Doppler Effect Frequency Shift Calculator
Calculate classical acoustic and electromagnetic Doppler effect frequency shifts (f'), relative velocity, Mach numbers, and musical pitch semitone changes.
Calculated Results
Frequently Asked Questions
What is the classical Doppler effect formula?
When a wave source moves relative to an observer: f' = f0 × [c / (c ∓ vs)], where c is wave speed, vs is source velocity (subtract vs if approaching, add vs if receding). Wavelength compresses as the source approaches and stretches as it moves away.
Why does an approaching siren suddenly drop in pitch as it passes?
As a police car approaches, sound waves bunch together, elevating pitch. The instant it passes, the waves stretch out behind the vehicle, creating an abrupt audible downward frequency drop.
How do police radar guns use the Doppler effect?
Police Doppler radar bounces microwave radio pulses off a moving vehicle. The reflected frequency returns shifted by Δf = 2 × f0 × (v / c); measuring this microscopic frequency shift calculates vehicle road speed instantaneously.
What is relativistic Doppler shift in astronomy?
For distant stars and galaxies moving at significant fractions of light speed, astronomers observe 'redshift' (receding galaxies, stretching light toward red wavelengths) and 'blueshift' (approaching objects), which proved the expansion of the universe.