Science | Science Experiment of the Week 9 | 295 - One Glass Musical

Water, Pitch, Tone, Notes, Xylophone, Scales - Putting different amounts of water into drinking glasses and then tapping them with a spoon to play a song.

This Week's Experiment - #295 One Glass Musical

These experiments are from Robert Krampf - The Happy Scientist

This week's experiment is an interesting variation of a very old one. Most of you have probably seen someone make a xylophone-type instrument by putting different amounts of water into drinking glasses and then tapping them with a spoon to play a song. As you will see, you don't really need all those glasses. You will need:

a tall drinking glass, made of glass
water
a spoon

Fill the glass about 1/3 with water. Hold the glass in your hand and tap it gently with the spoon. It should make a nice, musical tone. Add some water and tap it again. The sound changed, didn't it? The pitch got lower. Add more water and the pitch will get even lower. Remove some of the water and the pitch will get higher.

With the traditional experiment, you line up lots of glasses and then tune them by putting the right amount of water in each to produce the notes of a musical scale. When you tap the glass, it vibrates, producing a sound. The pitch of the sound depends on how fast the glass is vibrating. The faster it vibrates; the higher the pitch will be. Adding water to the glass slows the vibration, lowering the pitch. As you add water, more and more of the glass is in contact with the water, and the lower the pitch gets.

You don't really need all the different glasses. You just need to be able to change how high the water goes up the side of the glass. If the water reaches higher, it will absorb some of the energy, slowing the vibrations and the pitch will be lower. Fill the glass about 1/3 with water. Tap the side and listen to the tone. Now, tilt the glass so that the water reaches about halfway to the top. Tap it again. The sound is different. Tip the glass farther and the pitch will be even lower. You can even make neat sounds by tapping the glass and then quickly tilting it to make the tone drop as it is ringing.

It would be interesting to get a very tall, thin glass and put marks on the side to show how far to tilt it to produce each note. That would let you play a song by changing the tilt of the glass for each note.

This experiment ties in with several questions that I have received in the past. Several list members have noticed that when stirring a cup of coffee or tea, the sound that the spoon makes against the cup changes while the liquid is stirred. Stirring the liquid causes it to reach farther up the sides of the cup, changing the pitch of the sound. It should also work with hot chocolate, so if you live someplace where it is cold, have a cup for me. It is far too warm here in Florida for hot chocolate, but it sure does sound good right now. Have a great week.

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