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Recipe for Snow: Just boil water

Every fall and winter since I moved to California I complain to one friend or family member (probably more) about how much I miss the seasons of Northeastern Pennsylvania. Every visit home reminds me of how beautiful the tress are, especially when they shed their brilliant leaves in the fall. I, having always been a cold weather person, absolutely love the snow. But this week while all my friends and family back home were hiding from the subzero temperature cause by the polar vortex (which is quite possibly the most bad ass sci-fi sounding name an extreme weather event has ever had), I was walking my dog in just a t-shirt. Hmmm, guess things aren’t so bad after all.

Since I have so many friends currently suffering the terribleness of multi-day school closures (the horror!) I have been kept very much up to date on the situation thanks to social media. One of the coolest and I think most interesting things I’ve seen from all this are the videos of people spraying boiling hot water into the air and having it instantly turn into snow. Even as a scientist this intuitively made no sense to me. OK yes, I get it’s really cold out, but why would boiling water be turning to snow? Why not cold water? Or even lukewarm water?

Well it turns out that this is a physics thing (no wonder it makes no intuitive sense to me). It is called the Mpemba effect which describes the phenomenon where hot water freezes faster than cold water. The theory goes like this: hydrogen bonds (the H in H2O) are what hold water molecules together. They’re why if you out a drop of water on a table it stays round instead of spreading out, we call this surface tension. Well, it turns out that when you heat water up, these bonds stretch which causes the molecules to give up energy. The funny thing is, giving up energy is what happens during cooling also. So boiling water is actually primed and ready for freezing.

If this still seems a little weird to you, you’re not alone. But even if you can’t believe the science, you can’t argue with the proof.

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