Rhea -
Sure. You probably already know that air pressure
goes down at high altitudes. That's because it's gravity that's holding
the air near the Earth. You can think of it this way - the pressure at
some height has to be enough to support the weight of all the stuff
above it. The higher you go, the less stuff is above you, so the lower
the pressure.It's a nuisance to travel to some other altitude to check
that. Since water is a lot denser than air, in water the pressure
changes a lot even for small height differences. Here's how you can use
water to see the way gravity affects pressure.
Get an empty
2-liter soda bottle and poke several small holes in it going up the
side of the bottle. Plug all of the holes up (you may be able to do
this with the needles that you used to make the holes). Fill the bottle
all the way up and pull the plugs out. The water will shoot out of the
holes because of the pressure of the water pushing out. The higher the
pressure of the water, the farther the water will shoot. What you will
probably see is that the water coming out of the bottom holes will
shoot farther than the water from the top holes. The pressure of the
water is higher as you go deeper into the soda bottle. Its the same
reason you feel the pressure on your body (in particular your ears)
rise as you dive to the bottom of a pool.
This is also the
reason that human divers can't go below a certain depth in the ocean.
For humans, pressures of more than 20-80 atm can cause problems, which
is equivalent to about 650-2600 meters underwater. Although humans
generally don't try to dive this deep, some seals have been known to
dive more than 650 meters below sea-level, so that they have to have
special adaptations to let them survive at high pressures. For more
info on exactly how to calculate all these numbers, check out the
answer to the question .
-Tamara
(published on 10/22/2007)
