Progressive waves
Progressive wave: a travelling disturbance that transfers energy while the material through which it travels has no overall motion with the wave.
In a mechanical progressive wave, particles of the medium oscillate about their equilibrium positions while the disturbance travels through the medium.
- Displacement, : the vector distance of a particle from its equilibrium position.
- Amplitude, : the greatest magnitude of the displacement from equilibrium.
- Wavelength, : the separation between successive points that are at the same stage of the wave cycle.
| Quantity | Meaning | Unit |
|---|---|---|
| Displacement, | Position relative to equilibrium, including its direction. | m |
| Amplitude, | Maximum magnitude of displacement from equilibrium. | m |
| Wavelength, | Distance between successive points in phase. | m |
| Period, | Time taken for one complete oscillation. | s |
| Frequency, | Number of complete oscillations occurring each second. | Hz |
| Wave speed, | Distance travelled by the wave per unit time. | m s |
| Phase | The position of a point within an oscillation cycle. | rad, degrees or fraction of a cycle |
| Phase difference | How far one oscillation leads or lags another within the cycle. | rad, degrees or fraction of a cycle |
Exam Tip: Draw amplitude from the equilibrium line to a crest or trough. Draw wavelength between equivalent successive points, such as one crest and the next crest.