Physics › Section T · Special relativity › Topic T.4
Relativistic addition of velocities
Add two speeds close to that of light the old way and you get more than light speed, which nature never allows. Relativity replaces simple addition with a formula that agrees with it at everyday speeds but never exceeds c.
In this topic
- When simple addition breaks
- Setting up the frames
- The relativistic rule
- Light and the speed limit
- Worked example: launching a probe
- Worked example: two ships meeting
- Why everyday speeds add simply
- The relativistic Doppler effect
- Worked example: a receding galaxy
- Common mistakes to avoid
- Key takeaways
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