Re: HOW CAN I EXPLAIN AND SHOW EVAPORATION IN SCHOOL?

Dear Kristina,

To explain evaporation of water molecules, you can use an Olympic swimmer analogy: Think of the swimmers as water molecules, where some swimmers have more "energy" than others and move faster. So the fastest (most energetic) swimmers get to leave (evaporate from) the pool first. The rest of the swimmers come out in order of how energetic they are, the slowest being the last to leave the pool. This explains why we are cold when we step out of the tub after a bath or shower: the warmer (more energetic) water molecules on your skin jump off or evaporate first, leaving the colder (less energetic) molecules behind...

To show the evaporation of water, the easiest thing to use is paint since inks tend to dry too quickly. One nice property of water is its conductivity. So water-based paints (when wet) will conduct electricity; once it dries, the paint no longer has enough water to allow electricity to flow through it. You can use conductivity to show evaporation and even how fast it evaporates. There are two ways to do that: the boring, and the fun way. Either way does not cost a lot of money to do.

The boring way: Get a voltmeter (measures how conductive something is). Place both wires into a small blob of paint and turn it on. The dial will read a high number (lots of conductivity because there's lots of water). As the water evaporates and the paint dries, the reading begins to drop until it gets to zero (completely dry).

The fun way: Go to your local RadioShack (electronics store) and get four things: wire, a battery, a battery holder and a tiny lightbulb. Don't worry, the people behind the counter will be able to help out if you tell them what you are trying to do. Connect the battery to the lightbulb with the wires. I've done this already and don't worry, it's safe. Cut one of the wires in half and stick both ends into a little paint puddle and watch the bulb light up! As the puddle dries up, the lightbulb gets dimmer and dimmer...Once the paint completely dries and all the water has evaporated, there is no water left to conduct electricity through the paint and the lightbulb goes dark.