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

# The Law of Lever

## Objective

To explore quantitatively the relation between the effort and load in levers.

## Introduction

A small effort but a longer effort arm lifts a heavy weight. The product of the effort and arm length should be equal on two sides.

## Apparatus

foot ruler, identical coins, a pencil

## Procedure

Balance the ruler across a pencil. Put 3–4 coins at any point on one side of the ruler. Balance it by placing same number of coins on the other side. Note the point where balance occurs. Are both points equidistant from the pencil?

Place one coin on one side of the ruler. Try balancing it by placing two coins at various points on other side of the ruler. Measure the distance of both points from the pencil. Repeat the above exercise with one coin on one side and three coins on other side. Do you find any relation between the number of coins and their distance from the pencil?

## Discussion

Let $$W_1$$ be weight of the coins placed at distance $$x_1$$ from the pencil and $$W_2$$ be weight of the coins placed on the other side of pencil at a distance $$x_2$$ (see figure). The product of weight and distance on one side should be equal to the product of weight and distance on the other side i.e., $$W_1 x_1=W_2 x_2$$. The product of the force and arm length is called moment or torque.