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When two undulatory movements are propagated through the same region of space, the effect of them both on the medium is called interference.
The interference can give rise to very varied situations, the most important being:
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Constructive interference |
This is produced between waves of equal frequency and wavelength when they are in phase. The result is a wave of equal frequency and wavelength, but with an amplitude equal to the sum of the components. |
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Destructive interference |
This is produced between waves of equal frequency and wavelength if they have a phase difference of half a wave. The result is a wave of equal frequency and wavelength, but with an amplitude equal to the difference between the components. |
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Stationary waves |
These are produced between identical waves travelling in opposite directions. In the resulting wave there are points (antinodes) which vibrate with a maximum amplitude equal to that of the component waves, and points which remain stationary all the time (nodes). | | 
