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The Air Pump
exhibit demonstrates how the patterns of air pressure change when
a piston pump is cranked manually and forces air into a tank. As
the crank is turned, the pressure is observed on a computer screen.
The crank is turned until the screen stops rising. Then a STEP BY
STEP lever is pressed to release air from the tank bit by bit, and
again the pressure patterns are observed. Each turn of the crank
pumps air into the air tank. But as the air pressure in the tank
increases, less air flows into the tank with each pump. On the screen,
the curve rises with increasing pressure but begins to flatten out
as the pressure reaches the maximum. The same is true when you release
the air with the STEP BY STEP lever. With each push of the lever,
there is less air pressure in the tank, so less air flows out. On
the screen, the steps showing decreasing pressure get smaller and
smaller. The flow of air in and out of the tank is an example of
a mathematical pattern called
exponential decrease
. The amount
of air that enters or leaves the tank is a percentage of the air
that's in the tank. Anything that repeatedly decreases by a fixed
percentage is experiencing exponential decrease.
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