Friction


The motion of a body sliding over another body is restricted by a force. That force is known as friction.

This force arises from the fact that the surfaces, although planned and created swish, have ridges and depressions that interlock and therefore the relative movement is restricted.

friction sparks
Friction sparks

Thus, the force of friction on a body is parallel to the slippery surfaces and acts within the direction opposite to it of the slippery body.


There square measure phenomena, wherever it’s necessary to scale back the force of friction whereas in some cases it should be multiplied. In the case of shaper slides, journal bearings, etcetera, wherever the facility transmitted is reduced thanks to friction; it’s to be shriveled by the employment of greased surfaces.

In processes, wherever the facility is transmitted through friction, it makes an attempt square measure created to extend it to transmit additional power. For example Clutches and belt drives.


Even the tightness of a nut and bolt depends in the main on the force of friction. Had there been no friction between the nut and therefore the surface on that it’s tightened, the nut would loosen off at the instant the wrench is removed.


Kinds of Friction


· Dry Friction: Dry friction is said to occur when there is relative motion between two completely- lubricated surfaces. It is further divided into two types:

Solid Friction: When the two surfaces have a sliding motion relative to each other, it is called solid friction.

Rolling Friction

Friction due to rolling of one surface over another (For Example Ball, Roller Bearings, etcetera) is called rolling friction.


Skin Friction or Greasy Friction

When the two surfaces in contact have a minute thin layer of lubricant between them, it is known as skin friction or greasy friction Higher spots on the surface break through the material and is available in-tuned with the opposite surface.


Film Friction

once the 2 surfaces in-tuned area unit fully separated by material, friction can occur because of the cutting of various layers of the material. This is referred to as film friction or viscous friction.

Go to the next topic Gears and Gear Trains | This page is the part of Free online course Theory of Machine

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