynamic friction. dynamic friction is found to be less than limiting friction. See the following animation to understand the phenomenon of dry friction.

Friction
Dry friction Consider a solid block of mass m resting on a horizontal surface as shown. Assume that the contacting surfaces are rough. As we gradually increase the load, the block remains static till the load reaches a threshold value. Since the forces in the x-direction has to be balanced, it is apperent that as the magnitude of P increases from zero, the friction force also increases. Friction force, is thus, self adjusting. However, the friction force cannot increase beyond a limit. Thus there is a limiting value of friction. The maximum value of friction force, which comes into play, when the motion is impending, is known as limiting friction. When the applied force is less than the limiting friction, the body remains at rest and such frictional force is called static friction, which may have any value between zero and the limiting friction. If the value of the applied force exceeds the limiting friction, the body starts moving over the other body and the frictional resistance experienced by the body while moving is known as Dynamic friction. dynamic friction is found to be less than limiting friction. See the following animation to understand the phenomenon of dry friction.

	Animation follows in the next slide