Friday, December 13, 2013

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!

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