Principles of Friction
- Sonam Shivam
- Feb 2, 2017
- 2 min read
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other.
TYPES OF FRICTION :
Friction is of the following two types -
1) Static friction
2) Dynamic friction
STATIC FRICTION - It is the friction experienced by a body, when it is at rest. In other words, it is the friction when the body tends to move.
DYNAMIC FRICTION - It is the friction, experienced by a body when when it is in motion. It is also called kinetic friction. The dynamic friction is of the following two types :
1) Sliding friction : It is the friction, experienced by a body when it slides over another body.
2) Rolling friction : It is the friction, experienced by a body when it rolls over the other. In other words, when balls or rollers are interposed between the two surfaces.
LIMITING FRICTION : There is a limit beyond which the force of friction cannot increase. If the applied force exceeds this limit , the force of friction cannot balance it and the body begins to move, in the direction of the applied force. This maximum value of frictional force, which comes into play when a body just begins to slide over the surface of the other body, is known as limiting friction.
It may be noted that when the applied force is less than limiting friction, the body remains at rest, and the friction is called static friction, which may have any value between zero and limiting friction.
LAWS OF FRICTION :
Prof. Coulomb, after extensive experiments, gave some laws of friction, which may be grouped under the following heads :
1) Laws of static friction
2) Laws of kinetic or dynamic friction
Laws of Static friction -
Following are the laws of static friction :
1) The force of friction always acts in a direction, opposite to that in which the body tends to move, if the force of friction would have been absent.
2) The magnitude of the force of friction is exactly equal to the force which tends to move the body.
3) The magnitude of the limiting friction bears a constant ratio to the the normal reaction between the two surfaces. Mathematically :
F/R = constant
where, F = limiting friction
R = Normal reaction
4) The force of friction is independent of the area of contact between the two surfaces.
5) The force of friction depends on the roughness of the surface.
Laws of Kinetic or Dynamic friction -
Following are the laws of kinetic or dynamic friction :
1) The force of friction always acts in a direction, opposite to that in which the body is moving.
2) The magnitude of kinetic friction bears a constant ratio to the normal reaction between the two surfaces. But this ratio is slightly less than that in case of limiting friction.
3) For moderate speeds, the force of friction remains constant. But it decreases slightly with the increase of speed.
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