Angular momentum facts for kids
The angular momentum (L) of an object rotating about an axis is the product of its moment of inertia and its angular velocity:
where
 is the moment of inertia (resistance to angular acceleration or deceleration, equal to the product of the mass and the square of its perpendicular distance from the axis of rotation);
 is the angular velocity.
Angular momentum is a conserved quantity—an object's angular momentum stays constant unless an external torque acts on it.
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Images for kids

This gyroscope remains upright while spinning due to the conservation of its angular momentum.

Velocity of the particle m with respect to the origin O can be resolved into components parallel to (v//) and perpendicular to (v⊥) the radius vector r. The angular momentum of m is proportional to the perpendicular component v⊥ of the velocity, or equivalently, to the perpendicular distance r⊥ from the origin.

Moment of inertia (shown here), and therefore angular momentum, is different for every possible configuration of mass and axis of rotation.

In this standing wave on a circular string, the circle is broken into exactly 8 wavelengths. A standing wave like this can have 0,1,2, or any integer number of wavelengths around the circle, but it cannot have a noninteger number of wavelengths like 8.3. In quantum mechanics, angular momentum is quantized for a similar reason.