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Both calculators run independently — change the inputs on either side to compare results.

Relativistic Doppler Shift Calculator

Calculates the observed frequency of light or sound when source and observer move at relativistic speeds. Use it when relative velocity is a significant fraction of the speed of light.

Rest Frequency (Hz)

Relative Velocity (m/s)

Direction

Fill in the required fields to see your result.

Relativity

Relativistic Velocity Addition Calculator

Adds two velocities correctly under special relativity so the result never exceeds the speed of light. Essential when objects move at a significant fraction of c.

First Velocity (m/s)

Second Velocity (m/s)

Fill in the required fields to see your result.

Key differences

	Relativistic Doppler Shift Calculator	Relativistic Velocity Addition Calculator
Category	Relativity	Relativity
Inputs required	3	2
Result	Observed Frequency (Hz)	Combined Velocity (m/s)
What it does	Calculates the observed frequency of light or sound when source and observer move at relativistic speeds. Use it when relative velocity is a significant fraction of the speed of light.	Adds two velocities correctly under special relativity so the result never exceeds the speed of light. Essential when objects move at a significant fraction of c.