Interactive simulation of the Doppler effect. Watch wavefronts compress ahead of a moving source and stretch behind it. Cross the speed of sound to see a Mach cone form.
A moving source emits wavefronts at equal intervals, but because the source moves between emissions, the fronts bunch up ahead (higher frequency) and spread out behind (lower frequency). At Mach 1, fronts pile into a shock wave â the sonic boom.
Adjust source speed and wave frequency. Add a second stationary observer to compare received frequencies. Push the speed past Mach 1 to see the Mach cone angle decrease as speed increases.
The Doppler effect applies to all waves. Police radar uses it for speed measurement, astronomers use redshift to measure galaxy recession speeds, and medical ultrasound uses it to measure blood flow velocity.