Introduction To Torque And Its Applications

What is Torque?

Torque is the measure of how much a force acting on an object causes that object to rotate. We can define torque as:

The rotational equivalent of linear force

It is the twisting force that tends to cause rotation. The point where the object rotates is called the axis of rotation. In physics, torque is simply the tendency of a force to turn or twist.

Common symbols τ, M
SI unit N⋅m
In SI base units kg⋅m2⋅s−2
Dimension M L2T−2
Other units pound-force-feet, lbf⋅inch


To explain torque in detail let us consider the 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, thus 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 a 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.

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.

Now, 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 Measurement

Measurement of Torque

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.

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Examples of Torque

Let us consider the situation given below:
Examples of Torque
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.

Applications of Torque

In any object experiencing torque, there is a pivot point. Some applications are provided below:

  • Seesaws and Wrenches
  • Gyroscopes
  • A pendulum or a parachute is applying torque when swinging
  • A person riding a bicycle
  • Flag flying on a mast

Frequently Asked Questions on Torque

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.

Is torque energy?

No, torque is not energy.

How does torque differ from force?

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

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