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The Evolution Theory of a Gear Musical Instrument

　Set the gear musical instrument in front of the students.′"what is this？"
"Gears!"，they ye11．But no one can ever guess it is actually a musicaI instru－
ment. The experiment starts off with the motor rotation．When the edge of a
business card is touched on each turning gear one by one．It makes beautiful
sounds of "do re mi fa so la ti do．"

"Boy! I can't believe it．"
It's a great surprise for the students．The good quality of the sound it pro－
duces is also attractive to them．The sound changes from that of a trumpet to a
pipe organ，a violin，etc．, in acordance with the rotation rate of the motor．
The mechanism of this machine is also simple．Because of the straight forward
indication of a positive correlation between the oscillation frequency and the
pitch of the sound it makes，it is one of experimental devices for studying sound
waves that students should not miss．Gear musical instrument have quite a long
historical background．We can find one in ”the World of sound”written byW.H.
Bragg and the significance of these devices has been pointed out．

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If you understand the essence of nature, we can make anything.
Making use of unevenness drawn up regularly, we can produce musical instrument.
It is important that we learn physics lively by ourselves.

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