January 14, 2011

Cloud in a Glass

We found a simple weather experiment online and tried it at home this morning. The idea is to make water condense in a glass to simulate cloud formation. You fill a glass about a quarter full with warm water and place an ice cold metal dish on top. The water vapor in the warm moist air trapped in the glass is supposed to condense as it cools near the cold dish and form a cloud.

Our first attempt didn't work. I think the problem was a combination of the water not being warm enough and a gap where the rim of the glass and the bottom of the bowl met.

First try. No cloud, just some condensation on the bottom of the bowl.
So we tried again. This time we heated the water more and put it in a different cup, one that we hoped wouldn't have a gap. We heated the water too much because the water was steaming even before putting the cold dish on top. The glass immediately fogged up with condensation and we couldn't see whether a cloud was forming inside or not. Steam escaped through the gap again.

Second try. The water was so hot that it immediately fogged up the glass.
So we tried a third time. We let the water cool a little and covered the glass with plastic wrap so no water vapor could escape. We put the ice on the wrap and watched the condensation happen. Again, no visible cloud inside the glass.

Third try. We definitely saw condensation, but no cloud.
 This experiment turned out to be a good one for the kids to learn that whatever the expected outcome, good scientists don't fudge their results. Instead, they learn from what they observe and think about how to structure the experiment better next time. We did observe condensation when hot moist air met cooler air, and the kids could visualize how clouds would form. Here are their write-ups.


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