Lectures on Physics has been derived from Benjamin Crowell's Light and Matter series of free introductory textbooks on physics. See the editorial for more information....

Doppler shift of the light emitted by a race car

Question: What is the percent shift in the wavelength of the light waves emitted by a race car's headlights?

Solution: Looking up the speed of light in the front of the book, v=3.0x108 m/s, we find

i.e. the percentage shift is only 0.000017%.

The second example shows that under ordinary earthbound circumstances, Doppler shifts of light are negligible because ordinary things go so much slower than the speed of light. It's a different story, however, when it comes to stars and galaxies, and this leads us to a story that has profound implications for our understanding of the origin of the universe.

Last Update: 2009-06-21