Hair straightener, by Amber Kates
That hair isn’t on fire. And the hair straightener isn’t smoking. We’re actually seeing changes in air density caused by the rising heat. Our eyes wouldn’t pick up on any of this. We would just see clear air — in other words, nothing.
Here are a few more images like it — all created by Rochester Institute of Technology students for a science photography assignment, and all showing patterns of air flow.
Candle, by Andrew Kempchinskey / Lighter, Shaun McConnaghy
Burning hand sanitizer, by Nick Neumann / Marshmallow, by Benjamin Davis
These last two visualize flow that isn’t caused by heat:
Golf ball, by Joseph DeMartino / Soda, by Jena Pedersen
Here’s how these images were made:
The technique has a fancy, partly-German name: Schlieren Flow Visualization. It can be used reveal any change in air density. Engineers use it to test the aerodynamics of different vehicles, like this YT-1300 light freighter:
Looking at these videos got me thinking: Sound is just a moving compression wave. It creates areas of more dense air and less dense air. Could I use this technique to SEE sound?
Stay tuned for the answer!