# Understanding What is Angular Momentum?

Have you tried to balance your bicycle without pedaling it? You must have probably lost balance. However, once you start to pedal, the wheels start to move because of angular momentum.

Therefore, angular momentum can be defined as the property of any rotating object which is the product of the moment of inertia and angular velocity. It is a vector quantity, that is, it has both magnitude and direction.

The other ways to explain the angular momentum are either rotational momentum or moment of momentum. It is the rotational equivalent of linear momentum. Another interesting fact about angular momentum is that the total angular momentum of a closed system is zero. Therefore, it can be said that angular momentum is a conserved quantity.

## Unit and Symbol

Angular momentum is measured in terms of kg.m2.s-1. This is also the SI unit of angular momentum. The angular momentum can be denoted as . The arrow on the L shows that it is a vector quantity. The dimensional formula for angular momentum is [ML2T-1]

## Types of Angular Momentum

Angular momentum can be classified into two categories, and they are as follows:

• Spin angular momentum
• Orbital angular momentum

Spin angular momentum is defined as the angular momentum about the object’s centre of mass. Orbital angular momentum is defined as the angular momentum about the chosen centre of rotation. And the total angular momentum is given as the sum of the spin and the orbital angular momentum.

### Spin Angular Momentum

A classic example of spin angular momentum is the spinning of the top. The top is turning around the axis. An interesting fact about objects that have spin angular momentum is that it is difficult for them to get started spinning, and it is also difficult to stop them. Therefore, it can be said that the spin angular momentum depends on the moment of inertia and the angular velocity.

### Orbital Angular Momentum

The planets orbiting around the sun is a typical example of orbital angular momentum.

## Conservation of Angular Momentum

The principle of conservation of angular momentum is if the external torque acting on the body is zero, then the total vector angular momentum of a body remains constant. This statement brings us to understand what is the relation between torque and angular momentum? The rate of change of angular momentum is known as torque, and this is analogous to force. Also, the net external torque of any system is equal to the total torque on the system, that is, the sum of all internal torques of any system is zero. Examples in which the total torque of the system is zero are the rates at which the neutron stars rotate, the Coriolis effect, the spinning of a skater where the skater contracts their arms.

### Summary

• Angular momentum is the product of moment of inertia and angular velocity.
• It is a vector quantity.
• The SI unit of angular momentum is kg.m2.s-1.
• Spin angular momentum and orbital angular momentum are the two types of angular momentum.
• Angular momentum is a conserved quantity, that is, it remains constant for a closed system.
• Spinning of top, planets orbiting around the sun are examples of angular momentum.

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