Laws of Friction

1.         Laws of Static Friction

Static friction force is always equal and opposite to the net external force acting on the body.

2.         Laws of limiting friction

(i)         Limiting frictional force is independent of the apparent area of contact till the value of the normal reaction remains same.

(ii)        The direction of limiting frictional force is opposite to the direction in which one body is on the verge of starting its motion.

(iii)       The limiting frictional force depends upon the nature of surfaces in contact.

(iv)       Quantitatively, the magnitude of the force of limiting friction (F) on one of the two bodies in contact, is directly proportional to the normal reaction (R) on this body due to the other.

                        F µ R

            Or F = mR

            Where m is the constant of proportionally called coefficient of friction.

the laws of friction are:

1) It always acts in the direction opposite to the tendency of relative motion b/w two bodies

2) Its magnitude can be any <UN

3) If we consider the rotational motion, then static friction opposes the direction of net force while kinetic opposes direction of relative motion