Static Friction

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

It can be explained as the force of friction which precisely balances the applied force for the duration of the stationary state of the body.

Static frictional force is a self-regulating force. i.e., static friction will at all times be equivalent and opposite to the force applied.Static FrictionR is the reaction force because of the weight W. the external force is F and fr  is the friction. F = -fr when no motion takes place.

Laws of Static Friction:

  • The maximum force of static friction is not dependent on the area of contact.
  • The maximum force of static friction is comparative to the normal force i.e., if the normal force increases, the maximum external force that the object can endure without moving, also increases.

Limiting Friction:

It is the highest value of static friction which comes into play when an object is just about to slide over the surface of a different object. For an exerted external force greater than the limiting friction, the body begins to move. Once motion has started, static friction cannot be considered. A new type of friction termed as kinetic friction comes into play

Laws of Limiting Friction:

  • The direction of limiting frictional force is always contrary to the direction of motion.
  • Limiting friction acts tangentially to the two surfaces interacting.
  • The magnitude of limiting friction is proportional to the normal reaction amidst the two surfaces.
  • The limiting friction hinges upon the material, the nature of the surfaces interacting and their evenness.
  • So long as the normal reaction is same, the magnitude of limiting friction is free of the shape or the area of the surfaces in contact, for any two given surfaces.

Stay tuned with Byju’s to learn about kinetic friction and frictional force with interesting video lectures.


Practise This Question

Those magnetic materials are best suited for making armature and transformer cores which have_____permeability and ________ hysterisis loss.