Chalk this up under "Blogs You Ought to be Following". The Tumblr Fuck Yeah Fluid Dynamics is a great place to find succinct, clear explanations of the forces that make things flow. In particular, they're fantastic at posting explanations behind things you see in YouTube videos, both viral and obscure.
The video above — in which a nice Siberian guy tosses boiling water off his balcony and creates a cloud of snow — has been making the rounds recently. Here's how Fuck Yeah Fluid Dynamics explains it:
Several effects are going on here. The first thing to understand is how heat is transferred between objects or fluids of differing temperatures. The rate at which heat is transferred depends on the temperature difference between the air and the water; the larger that temperature difference is the faster heat is transferred. However, as that temperature difference decreases, so does the rate of heat transfer. So even though hot water will initially lose heat very quickly to its surroundings, water that is initially cold will still reach equilibrium with the cold air faster. Therefore, all things being equal, hot water does not freeze faster than cold water, as one might suspect from the video.
The key to the hot water’s fast-freeze here is not just the large temperature difference, though. It’s the fact that the water is being tossed ...