Introduction To Torque And Its Applications

To understand what is torque let’s consider the following figure:


We can see that the net force on the body is zero. Hence the body is in translational equilibrium. But the rod tends to rotate, this turning effect produced by force is known as moment of force or torque. Now we will consider the example of a door and try to formulate the equation for torque.
If we apply force closer to the hinge, then larger force is required to rotate the door. Also, it depends on the direction in which the force is being applied. If it is perpendicular to the line joining the hinge and the point of application of force then smaller force is required. So from above observation, we conclude that torque produced depends on the magnitude of the force and the perpendicular distance between the point about which torque is calculated and the point of application of force. So mathematically it is represented as:

τ = F.r. sinθ

Torque Unit

Unit of torque is Newton – meter (N-m). The above equation can be represented as the vector product of force and position vector.

τ = r x F

So as it is a vector product hence torque also must be a vector. Using vector product notations we can find the direction of torque. We will consider an example to see how to calculate torque.
Consider the situation given below:



In the above Example:
F = 5N
r = 4m
Sinθ = 30°

Putting these values we have,
τ = 5 x 4 x Sin 30°
τ = 10 N-m

Some of the real life examples involving torque are that of a see – saw or in automobiles engine. So next time when you see around just notice things which are working on torque. We have just started our journey to learn rotational motion and translational motion. So sit back and enjoy learning with interesting video lectures.

Practise This Question

For the given uniform square lamina ABCD, whose centre is O,