Angular momentum

Definition

Angular momentum is the rotational analog of linear momentum, representing the quantity of rotation of an object. It is a vector quantity given by the product of an object's moment of inertia and its angular velocity.

5 Must Know Facts For Your Next Test

1. Angular momentum ($\mathbf{L}$) is calculated as $\mathbf{L} = I \mathbf{\omega}$, where $I$ is the moment of inertia and $\mathbf{\omega}$ is the angular velocity.
2. In a closed system with no external torques, angular momentum is conserved.
3. The SI unit for angular momentum is kilogram meter squared per second (kg⋅m²/s).
4. The direction of angular momentum follows the right-hand rule: curl your fingers in the direction of rotation, and your thumb points in the direction of $\mathbf{L}$.
5. Torque ($\tau$) causes changes in angular momentum and is related by $\tau = \frac{d\mathbf{L}}{dt}$.

Review Questions

• How do you calculate angular momentum for a rotating object?
• What happens to the angular momentum in a system with no external torques?
• Which rule helps determine the direction of angular momentum?

Related terms

Moment of Inertia: A measure of an object's resistance to changes in its rotation rate, dependent on mass distribution relative to the axis.

Torque: A force that causes an object to rotate about an axis; it can change an object's angular momentum.

Conservation of Angular Momentum: $\text{A principle stating that if no external torque acts on a system, its total angular momentum remains constant.}$