JEE Main & Advanced Physics NLM, Friction, Circular Motion Friction is a Cause of Motion

Friction is a Cause of Motion

Category : JEE Main & Advanced

It is a general misconception that friction always opposes the motion. No doubt friction opposes the motion of a moving body but in many cases it is also the cause of motion. For example :

(1) While moving, a person or vehicle pushes the ground backwards (action) and the rough surface of ground reacts and exerts a forward force due to friction which causes the motion. If there had been no friction there will be slipping and no motion.

(2) During cycling, the rear wheel moves by the force communicated to it by pedalling while front wheel moves by itself. So, when pedalling a bicycle, the force exerted by rear wheel on ground makes force of friction act on it in the forward direction (like walking). Front wheel moving by itself experience force of friction in backward direction (like rolling of a ball). [However, if pedalling is stopped both wheels move by themselves and so experience force of friction in backward direction].

(3) If a body is placed in a vehicle which is accelerating, the force of friction is the cause of motion of the body along with the vehicle (i.e., the body will remain at rest in the accelerating vehicle until \[ma<{{\mu }_{a}}mg\]). If there had been no friction between body and vehicle, the body will not move along with the vehicle.

From these examples it is clear that without friction motion cannot be started, stopped or transferred from one body to the other.  

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