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Sound Production by Moving Object
Name: Alivia
Status: student
Grade: K-3
Location: OH
Country: N/A
Date: 8/10/2005
Question:
Why does a stick make that noise when you whip it through
the air?
Replies:
Alivia,
EVERY sound is vibrations passing through the air. A vibrating rubber band,
a vibrating speaker, clapped hands, all sound sources work by causing the
air around them to vibrate. These air molecules, moving forward and
backward, bang against other molecules. The vibration pattern travels
through the air until it reaches your eardrum. This causes your eardrum to
vibrate with the same pattern. Now you hear a sound.
If the vibrations are too infrequent (an extremely low pitch) your ear
cannot hear
it. This is what most moving sticks produce when they push the air around
them. If the stick moves fast enough, the air around the stick gets a
faster vibration, a pitch your ear can hear. In fact, the faster you move
the stick, the higher the pitch you produce.
Dr. Ken Mellendorf
Physics Instructor
Illinois Central College
Very "simple" question!! Very complicated answer!! Whirling a stick
through air the stick can vibrate in very complicated patterns depending
upon its size, shape and its composition. In addition, the stick causes
the air through which it moves to flow in very complicated ways, called
"turbulent" flow. This sets up regions of high pressure and low pressure
in surrounding air. When the pressure equalizes, sound is produced. A loud
example is when a balloon "pops". The "rumble" you hear when a car is
moving is another example.
Vince Calder
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Update: June 2012
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