Demonstration of Standing Waves

Two waves, indicated in red and blue, have equal frequency and wavelength, but the red wave is moving to the right, and the blue wave is moving to the left. The white wave is obtained by adding the red and blue together.

Only the combination wave is shown below. Note that some points don't move at all.

This is an example of a standing longitudinal wave. Notice that some "molecules" don't move as much as others.

You may compare these with travelling waves.