Sympathetic Vibrations

Sympathetic Vibrations

You will need: Two glasses, fine wire, water, pencil.

Pour water into a glass until it is about a third full. Tap the glass with a pencil and it will give out a musical note. Add a little more water and the note will change in tone. Fill the glass to the brim with water and tap it again-yet a different note will result. The tapping causes the sides of the glass to vibrate and make sound.

Let us return to the beginning-with our glass about one-third full of water. Take a second glass and pour a similar quantity of water into this. Tap the first glass, remember the note it gives out, and quickly tap the second glass. If there is any difference in the two notes, add water to one of the glasses until they both emit the same note when struck lightly with the pencil.

Stand the glasses about 4 or 5 inches apart and place a piece of fine wire across the top of the glass that is farthest from you. Now strike the nearest glass and you will see a slight movement of the wire on the other glass.

The wire responds to your tapping of the other glass because both glasses vibrate in sympathy. If you have adjusted the water content of each so that they emit identical notes, you will be able to make the wire on the first glass gradually move to the edge and finally fall, by tapping with your pencil on the second glass.