This Week's Experiment - #223 Simple Quacks
It has been a while since I did an experiment on sound, and quite a while
since we did one that lets you make annoying sounds. To correct that, we are
going to make a "quacker" and along the way, learn some science. You will
need:
a plastic, drinking straw
scissors
The first thing you need to do is flatten one end of the straw. The easiest
way to do this is to use your teeth. Put the end of the straw in your mouth
and use your back teeth to bite it a few times. You want to flatten at least
an inch at the end of the straw.
Once you get it nice and flat, then we want to trim it with the scissors to
shape it into a point. Snip off a triangular shaped piece from each side of
the straw. You want the point to be long and thin. Bite the pointed end a
couple more times, to be sure it is nice and flat.
Now put the pointed end into your mouth and blow through it. You want to
blow fairly hard. You should hear a sound like a duck. If you don't, then try
biting the end a couple more times and blow a little harder. If that does
not work, then trim the point to make it longer and thinner.
Now that you have a way to make lots of annoying sounds, how about some
science? Blow the quacker again and notice what you feel. When it makes the
sound, you can feel the straw vibrating. Anything that makes a sound is
vibrating, but usually you don't get to feel these vibrations.
What makes the vibrations? When you blow through the straw, the air inside
the straw is moving faster than the air outside. According to Bernoulli's
Principle, fast moving air exerts less pressure than slow moving air. That
means that when you blow, the higher pressure on the outside pushes the
pointed part of the straw closed. That stops the flow of air and the straw
opens up again. As soon as it opens, the air starts moving and the pressure
outside the straw forces it closed again. This rapid opening and closing is
what causes the vibration. That is why you have to blow hard. You want the
air to move fast enough to make the difference in pressure strong enough to
push the straw closed. You want the end to be flat so that it does not have
to close very far. You cut the straw into a point to make it easy for it to
bend open and closed.
All in all, a very simple experiment with a lot of science in it. And you
get to make funny sounds too.
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com
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