what is friction?

Question

what is friction ? a defination explanation and understanding in some simple words?

Answer 1

Friction is an opposing force that acts always in the opposite direction of the applied force.

 

For instance a box pushed from point A to point B experiences a resisting force acting in the direction of the applied force(the push). That resistance is friction.

          

Friction can also be defined as the force between two surfaces.

Answer 2

Newton's 1st Law tells us that a body in motion will continue to move in a straight line at a constant speed unless acted on by a force.  Yet when we roll or slide things along a surface they do slow down and stop, so some force must be acting to stop it.  The "force" that slows down and stops the movement is friction.  Friction is a force that resists motion along or through it (in the case of air or a fluid).

 

In the case of an object sliding along a surface, the friction is proportional to the "load" or weight of the object on the surface:  F_f = μF_n  where F_f is the force of friction, F_n is the load or gravitational force (weight) of the object on the surface, and μ is a constant that's different for every type of surface (glass, metal, etc.).  Note that if the surface is slanted (inclined plane), F_n will be the force normal to the incline.

 

There are other types of friction (static, fluid, etc) but this is the basic idea.  Hope that helps.