The Doppler Effect
The apparent change in frequency of a wave due to the relative motion between a source and an observer.
Discovered By
Christian Doppler (1842)
Core Idea
Approaching sources appear higher in frequency while receding sources appear lower in frequency.
Applications
Radar Guns, Medical Ultrasound, Astronomy, Weather Monitoring and Satellite Tracking.
What Is The Doppler Effect?
Imagine an ambulance rushing toward you. The siren sounds noticeably higher in pitch as it approaches. Once it passes, the pitch suddenly drops. This familiar phenomenon is called the Doppler Effect.
The effect occurs because motion changes how closely packed the wavefronts become. When the source moves toward an observer, wavefronts compress, increasing the observed frequency. When the source moves away, wavefronts stretch apart, decreasing the observed frequency.
Interactive Doppler Simulation
Move the source and observe how the wavefronts compress in front and spread behind. The displayed frequencies update in real time.
Real World Applications
🚔 Radar Speed Guns
Police radar measures vehicle speed using Doppler shifts of reflected radio waves.
🫀 Medical Ultrasound
Blood flow velocity is determined using Doppler ultrasound.
🌌 Astronomy
Redshift and blueshift reveal whether stars and galaxies are moving away from or toward Earth.
🌦 Weather Radar
Doppler radar tracks wind speed and storm movement.
Redshift and Blueshift
Light waves also exhibit the Doppler Effect. A star moving toward Earth appears shifted toward shorter wavelengths (blue). A star moving away appears shifted toward longer wavelengths (red).
Moving Toward Observer
Moving Away From Observer