When it’s really cold outside–to the tune of -40 degrees (Fahrenheit or Celsius)–physics can get a little crazy. In this photo, boiling-hot water from a thermos turns into an instant snowstorm when tossed. How is this possible? It turns out there are a combination of factors that affect this. Firstly, the rate of heat transfer between two objects depends on the magnitude of the temperature difference between them. The bigger the difference in temperature, the faster the hot object cools. Of course, as the hot object cools down, the temperature difference between it and its surroundings is smaller and the rate of heat transfer decreases.
The second important factor here is that the water is being tossed. When you throw water, it breaks into droplets, and droplets have a large surface area compared to their volume. As it turns out, the rate of heat transfer also depends on surface area. By breaking the hot water into smaller droplets, you increase the surface area exposed to the cold air, allowing the hot water to freeze faster. (Image credit: M. Davies et al.; via Gizmodo)
Also: Since there are a few events scheduled around the country over the next couple months, I’ve added an events page where you can find details for those appearances. And as always, if you’re interested in scheduling a talk or event, feel free to contact me directly.