Category :
8th Class
Friction
Synopsis
- Friction opposes the relative motion between two surfaces in contact. It acts on both the surfaces.
- Friction depends on the following factors:
- Material of the bodies in contact.
- Roughness of the two surfaces in contact. The rougher the surfaces, the greater is the friction.
- The force of friction is independent of the area of the two surfaces in contact.
- The force of friction between two bodies is parallel to the contact surface and always opposite in direction to that of the relative motion.
- Although friction is undesirable, it is important for activities like sitting, walking, braking, etc.
- Friction in machines is reduced by using lubricants and smoothening the surfaces in contact (polishing).
- Harmful effects of friction:
It increases wear and tear
It produces heat
It decreases efficiency
- The static friction (or limiting friction) is the friction between any two bodies when one of the bodies just tends to move or slip over the surface of another body. There is no actual movement of the body in static friction.
- Sliding friction (or dynamic friction) comes into play when one of the bodies slides over the other.
- When a body (like a roller or a wheel) rolls over the surface of another body (e.g., road surface), the friction is called rolling friction.
- Rolling friction is much less than sliding friction.
- Liquids and gases (fluids) exert much less friction as compared to solids.
- The frictional force exerted by fluids (including air) is called drag.
- The special shape of a body (object) to reduce drag is called streamlined shape. For e.g./birds and aeroplanes have streamlined shapes.
- Air also exerts friction on a moving body, but it is much smaller as compared to solids and liquids.
