Doppler Effect Calculator — Frequency Shift

Doppler Effect Guide

What's the key thing to understand about The Doppler Formula?

f_observed = f_source × (v_sound + v_observer) / (v_sound + v_source). Sign conventions: v_observer positive when moving toward source, negative when moving away. v_source positive when moving away from observer, negative when approaching. Simplified for stationary observer and moving source: approaching: f_obs = f_s × v / (v - v_s). Receding: f_obs = f_s × v / (v + v_s). A 440 Hz source moving toward you at 30 m/s (v_sound = 343 m/s): f_obs = 440 × 343 / (343 - 30) = 440 × 1.096 = 482 Hz. Noticeably higher than the source's actual 440 Hz, which is exactly the pitch rise you hear as a vehicle approaches.

What should I know about Everyday Examples?

Ambulance siren: a siren at 700 Hz moving at 50 km/h (13.9 m/s). Approaching: f = 700 × 343/(343-13.9) = 730 Hz. Receding: f = 700 × 343/(343+13.9) = 672 Hz. Total shift heard as it passes = 730-672 = 58 Hz — clearly audible. Racing cars: Formula 1 cars at ~80 m/s. Approaching pitch at ~1.30× source, receding at ~0.81×. The characteristic 'nyeow' sound as a car passes. Supersonic aircraft: when v_source = v_sound, the formula breaks down — a sonic boom is produced (shock wave) rather than a freq

What's the key thing to understand about Doppler in Astronomy — Redshift?

For light, the relativistic Doppler formula applies: z = Δλ/λ = f_source/f_observed - 1. Recession velocity v ≈ z × c for v << c. Hubble's Law: galaxies are receding from us with velocity proportional to distance (v = H₀ × d). The cosmological redshift of distant galaxies provided the first evidence for the Big Bang. Edwin Hubble observed in 1929 that distant galaxies show redshift (light shifted to longer wavelengths) — implying the universe is expanding. The Cosmic Microwave Background is redshifted so dramatically by this same expansion that light originally emitted as visible or ultraviolet radiation is now detected as microwaves.

What's the key thing to understand about Medical Applications of Doppler?

Doppler ultrasound: ultrasound (2-18 MHz) reflects off moving red blood cells. The frequency shift of the reflected wave reveals blood flow speed and direction. Applications: measuring blood flow velocity in arteries and veins. Detecting deep vein thrombosis. Foetal heart monitoring. Echocardiography (heart valve function). Colour Doppler: blood flow toward the probe shown in red, away in blue. Doppler weather radar uses the same principle — the frequency shift of reflected microwave pulses from