How does angular momentum differ from linear momentum?

Angular momentum is a measure of an object's rotation around a point, while linear momentum is a measure of an object's straight-line motion.

Angular momentum and linear momentum are both fundamental concepts in physics, but they describe different types of motion. Linear momentum, often simply referred to as momentum, is a vector quantity that depends on an object's mass and velocity. It is defined as the product of an object's mass and its velocity, and it describes the motion of the object in a straight line. For example, a car moving along a straight road has linear momentum.

On the other hand, angular momentum is a measure of the amount of rotation an object has around a certain point, often called the pivot or the axis of rotation. It depends not only on the mass and velocity of the object, but also on the shape of the object and its distance from the axis of rotation. For instance, a spinning top or a planet orbiting the sun has angular momentum.

The conservation laws for these two types of momentum are also different. The law of conservation of linear momentum states that the total linear momentum of a closed system remains constant unless acted upon by an external force. This is why, for example, if two objects collide and stick together, their combined momentum after the collision is the same as the sum of their individual momenta before the collision.

In contrast, the law of conservation of angular momentum states that the total angular momentum of a closed system remains constant unless acted upon by an external torque. This is why, for example, a spinning ice skater can change her speed of rotation by pulling her arms in or out - she is changing her body's distribution of mass, and hence its moment of inertia, but her total angular momentum remains constant.