## Hands-On-Physics
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## Information |
## - Concepts - |

Waves have speed, and their speed, like the speed of anything, is just the rate of change of position. The speed of a wave is distance a wave-crest travels in a second.

Waves that vibrate regularly (periodic waves) vibrate from maximum (crest) to minimum and back to maximum in a uniform time. This time for this one cycle is called the wave period. During one period (T) a wave crest moves a distance of one wavelength (l). Considering the wave speed during one cycle, d = L and t = T, so:

v = L

Wave timing is sometimes expressed as period (T) which is the time required for one wave-cycle, but it is often expressed as frequency (f) which is the number of cycles per second. The unit for frequency is the Hertz, 1 Hz = 1 cycle/sec. Frequency and period are measurements of the same timing, they are reciprocals.

Wave amplitude describes the shape of the wave. For a water-wave amplitude means height, for a sound wave it means pressure. The model for the amplitude of a periodic wave can be written in terms of time or position.

Figure P1

Fixed position

Figure P2

Fixed time (Snapshot)

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