Singing Glasses Toothpick Mover

Materials

• two wine glasses

• a pitcher of water

• a toothpick

The experiment

1. Partially fill each glass with water.

NOTE: If the glasses are identical, it works best to fill them each half full; if the glasses are different, you’ll need to experiment with the levels of water to determine what works best. (see step 4)

2. Hold the stem of the glass with one hand and dip the index finger of your other hand into the water.

3. Rest your wet finger on the rim of the glass, press down slightly, and rub it all the way around the rim without stopping. Keep going in a circular motion around the lip of the glass while maintaining the pressure, and, in almost no time, you’ll hear a high pitched whistling sound.

4. Once you’ve mastered the art of making the wine glass sing, do the same thing with the other wine glass. You want the pitch from each wine glass to be the same. This means that you will need to adjust the amount of water in each glass until the pitch is the same. If you have wine glasses of identical sizes, then matching the water levels will match the pitch. If the wine glasses are not the same size, you will have to listen carefully and adjust the water level so that the pitch matches.

5. Now that the pitch is the same between the two wine glasses, it’s time for the fun part. Rest a stick match or toothpick on the rim of one of the glasses. Position the second wine glass close to the first one, but make sure they’re not touching. Dip your finger in the water and make the glass without the match sing. Don’t take your eyes off the stick match or toothpick. What? It moves! How does that work?

How does it work?

There are really two parts to this activity… the singing of the wine glass and the movement of the match.

Let’s discuss the singing wine glass first. As you rub your finger on the rim, your finger first sticks to the glass and then slides. This stick and slide action occurs in very short lengths and produces a vibration inside the glass, which in turn produces a sound. As soon as the first few vibrations are produced, the glass resonates. That means you’re causing the water in the glass to vibrate and create one clear tone. You can change the pitch (highness or lowness of the sound) by adding to or subtracting from the amount of water in the glass. The volume (loud or quiet) can be changed only a little bit by increasing or decreasing the pressure from your finger.

Now, about the movement of the match… this is caused by a sympathetic vibration. Because you’ve made sure both glasses vibrate at exactly the same frequency, the sound waves produced by the first glass travel in every direction. When those sound waves reach the second glass, the glass begins to vibrate as well and the match moves. Telekinesis? Nope… just some really clever science.

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