# Torque

## Explanation

Torque is defined as a turning or rotating force that makes the object rotate about a fixed axis. A good example for torque is a human spinning a bicycle wheel around its axis by applying a force on its outer surface. The force applied on the outer tire multiplied by the radius of the wheel from its centre of mass gives the torque. Torque is denoted by the symbol τ. It is measured in SI units as newton metre Nm.

### How is torque different from work?

Though torque and work have same units of newton metre, they are totally different entities. Work is defined as the amount of energy needed to translate an object through a certain distance by applying a force on it. On the other hand, torque is a force applied on an object at a certain distance from its centre of mass, which spins the object about an axis. The rotational counterpart for work is actually known as rotational work, which is defined as the amount of energy required in applying a torque to rotate an object through a certain angle.

### How is rotational work calculated?

For a translational system, the work done W can be simply expressed as the energy needed to apply a force in a certain direction F to move an object over a certain distance d.

W = F × d

For a rotational system, the same can be expressed as the energy needed to apply a constant torque τ to rotate the object through a particular angle θ.

Wrotational = τ × θ

### What is the difference between static torque and dynamic torque?

Static torque is the force applied to a rotational object where the angular velocity of it is constant, and no angular acceleration or deceleration is involved. On the contrary, a dynamic torque is a force applied to the rotational system where it accelerates over time.