Cloud in a Jar

On a recent foggy walk to school, my 3 year-old, Q,  asked what made fog. Making a cloud in a jar was the perfect opportunity to show him just how clouds and fog (which is just low lying clouds) are formed.  With virtually no prep and no cost, this super cool demonstration will have you playing Zeus, the god of weather, all afternoon.

These ideas are the perfect addition to our 30 Science Experiments in our shop that kids will love!

Getting Ready

For this demonstration I first grabbed a few things we already had in the house. (No extra trips to the store required!)

• glass jar with lid or a glass cup with a small plate
• matches or hairspray
• hot water
• ice

Making the Cloud

This demo couldn’t be easier and really could be done by your kiddo from start to finish.  To get started, we added a couple inches of warm-hot water to our jar. (We originally followed the directions we’d found on other sites suggesting boiling water but that created so much condensation on the inside of the jar that we couldn’t actually see the cloud forming. Hot tap water worked much better.)

Next, we took the lid to the jar, turned it upside down, and filled it with ice.

The final step was to add condensation nuclei or a seed- some tiny particles of dust, salt, pollution, or smoke that the water vapor can condense on in the air.  We used the smoke from matches as our seed but for a kid-friendly version, you could  use a spritz of aerosol hairspray instead.

We found it worked best to blow the match out inside the jar so most of the smoke would become trapped inside. So I lit the match, placed it inside the jar and Q blew out the match before he quickly placed the lid with ice on top of the jar.  (If you are using a glass cup, use a plate with ice to cover your cup.)

You can see at first the glass is clear because no condensation has formed yet.  Within seconds, however, faint swirls of cloud form.

After a minute or two comes the best part of the whole process: letting out the cloud.

It’s hard to capture how cool we both thought this was.  No joke, we repeated this demonstration over a dozen times until we ran out of matches.  So simple, but so awesome!

The Science Behind It

For clouds to form they need 3 things; water, cool air, and condensation nuclei.

Water vapor evaporates from the surface water.  As it rises, the air cools.  The cooler air higher in the atmosphere cannot hold as much water vapor as the warmer air near the surface of the earth.

Some of the water vapor wants to condense, but in order to change from a gas to a liquid, water needs a non-gaseous surface.  Cloud condensation nuclei (CCN) or cloud seeds provide that surface.  CCN’s can be any tiny solid or liquid found in the atmosphere, usually salt from the ocean, dust, or pollution.

In this demonstration you added water vapor to the jar by using warm water.  The smoke or hairspray acted as the cloud seed.  When you added the ice filled lid on top you cooled the warm air causing it to condense on the the surface of the cloud seed particles, forming a cloud!

More Science Fun for Kids

If you loved making a cloud in a jar, you’ll get a kick out of our 30 Science Experiments (complete with a no prep journal to record results) in our shop!