important in:
- planet-moon systems (origin of our moon)
- formation of solar system
depends on
- mass of rotating system ( more mass => more angular momentum
- distribution of mass in system (more distant from center => more angular momentum)
- speed of rotation (faster => more angular momentum)
Angular momentum is conserved.
=> total amount of angular momentum in a system does not change.Picture this as a box of angular momentum divided into three parts. The amount of each part can change but the total size of the box never changes. This means that if on part changes, the other MUST also change in order to keep the total amount constant.
If one part changes, the other parts must change to make up for it.
Often, the total mass of the system is constant. Then we just have a trade-off between the distribution of the mass and the speed of rotation.
As the mass moves away from the center, the speed must slow down.
As the mass moves toward the center, the speed of rotation must increase.
This is why a figure skater can control the speed of a spin by moving his/her arms in close to the body or stretching them out.
[Demo: rotating platform, weights, bicycle wheel]
Here is a link to a description of the demonstration: http://www.physics.gla.ac.uk/~kskeldon/PubSci/exhibits/D1/
