This Week's Experiment - #286 Air Space
During our shopping, we bought some of the storage bags that you fill with
clothes and then squeeze the air out of so that your clothes take up much
less room in your luggage. They really do work, and since we take LOTS of
stuff, we need all the help we can get. This got me thinking about how much
air space there is in other common substances. To experiment with this, you
will need:
a drinking glass
water
cotton balls
Fill the glass to the top with water, so that the water level is at the very
top of the glass. Now, it would seem that you could not put anything else
into the glass without spilling it.
Pick up a handful of cotton balls. Just by looking at them, you can tell
that there is a lot of air in the spaces between the fibers. Take one of the
cotton balls and squeeze it down as small as you can. Even so, it still
takes up quite a bit of space. How many of them do you think you could put
into the glass of water before the water spills over the side? Lets try and
see what happens.
Don't just cram a handful of them into the glass. Instead, gently place one
of the cotton balls in the water and watch as it soaks up the water and
sinks. Then place another cotton ball in the water. Keep adding them. You
will probably fill the glass with wet cotton long before the water level
rises enough to cause it to run over the edge.
How can this be? Well, a cotton ball is made up of lots of cotton fibers,
all tangled together. Most of the space taken up by the cotton ball is
actually taken up by the air between the fibers. Only a small fraction of
the space is filled with the stands. On top of that, the fibers are mostly
air. Each strand of cotton is actually a long, hollow tube. These tubes are
elongated cells which form on the surface of the cotton seed. When the cells
die, the tough cell wall is left behind, forming the strand of cotton.
Besides filling the spaces between the strands, the water also fills the
hollow inside of the strand. That means that the water level rises only a
tiny fraction with each cotton ball. Since the surface tension of the water
lets it bow upwards quite a bit before it flows over the side, it is very
easy to fill the glass with wet cotton without making a mess. Too bad it
isn't that easy to fit all these clothes into the suitcases.
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com
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