Thursday, October 11, 2018

Homeschool Science Meteorology Unit: Condensation Demonstrations

Temperature and water are the keys to weather, and modeling how they work on the small scale allows you to more easily use your imagination to see them happening up large in the sky.

Here's where we modeled air flow.
Here's where we modeled how temperature affects the flow of both air and water.

And here's where we model how temperature causes water to change states!

If you've got younger kids, I'd spend quite a while on the water cycle with them first (I really, really, REALLY like this water cycle dice game!), but with my older kiddos, we just briefly reviewed it as a reminder of the big picture, then focused on our models and how they scale up.

First up is a demonstration of condensation that models the dew point. The dew point is simply the temperature at which water vapor condenses into liquid water, and it's simple to model just by forcing a liquid to drop to a temperature cold enough to cause condensation. You need a metal can, crushed ice, salt (optional) to lower the water's freezing point, and a thermometer to measure the liquid's temperature.

This textbook is Air Environment, Module 3 of the Civil Air Patrol's Aerospace Dimensions curriculum. With supplementation, it made the perfect spine for a six-week meteorology study.
Fill the can halfway with very cold water, then add crushed ice by the spoonful, stirring, observing, and measuring continually. I did not want the children to use their thermometers as stirring sticks, but it turned out to be impossible to stop them, grr:

When the outside of the can is cold enough, water vapor from the room will begin to condense. You want to notice the exact moment that condensation begins to appear on the outside of the can, then measure the water temperature.

Will also wanted to measure her body temperature. Goodness knows where these thermometers have been, much less the fact that they're currently actively involved in a science experiment. And yet, my little mad scientists are difficult to subdue:

I made a point later in the day to show them the "Can You Lick the Science?" memes...

We tried a couple of other condensation demonstrations that are meant to model rainfall. For the first one, fill a clear jar maybe a third full of very hot water--

--then rubber band a paper towel to the top and pile ice cubes on top of the paper towel:

You remember from our convection current lessons that hot air containing water vapor will rise. It will meet the cold air at the top of the jar, at which point the water will condense on the inside of the jar.

That demonstration ran okay, but as the kids were running it, I realized that a solar still would make an ever better  demonstration, and so we built one! Sort of...

This is the same as the previous demonstration, except that I had the kids put a layer of plastic over the top of the jar:

Now, when they added hot water and cold ice, none of the hot water vapor could escape, and it condensed on the plastic, resulting in genuine raindrops!

You wouldn't have ice, obviously, on a solar still, but would rely on the sun to warm the water enough to cause it to rise and condense. Make sure that the middle of the plastic is the lowest point so that all the raindrops fall from there, and put another container below that spot to collect the water, and drop by drop, you'll have dirt-free water to drink.

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