First you need to know some facts about air and
1. Water evaporates and is called water vapor
which behaves like all other gases.
2. When any gas expands rapidly it cools; when
compressed rapidly it heats up.
3. Cool air can’t hold as much water vapor in it
as warm air can.
4. In the center of any cloud droplet (a tiny drop
of water too small to fall to the ground) there is
a tiny piece of matter…dust, salt etc..
5. When water vapor condenses to liquid it must
have an object or surface to condense on.
A. Does dew form when air heats up or cools off?
B. When you pump air into a tire does the valve
stem get warm or cool…..what happens when you
let air out rapidly out?
C. Why does dew collect on the outside of a glass
of ice?
D. Why do clouds form primarily on the
windward sides of mountains? Why is there more
rain there also?
E. Why is the air more moist on one side of a
mountain than on the other side usually?
Cloud chamber
Bulb for pumping
air into the bottle.
There is a
check valve
here that only
allows air to
go one way
First, pump air into
the bottle raising the
After a few seconds the
temp of the air is the
same as the room
Open the hose to the air will
rush out and the pressure
will suddenly drop inside
1. Does the temp of the air
suddenly drop?
2. Where is the SURFACE
on which water vapor may
condense inside the bottle…
could this make a cloud?
Do you see any clouds?
Adding a little liquid water to the bottle
will help…..why?
Adding the smoke from
produced when blowing
out a match will help.
Lets try again….this time with lots of very tiny
smoke particles in the bottle and a lot more water
vapor in the bottle.
A cloud is born!!!
Now you can explain what causes
the cloud to form….next is a movie
showing the Making of a Cloud…
Can you explain, now, what makes
the cloud quickly go away?
Click on slide to start movie; here to stop
less pressure
more pressure
Palm Springs
Garden Grove
Warm moist air