Displacement against distance
Now freeze the wave at one instant and look along it: the displacement of every particle, against its distance from the source.
| x (m) | 1 | 3 | 5 | 7 | 9 |
|---|---|---|---|---|---|
| y (cm) | 2 | -2 | 2 | -2 | 2 |
After Figure 4.11 — the displacement of each particle at one instant, against its distance from the source. Here the wavelength is 4 m and the amplitude 2 cm.
For a transverse wave, such as a wave along a rope, this graph is simply the shape of the wave you would see at that instant. A longitudinal wave can be described by a graph of the same kind, showing how displacement changes with distance.
Same shape, different axis
This graph and the one on the last page look the same, but they say different things. The last one follows one particle through time; this one photographs every particle at one time. Always read the horizontal axis first.