Blow across the top of a glass bottle, and you’ll get a whistle-like sound. Put some liquid in there and the pitch of the sound changes. Our vocal tracts are basically the same thing: a tube with a hole at the end. But as Joe Hanson shows in this Be Smart video, our ability to change the shape and resonance of our vocal tract by moving our tongues and lips enables us to make a wide range of vowel sounds. Enjoy this dive into the world of linguistic physics! (Video and image credit: Be Smart)