Left-drag your mouse up or down to raise or lower the figure’s arms and legs.
What's Going On?
This applet simulates a different view of Newton’s First Law – when an object is in motion, it tends to stay in motion. This holds for spinning motion as well!
When an object is moving in a straight line the momentum of that object is defined as its velocity times its mass. When an object is moving at a steady speed, its momentum remains constant.
For a rotating object the momentum also remains constant once it starts spinning.
If you move its legs or arms out, the speed changes since the mass of the object is redistributed. The total momentum remains the same but if the mass gets farther away from the center, the speed, as measured by angular velocity (rotational velocity), decreases, whereas the rotational inertia (moments of inertia) increases.
Looking at this mathematically angular momentum is the product of angular velocity and rotational inertia OR
Angular Momentum = Angular Velocity X Rotational Inertia
There's More!
When you see an ice skater go into a spin and pull her arms in, you can see that the spin is much faster. The big finish with arms thrown out wide is actually a way to quickly slow the skater down!
Angular momentum comes into play in launching satellites. To keep satellites from tumbling chaotically, they are given a spin. For football fans this is the same technique used to accurately throw a football.
When a satellite is in orbit, it extends antennas to communicate with the ground station. The extension of the antenna’s mass slows the satellite’s spin. In order for the satellite to spin at the correct rate, the angular momentum must be calculated in advance and the proper spin given at launch.
