Amplitude and wavelength
Two measurements come straight off the graphs: how far the particles move, and how far it is from one crest to the next.
Amplitude
The greatest displacement a particle taking part in the wave makes from its rest position is called the amplitude of the wave.
Wavelength (λ)
The distance from one particle taking part in the wave to the nearest other particle in exactly the same state of motion is called the wavelength (λ).
Crest to crest
A particle at a crest has reached its greatest displacement. The particle at the next crest is in exactly the same state. So the distance between two neighbouring crests is one wavelength — and so is the distance between two neighbouring troughs.
| x (m) | 1 | 3 | 5 | 7 | 9 |
|---|---|---|---|---|---|
| y (cm) | 2 | -2 | 2 | -2 | 2 |
On this graph the crests at 1 m and 5 m are one wavelength apart: λ = 4 m. The amplitude is 2 cm.