Atmospheric Pressure
Scientists called meteorologists
use a special instrument called a
barometer to measure the
pressure of the atmosphere. What
exactly is it that they are
measuring? What is pressure?
To understand pressure, consider
a sponge. When left alone, a
sponge stretches out to its full
size. As you squeeze down on the
sponge, what happens? How
small can you make it? Can you hide the sponge entirely within your
hand? When the sponge is squished up as tightly as you can make
it, how does it feel? The sponge should feel hard and tight. Now, as
you let go of the sponge and it once again takes its original size and
shape, how does it feel? In this state, it should feel soft again.
The atmosphere is similar to a sponge in that it can be compressed,
or squished up. The weight of the air above compresses the air
below tighter and tighter. The lower we travel down into the
atmosphere, the more weight there is above, and so the tighter the
air is squished or compacted. The higher we travel into the
atmosphere, the less air there is above and so the less weight there
is pushing down, and as a result, the less squished up, or the less
compact the air.
Half of the air making up our atmosphere is squished down into the
first three layers, and 90% of the atmosphere is squished into the
first 10 miles (16km). Above this altitude the air is so thin that the
pressure is even less than that of the best vacuums on the surface
of the Earth.
Summarize what you have read below in 3 to 5 sentences.