Angular Momentum of a Particle – Class 11 | Chapter – 7 | Physics Short Notes Series PDF for NEET & JEE

Angular Momentum of a Particle: Angular momentum is a measure of the rotational motion of an object. For a single particle, the angular momentum is defined as the cross product of its position vector and its linear momentum vector:

L = r × p


  • L is the angular momentum
  • r is the position vector of the particle relative to a chosen axis of rotation
  • p is the linear momentum of the particle.

The direction of the angular momentum vector is perpendicular to the plane formed by the position and momentum vectors, according to the right-hand rule. The magnitude of the angular momentum vector is given by:

|L| = r * p * sin(theta)


  • theta is the angle between the position and momentum vectors.

The angular momentum of a particle is conserved if the net torque acting on the particle is zero. This is known as the law of conservation of angular momentum.

Importance of Angular Momentum of a Particle

The angular momentum of a particle is an important concept in physics and has many applications in various fields. Here are some of the key importance of angular momentum of a particle:

  • Conservation of Angular Momentum: One of the most important aspects of angular momentum is the conservation of angular momentum principle. According to this principle, the total angular momentum of an isolated system remains constant unless an external torque acts on the system. This principle has important implications in a wide range of fields, including mechanics, electromagnetism, quantum mechanics, and astrophysics.
  • Understanding of Rotational Motion: Angular momentum is a fundamental concept in the study of rotational motion. It helps to explain the behavior of objects that are rotating or spinning, such as planets, stars, and gyroscopes. Understanding the properties of angular momentum is essential to understanding the mechanics of these systems and their behavior.
  • Gyroscopic Effects: Gyroscopes are devices that use the principle of angular momentum to maintain stability and control. They are used in a wide range of applications, including navigation, aviation, and spaceflight. The gyroscopic effect arises from the conservation of angular momentum, and the design of gyroscopes relies heavily on the principles of angular momentum.
  • Atomic and Molecular Physics: Angular momentum is also important in the study of atomic and molecular physics. The angular momentum of electrons in atoms and molecules plays a crucial role in determining their energy levels and behavior. Understanding the principles of angular momentum is essential to understanding the properties of matter at the atomic and molecular level.
  • Quantum Mechanics: Angular momentum is a key concept in quantum mechanics, where it is used to describe the properties of subatomic particles, such as electrons and protons. The principles of angular momentum are central to understanding the behavior of these particles and their interactions with each other.

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By Team Learning Mantras