LAWS OF DYNAMIC (KINETIC) FRICTION:

• The frictional force always acts tangential to the plane of contact and in the direction opposite to the impending motion.
• the frictional force is directly proportional to the normal reaction between the two contact surfaces.
• The magnitude of force of dynamic friciton bears a constant ratio to the normal reaction between the two surfaces. But the ratio is slightly less than that in case of limiting friciton.(Dynamic friction is less than static friciton).
• The frictional force remains constant for moderate speeds but it decreases slightly with the increase of speed.

LAWS OF STATIC FRICTION:

• the fricitonal force always acts tangential to the plane of contact and in the direction opposite to the impending motion.
• When the body is in limiting equilibrium, the limiting friction bears a constant ratio to the normal reaction. This ratio is called as 'coefficient of friction'.
• The coefficient of friciton depends only upon the nature of surfaces in constant and is independant of the surface areas in contact.
• The static friction is more than dynamic friction.
• Force of friciton is a self-adjusting force and it increases as the applied force increases upto limiting friction.