Friction Friction is a force which opposes the motion
of a body, when it is in relative motion. It plays an important part in our daily life.
We cannot walk on a frictionless surface. Brakes will not work if there is no friction.
Holding things, writing, grinding, igniting a match stick, all these are possible only
in the presence of friction. Here, we are studying the relationship between
force of limiting friction and normal reaction and finding the coefficient of friction between
a block and a horizontal surface by plotting a graph. Principle The limiting friction is the least force required
to move the body from rest. If F be the limiting friction and R be the
normal reaction, then (F is directly proportional to R)
(Therefore F is equal to myu R ) where (Myu) is called the coefficient of friction which
is a measure of friction based on the types of material that are in contact. Materials required: Wooden block with a hook on one side
50 or 20 gram slotted weights. Horizontal plane fitted with a frictionless
pulley at one end Spring balance
Thread Procedure Determine the mass of the wooden block, M
using a spring balance and keep it on the table top.
Tie one end of a thread with the hook of the wooden block and pass it over the pulley.
Tie the other end of the thread to the weight hanger and hang it vertically.
Increase the weights in the weight hanger till the block just starts sliding.
Note down the total mass added to the weight hanger and multiply it by acceleration due
to gravity, g, which gives the force of limiting friction, F.
The normal reaction, R is given by the mass, M of the wooden block multiplied by acceleration
due to gravity, g. The coefficient of the static friction is
then calculated by the equation (Myu is equal to F divided by R)
Repeat the experiment with different masses on the block and in each case, (myu)is calculated
and it is found to be a constant for the given pair of surfaces.
A graph is drawn with normal reaction, R along X axis and limiting friction, F along Y axis.
The graph is a straight line. The coefficient of friction is also calculated
by measuring the slope of the graph. (myu is equal to AB by OA) Applications: While walking, friction gives the required
reaction so that we can move forward or backward. Packing, tying, bandaging is possible only
due to friction. It is also the friction between the tyres
and the road that allows the car to stop while applying the brakes.