Friction and its Types: NCERT / CBSE Revision Notes
Friction is a force that opposes the relative motion between two surfaces of objects in contact. The force of friction always acts in a direction opposite to that of the applied force. Friction is due to irregularities on the surfaces of the objects in contact.
Factors that affect friction are:
The force of friction increases if the surfaces are pressed harder.
Types of friction are:
- Static friction
- Sliding friction
- Rolling friction
Frictional force that comes into action before the start of the motion of an object is called static friction.
When an object slides over another surface, the frictional force that comes into action is sliding friction.
When a roller rolls over a surface, the frictional force that comes into action is rolling friction.
Rolling friction is less than sliding friction, while sliding friction is less than static friction.
Friction exists between two surfaces due to:
- Irregular/uneven surfaces
- Interlocking of micro-level irregularities of two surfaces
- Ploughing of harder surfaces into smoother surfaces
Fluid friction (Drag )
Friction due to gases and liquids is called fluid friction, and is also called drag.
Friction is a necessary evil. There are instances in daily life where friction is a necessity. For example, without friction, we cannot hold objects in our hands; we cannot walk and cannot light a match stick. Examples where friction has to be minimised and not desirable is the friction between machinery parts, which causes wear and tear.