Standing Waves, the Doppler Effect, and Sound

A standing wave, also called a stationary wave, is formed when two waves of the same frequency and amplitude travel in opposite directions and superpose. This commonly happens when a wave reflects back on itself, for example on a string fixed at both ends or in a column of air in a pipe. Unlike a traveling wave, a standing wave does not transfer energy along its length. Instead, it consists of a fixed pattern of points that never move, called nodes, and points that oscillate with maximum amplitude, called antinodes.

Nodes and antinodes alternate along a standing wave and are always separated by one quarter of a wavelength; the distance from one node to the next is half a wavelength. At the nodes the two waves always cancel through destructive interference, while at the antinodes they reinf