Disappearing Beaker

Beakers have the same index of refraction as mineral oil. In a large beaker of mineral oil, hide a tiny unbroken beaker. Then take a broken piece of beaker, drop it in, and pull out the whole one. Do all of this while saying "Abracadabra!"
contributed by R. Pratt

The Ghost Flame Video Demo:

Standing waves on a string I stumbled on this demo last year while playing with a wave generator during a demo with my class. If you match a stroboscope to the frequency of the oscillator, the wave will appear to stand still. It freaks the kids out. When you difer the frequency by even 1Hz, the wave will suddenly start to move very slowly along the string. I use it to explain harmonics, frequency, and period.

Mixing Colors:

Create beats (constructive and destructive interference) using free software on a PC:

The traditional method of creating beats is to use two tuning forks of two slightly different frequencies. If you're a new teacher or just don't have a pair of suitable tuning forks for that demo, this is a decent alternative. Click here for directions. Contributed by F. Lee.

Wave Machine
Link: Wave Machine

- Duck tape
- Clamps and stands, G clamps
- Barbecue skewers
- Gummy Bears
A 5 m wave machine will require about 100 skewers and 200 gummy bears.