This Week's Experiment - #295 One Glass Musical
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.
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com
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