Watch how wave frequency changes when a source moves relative to an observer. Wavefronts compress ahead of motion (higher frequency) and stretch behind (lower frequency).
The Doppler effect describes the change in observed wave frequency due to relative motion between source and observer.
Frequency Shift:
• Observer ahead of source: f' = f₀ · c/(c - v) (higher frequency)
• Observer behind source: f' = f₀ · c/(c + v) (lower frequency)
Where f₀ is emitted frequency, v is source velocity, c is wave speed
Mach Number: M = v/c
• M < 1: Subsonic (wavefronts ahead are compressed)
• M = 1: Sonic (wavefronts pile up, forming shock wave)
• M > 1: Supersonic (Mach cone forms with angle α = arcsin(1/M))
Applications: Radar speed detection, astronomy (redshift/blueshift), medical ultrasound, weather forecasting (Doppler radar).