Los Gatos High School
How to Make a Cloud in a Jar
At this time of year, we get rain and - if we are really lucky and it gets very cold and the conditions are right - we get snow. Snow is made up of tiny ice crystals, and ice is frozen water. We see water in three forms all the time: solid ice, liquid water like we get from the faucet and drink, and water vapor gas. Here is a picture of water in all of those forms:
This picture also shows everything you will need to do this experiment: ice, water and something to heat it in, a glass jar with a lid (or a bowl), and a match.
It's hard to believe there is water in the air since we can not see it. Here is an experiment you can do to prove that there is a little water in the air.
Fill a jar with ice and water and put its lid on. Wipe it so you know it is dry. Let it sit for several minutes. When you touch the glass, it will feel a little wet. How did the water get there? It couldn't come out of the lid or through the glass.
The trick is water can change between a liquid, solid (ice) and gas. You've seen that when a a puddle dries up in the warm sun and the water turns into a gas, or when a pot of water boils. When water changes like this from a liquid to a gas, we call this evaporation. When the water gas gets cold, it can change back into a liquid, and we call that condensation.
There isn't much water in the air here now, but the little water that is in the air is turning from a gas back to liquid water when it touches the very cold glass. That's why we need to use coasters and why cold bottles and cans may look like they are sweating. It's actually water vapor in the air condensing into liquid water. You can see the thin film of water that formed outside the jar when I tried it.
The water in the air condenses and turns into water when it gets cold. We know that. Why do we have clouds? What are they?
Let's try to make a cloud. Rinse and dry your glass jar. Fill it with about an inch of water that is very hot - almost boiling (you will need a grown up for this part - boiling water is dangerous). Put the lid on the jar and see what happens. What do you see? Did you get a cloud?
Here is what happened when I tried. I added blue food coloring to my water so it would be easier to see and look cool:
I got droplets on the sides of the glass jar and a little steam inside my jar, but not really a cloud. Why do you think I got drops on the sides, and not rain?
The side of the jar is touching the colder room air, so that is where the hot water vapor condensed. Instead of making rain, it just stuck to or ran down the sides of the jar.
There are two tricks to making a cloud:
1) We need really cold air. We will use some more ice. You can place a small bowl on top of the jar, or a sieve, or even turn the lid upside down and fill it with ice. Anything that will make hold the ice on top of the jar and make the air at the top of the air really cold.
2) Tiny particles in the air from dust or smoke act like tape. The water droplets stick to them, and they cluster together to make a cloud. To really make a good cloud, we need some particles in our jar.
Try the experiment again. Dump out the old water, get your ice holder ready and full of ice, and get a match. Put new very hot water in the jar, light the match and hold in the the jar for 1 second and drop it in the water, cover the top of the jar tightly wand top it with ice. Look closely to see what happens!
This was my set up:
Here is what I saw:
Can you see the air swirling around as the cold and warm air meet? We get storms when cold air and warm air collide, just like this.
After a couple of minutes, my jar seemed to fill with smoke, but the match wasn't burning. This is the cloud. Have you ever felt a cloud? How do you think it will feel? Open the jar and feel the cloud as it comes out. Is it cold or warm? Smoky or wet? If it reminds you of fog, that is because fog is a kind of a cloud. If you have walked in fog, you have walked inside of a cloud!
Presented by: Elizabeth Greer, Lakeside Science & Art Teacher