Saturday June 01, 2013
Blowing on a hot cup of tea to cool it - works!
This is a movie taken with a thermal camera, so the hottest areas show up brightest. When a hot piece of iron cools, it glows yellow, then orange, then red, then finally goes dark - at least to our eyes. It’s still glowing, just at lower-energy infrared light. In exactly the same way that hot iron glows, this hot cup of tea, cooler than the iron, is glowing in infrared light. (We glow in infrared light, too) The thermal camera I’ve been using in the lab works just like a regular camera, except it’s sensitive to infrared light instead of visible.
You can see that blowing on a hot cup of tea works, but the effect is temporary, since hotter liquid quickly swirls up from the bottom of the teacup to replace the tea your breath cooled. This video is sped up slightly, since I had to reduce the number of frames to get it to fit on Tumblr.