Sometimes, waves do not seem to move; instead, they just vibrate in place. Unmoving waves can be seen on the surface of a glass of milk kept in a refrigerator, for example. Vibrations from the refrigerator motor create waves on the milk that oscillate up and down but do not seem to move across the surface. These waves are formed by the superposition of two or more identical waves moving in opposite directions. The waves move through each other, with their disturbances adding as they go by. If the two waves have the same amplitude and wavelength, and the oscillations are at fixed locations in space, then they alternate between constructive and destructive interference. The resultant waveform looks like a wave standing in place, and thus, is called a standing wave.
Some other examples of standing waves include those resulting from plucking the strings of a musical instrument, such as guitar strings, and are formed due to reflections of waves from the ends of the string. The points at which the string does not move are called nodes. More generally, nodes are where the wave disturbance is zero in a standing wave. In contrast, the term antinode is used to denote the location of maximum amplitude in standing waves.
This text is adapted from Openstax, College Physics, Section 16:10: Superposition and Interference and Openstax, University Physics Volume 1, Section 16.5: Interference of Waves.
