The first 3 minutes of this video show how to do the activity. The final 4 minutes are highlights of my students doing the activity. CLICK HERE to read the guidelines, and gain access to a PowerPoint and a student handout.
Hidden heat . . .
Most people understand that storms transport moisture from the oceans to continents. But, another important aspect of storms, often over-looked and not well-understood, is that they transport heat as well. It's easy to convince students that water molecules in those snow-flakes falling outside evaporated from the ocean a few days ago, however convincing them that storms transport heat is a tougher sell. Actually, the two (moisture and heat) are closely related. As water molecules evaporate from the ocean, they absorb heat in order to make the phase change. Then, as that vapor changes back into liquid droplets in a hurricane or ice crystals in a winter storm, this heat is released into the surrounding air. Called latent heat, this is the "energy" that fuels hurricanes and the warmth of Chinook winds, and it plays an important role in microbursts and other interesting things that happen in the real world.
Seeing is believing . . .
The best thing about this activity is that students actually get to watch the temperature of water rise dramatically as water freezes right before their eyes! They will use a beaker of salty slush to supercool (-5) two test tubes of water. Then they will "trigger" the freezing. As the water molecules change from liquid to ice (within seconds), they release latent heat. This causes the temperature of of thermometers in the water to rise (also within seconds). The show doesn't last long, but it is pretty cool to see the surprise on students' faces as they watch it happen.
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