Conservation Of Angular Momentum

This demonstration has a couple components. A bicycle wheel is mounted on an aluminum shaft, with copper wire wound around the rim to increase its moment of inertia. There's a modified stool, which has had footrests welded on and sits on a large bearing mounted to a wooden base.

Demonstrate how conservation of angular momentum affects the motion and rotation of objects.

• Rotating stool
• 2kg-5kg weights (as heavy as you can hold at arms length with one arm)
• Weighted Bicycle wheel with handles

• Set the stool in a safe location, at least arms-length from anything which may get in the way.

• With the stool stationary, sit on it and attempt to rotate the stool by moving your arms around with the weights held in your hands. This will be impossible. (Practically, as long as you neglect the small friction in the bearing.)

• With the weights held out from the body get an assistant to rotate the stool slowly. The stool will speed up noticeably as the weights are brought towards the body.

• Now hold the bicycle wheel with the shaft vertical. IF you then rotate the wheel by hand, the stool will begin spinning in the opposite direction so that the net angular momentum of the system is zero.

• Hold the wheel vertical and set up a slow rotation on the stool. This slow rotation can be cancelled out by spinning the wheel yourself in the appropriate direction.

• Have an assistant hand the rotating bicycle wheel to the student on the stool, holding the shaft vertical. If the student now inverts the wheel in front of themselves a compensating angular momentum of the stool will occur noticeably. Alternatively, hand it to the student so that they hold it horizontally in front of themselves as though they're holding the handle bars of a bike. The student can then 'steer' themselves by turning the axis of the wheel towards vertical in either direction.

This demonstration has minor hazards in the form of the spinning wheel and the stool. Spinning yourself too fast can lead to loss of balance and injury. The wheel, if spun at a speed, can also be dangerous. The rim of the wheel could scrape skin and getting a finger caught in the spokes would be quite unpleasant. Take the necessary precautions!