Introduction To Torque And Its Applications

What is Torque?

We can define torque as the measure of how much a force acting on an object causes that object to rotate. It is the twisting force that tends to cause rotation. The point where the object rotates is called as the axis of rotation. In physics, torque is simply the tendency of a force to turn or twist.

To explain torque in details let us consider the figure given below.


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.

Torque Formula

From the 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 torque 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.

Examples Of Torque

Let us consider the situation given below:


In the above diagram:

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 go out just notice things which are working on torque principle. We have just started our journey to learn rotational motion and translational motion. So sit back and enjoy learning with interesting video lessons.

Important Questions Asked From Torque

Q.1) What is a torque in physics?

We can define torque as the twisting force that tends to cause rotation.

Q.2) What is the difference between torque and moment?

Torque is a special case of Moment, such that it relates to the axis of the rotation driving the rotation. Whereas moment relates to being driven by an external force to cause the rotation.

Q.3) How do you define torque?

[Refer to Question Number 1]

Q.4) Is torque a energy?

Torque is not energy.

Q.5) What does torque do?

Torque measures the “turning ability” of an engine.

Q.6) What is torque or turning force?

[Refer to Question Number 1]

Q.7) How is torque calculated?

A simple way to calculate the magnitude of the torque is to first determine the lever arm and then multiply it times the applied force.

Q.8) How does torque differ from force?

Force has units of Newtons, while torque, being the product of a force and a distance, has units of Newton ⋅ meters.

Q.9) Why is torque so important?

Torque is what helps spin the crankshaft to help provide power to the vehicle.

Q.10) What is Torque in simple terms?

[Refer to Question Number 1]

Q.11) How does a torque work?

Torque is the amount of “turning power” you have.

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Practise This Question

A ring of radius R, made of an insulating material carries a charge Q uniformly distributed on it. If the ring rotates about the axis passing through its centre and normal to plane of the ring with constant angular speed  ω, then the magnitude of the magnetic moment of the ring will be?