Resonnance in wine Glasses

MATERIALS

To make a wine glass sing, you will need the following materials:

1. Wine glass - a crystal, thin-walled one works best.
2. Separate glass or jug
3. Water

PROCEDURE

To make the wine glass sing, do the following:

1. Fill the empty glass or jug with water.
2. Add the water to the wine glass
3. Wet the index or middle finger of your hand with some water.
4. Lightly rub your wet finger along the rim of the glass.
5. As you rub the glass, you will hear the "singing" sound of the glass. You may have to re-wet your finger periodically and/or adjust the pressure of your finger on the rim of the glass to keep producing the sound.
6. You can change the pitch of the sound by adding water to the glass.

EXPLANATION

Every material (such as glass, steel…) has a natural frequency at which it vibrates, called a resonant frequency. Resonance is a physical phenomenon that occurs when a body is capable of vibrating under the action of a regular force. Its period of vibration coincides with the period of vibration characteristic of that body. In these circumstances, the body vibrates increasing gradually the amplitude of vibration after each of the subsequent actions of the force.
The cup vibrates with a determinate frequency and tone. If more water is added to the wine glass the tone becomes lower.

by Mª del Mar y Blanca