Physics
Constructive vs Destructive Interference
Quick fact
Noise-canceling headphones use destructive interference: a speaker produces sound waves exactly out of phase with ambient noise, effectively canceling it out for the listener.
Why this is interesting
Have you ever noticed how ripples in a pond can sometimes grow into a bigger wave, and other times disappear? That's interference—and it's the same principle that makes noise-canceling headphones work.