Avalanches and Ice Storms, and making freezing rain on a tile

One of the most interesting things we learned related to avalanches was about the invention of the "avalanche airbag." We did this demonstration with rice to show how lighter and bigger objects "float to the top" of an avalanche (it makes more sense to me to say that the smaller, denser objects sink to the bottom and push the bigger things up, but all our books described it as "floating," so maybe it is). These pictures don't really show what's going on here, but just put a bunch of toys and small objects into a jar full of rice and then shake the jar. The bigger things rise to the top and sit on top of the rice.

It's based on this principle that the avalanche airbags work. Here is one description, and here are a couple videos.

I think I mentioned earlier how I've never understood freezing rain and ice storms? Well, we learned that it's all about the right layers of air. We don't get them much here, but the pictures we've seen are so beautiful! Too bad they cause so much damage. 

Here's a good graphic explanation

Here's another diagram explaining the temperatures necessary for each type of precipitation.

One thing that's present in an ice storm is supercooled rain, which is basically rain that should be ice (it's at a temperature below 32 degrees F) but isn't, either because it has nothing to crystallize onto or because it hasn't had time to freeze. When this supercooled rain hits a cold surface, it freezes instantly onto the surface. We also learned about the types of ice, glaze (clear and smooth) and rime (bumpy and white because of tiny air pockets when it splashed up---it looks more like frost).

This demonstration uses supercooled water to make glaze on a ceramic tile. The instructions we had tried to make supercooled water by using distilled water (fewer dust/mineral particles in the water to provide a "hold" for ice crystallization) in a spray bottle and then removing the bottle from the fridge before it was totally frozen. We followed the instructions, but I'm not sure if our water actually became supercooled, or if it didn't but even water that is nearly supercooled works okay for this. Either way, it worked and it was cool!

To do this activity, you put a ceramic tile (or a smooth rock) into the freezer overnight. Pour distilled water into a spray bottle with the spray lid off. Let it sit, covered with a bit of saran wrap so dust doesn't get in, at room temperature for an hour or two. Then put the covered bottle in the freezer for another couple hours, until the edges are starting to freeze but the middle is still liquid. One of the times we did this, we let the bottle sit in the freezer too long and it froze all the way through. It worked fine to just let it sit on the counter for a little while, till it began to thaw, and then continue with the activity.

Insert the spray top into the liquid water in the bottle, and then remove your cold tile from the freezer and spray the water onto it. It should freeze into ice on the tile almost instantly!

The glaze formed by our "freezing rain"

You can see how we could slide this ice off in a thin, solid sheet. So interesting!

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.