The Doppler Effect

physics · sound · waves · motion

Sirens get higher. When an ambulance zooms toward you, the sound waves bunch up, making the siren sound higher pitched. As it speeds away, the waves spread out and the pitch drops lower.

Named after a scientist. The Doppler effect was discovered and explained by physicist Christian Doppler in 1842. He figured out that motion changes how we perceive waves.

Works with all waves. This isn't just about sound. Light waves do it too, which is how astronomers can tell if distant stars are moving toward us or away from us.

Perfect at the moment. Right when a moving vehicle passes directly by you, the pitch is the same as it really is, because the motion isn't squishing or stretching the waves toward your ear anymore.