Sir,I have a query?Can you tell me which is the direction of static friction acting on us when we do run over a treadmill whena) we are at rest with respect to groundb) we are accelerating with respect to ground either in forward or in backward direction of our run.

Dear siddharth,

Static friction is the friction experienced when we try to move a stationary body on a surface, without actually causing any relative motion between the body and the surface which it is on.

It can be defined as the force of friction which exactly balances the applied force during the stationary state of the body.

Static frictional force is a self-adjusting force. i.e., the static friction will always be equal and opposite to the force applied.

Consider the figure, R is the reaction force due to the weight W. f_r is the friction and F the external force. F = -f_r when no motion occurs.

Laws of static friction

• The maximum force of static friction is independent of the area of contact.

• The maximum force of static friction is proportional to the normal force i.e., if the normal force increases, the maximum external force that the body can withstand without moving, also increases.

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