First you need to know some facts about air andwater:1. Water evaporates and is called water vaporwhich behaves like all other gases.2. When any gas expands rapidly it cools; whencompressed rapidly it heats up.3. Cool air can’t hold as much water vapor in itas warm air can.4. In the center of any cloud droplet (a tiny dropof water too small to fall to the ground) there isa tiny piece of matter…dust, salt etc..5. When water vapor condenses to liquid it musthave 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 valvestem get warm or cool…..what happens when youlet air out rapidly out?C. Why does dew collect on the outside of a glassof ice?D. Why do clouds form primarily on the windward sides of mountains? Why is there morerain 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 pumpingair into the bottle. There is a

check valve here that onlyallows air to go one way

First, pump air intothe bottle raising thepressure.

After a few seconds the temp of the air is thesame as the room

Open the hose to the air willrush out and the pressurewill 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 bottlewill help…..why?

Adding the smoke fromproduced when blowingout a match will help. Why?

Lets try again….this time with lots of very tinysmoke particles in the bottle and a lot more watervapor in the bottle.

A cloud is born!!!

Now you can explain what causes the cloud to form….next is a movieshowing the Making of a Cloud…

Can you explain, now, what makesthe cloud quickly go away?

Click on slide to start movie; here to stop

ocean

mountain

Garden GrovePalm Springs

Warm moist air

less pressure

more pressurerain

dry