~ friction = force that opposes motion.
~occurs whenever 2 surfaces rub against each other.
~ has direction and magnitude.
~ friction can :
(a) prevent a statinary object from moving.
(b) slow down or stop moving object.
~the magnitude of the frictional force depends on :
(a) the nature of the surface.
*the rougher the surfaces, the greater the frictional force between them.
(b) the weight of the object.
*the heavier the object,the greater the frictional force acting on it.