Tornadoes, Hurricanes, Convection Currents, and Making a Barometer

You know you can't resist doing the ol' tornado-in-a-bottle activity! We did a couple variations on this. There are millions of resources for it online. We did the two-bottle version (two 2-liter bottles taped together at their mouths) and the jar version (like this), and I will say that I think adding the food coloring makes the tornado harder to see, so I advise against it. If you add glitter or other "debris," you can see things being pulled up by the vacuum in the center, which is kind of interesting.

I always wondered who on earth would buy these tornado tubes when you can just use tape---but our bottles leaked like crazy, so now I get it. If I were doing this repeatedly or with a whole class of students I'd invest in the tubes.

We've looked at water convection currents before, and air convection currents as well, but we did a quick review to precede our discussion on how tornadoes are formed. We also reviewed what we'd learned about vortices from our air vortex cannon. High- and low-pressure weather systems seem like they'd be simple to understand, and they ARE when you think in terms of air density and temperature, but I always have to talk myself very methodically through it to make sure I'm not mixing anything up.

Here's a good article about something that doesn't feel very intuitive---the fact that humid air (air with water in it) is actually lighter than air with less humidity. That means it doesn't push down as hard on the mercury or other fluid in your barometer, so the barometric pressure is lower. Again, this is easier if you actually picture a barometer. Lots of pushing from the air=barometer high, less pressure from the air=barometer low. Making our own barometer helped us keep this straight in our minds. It also helps me to think this: if the air is full of water, the actual air molecules have to be farther apart to fit the water between them, and therefore they exert less pressure on each other. More humidity=lower air pressure.

Here are two kinds of homemade barometers.

General idea for the water barometer here and the air barometer here. Our water barometer froze soon after this picture was taken, so I'd recommend the air one for colder weather! :)

Our friend Jena had the awful, but very interesting, experience of being IN a tornado! She was kind enough to send us some pictures, which were really fascinating to look at. There is something about seeing pictures from a real person instead of news reports---it makes the event seem so much more personal and real.

And here are some tornado pictures we liked from National Geographic.