Question

Reflections on concepts
1. What kinds of friction do you know and explain with suitable example? (AS)
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Answer 1

STATIC FRICTION  :

• Static friction is the force which acts between two bodies when a force is applied on a body but there is no relative motion between the surfaces.
• Static friction opposes an impending motion. It is denoted by fs.
• Law of static friction is given by :

                  fs ≤  μs × N .

• where μs  is the coefficient of static friction and depends only on the nature of the surfaces in contact. N is the normal force.

Examples : Skiing against the snow  , Creating heat by rubbing both the hands together  , Table lamp resting on the table

KINETIC FRICTION :

• Frictional force that opposes relative motion between surfaces in contact is called kinetic or sliding friction and is denoted by fk.
• It is given by:

                   

fk  = μk ×  N

• where μk  is the coefficient of kinetic friction, which depends only on the surfaces in contact and N is the normal force.

Example: When a wooden block is sliding on the floor the friction acting between the wood surface and the floor will be kinetic friction.

ROLLING FRICTION :

• Rolling friction is defined as the force which resists the motion of a ball or wheel and is the weakest types of friction.
• The coefficient of rolling friction is denoted as µr.
• The force of rolling friction is defined as the product of the coefficient of rolling friction and the normal force.
• It is given as:

                     Fs = µr × N

Examples : Rolling of the log on the ground  , Wheels of the moving vehicles

Hope this helps you ✌️✌️☘️☘️.