Video: Watch this demo
Description: This demonstration illustrates the principle of conservation of angular momentum (Ice skater effect).
- Rotating platform
- 2 Small dumbbell weights
- Place the Rotating platform where no one will trip over it.
- This can be done with either yourself or a student. In either case an assistant is necessary.
- Place the rotating platform on the floor and leave plenty of room on all sides for your arms (about 3 foot radius), and just in case you have to step off quickly.
- With one person holding the bottom of the platform with their foot, have the other step onto the platform.
- Have them align their body so their center of mass is right over the center of the platform, and make sure their feet are spread out.
- Give the person on the platform the two weights. Hold each weight out to the side so the hands are horizontal.
- The person on the floor should take the other’s arm, and give them a spin (not fast, but not too slow).
- The person on the platform should then bring both of their arms directly to their side, as fast as possible, and as uniformly as possible. As a variation, they may also bring their arms directly to their chest as quickly and uniformly as possible.
- If they don’t bring their arms in quick, they may loose their balance and need to step off.
- Note that they start to spin faster. This is due to angular momentum being conserved, since their weight distribution from center just changed.
- When finished, have the person on the platform bring the weights out again. Have the person on the floor bring them to rest.
- A variation of this demo is to have someone sit instead of stand. Whichever you prefer will be fine.