Question 1

What is the relation between angular momentum and rotation about a fixed axis?

Accepted Answer

For rotation about a fixed principal axis, angular momentum is given by L = I omega. Here I is the moment of inertia about that axis and omega is angular velocity. The SI unit of angular momentum is kilogram metre squared per second.

Question 2

How does the right-hand rule show the direction of angular momentum?

Accepted Answer

Curl the fingers of your right hand in the direction of rotation. Your extended thumb points in the direction of the angular velocity and angular momentum for torque-free rotation about a principal axis. Reversing the rotation reverses L as well.

Question 3

Why does an ice skater spin faster when pulling her arms inward?

Accepted Answer

Pulling the arms inward reduces the moment of inertia because the arm masses move closer to the rotation axis. With angular momentum approximately unchanged in the ideal internal movement, omega must increase so that the product I omega remains the same.

Question 4

Why is a satellite's angular momentum conserved in a circular orbit?

Accepted Answer

The gravitational force acts toward the central body, so its line of action has zero moment about the orbital centre. For a circular orbit of radius r, the magnitude is L = mvr, and the vector is perpendicular to the orbital plane. Under a central force, both the magnitude and direction of the angular-momentum vector about the centre remain constant.

Angular Momentum Spinner 3D — Spin, Orbit and Ice-Skater

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