Aim: To understand the nature of friction and the concept of static friction. Materials required: Toy trolley, small wooden block, inextensible string, weight hanger, weights, pulley and table. Procedure: Take a small toy trolley and keep a small wooden block on it as in the figure. Tie an inextensible string to the trolley and pass it over a pulley. And other end of the string is fixed to weight hanger. Take a small weight and keep it on weight hanger and observe the changes in motions of block and trolley.
The trolley accelerating left
Observation:
The trolley with block moves towards left with an acceleration. The block is not with respect to the surface of trolley, but it is in motion with respect to surface e table. The force of friction of the trolley acts on the direction of motion.
We increase trolley’s acceleration gradually by increasing the weight on the hanger at certain limiting weight the block comes in motion in the reverse direction.
That means now there exists relative motion between the surface of the trolley and block.
Result:
The force which opposes the relative motion of the two surfaces of bodies which are in contact is called frictional force.
The block is at rest relative to surface of the trolley upto a certain limiting acceleration. The friction exists at that stage is called static friction
