IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Find Friction Coefficient

Introduction

The maximum friction that an object can exert on the other is given by $$f=\mu_s N$$ if they do not slip on each other. The constant $$\mu_s$$ is called the coefficient of static friction between the two surfaces and depends only on the nature of surfaces. If the surfaces slip over each other the force of friction is given by $$f=\mu_k N$$ and the constant $$\mu_k$$ is called coefficient of kinetic friction. For a given pair of surfaces $$\mu_s$$ is slightly greater than $$\mu_k$$ . Here $$\mu_s$$ is obtained for two pairs of surfaces.

Apparatus

A chain, a scale, a cardboard, a block (or coin), arrangement to change inclination of the cardboard.

Procedure

Table and Chain

1. Place the chain on the table with a very small length overhanging.
2. Gently push few links to increase the length of the hanging part and keep pressing the chain with your finger at the edge of the table
3. Release the finger and see if the chain slides. If it does not, go to step-2.
4. Adjust the length of the overhanging part so that it just allows the chain to slip.
5. Measure the length $$l_0$$ of the overhanging part and the length $$l_1$$ of the total chain.
6. Calculate the friction coefficient from $$\mu=l_0/l$$.

Cardboard and block

1. Put the cardboard at certain small inclination. Place the block on it.
2. If the block does not slip, increase the inclination little bit. Keep doing this till the block just starts slipping.
3. Measure the length $$b$$ of the base and height $$h$$ of the support.

Calculate friction coefficient between the block and the cardboard by $$\mu=h/b$$.