A float bobs on a swimming lake, and a logger records the float's height above and below calm level, moment by moment. The printout shows a wave shape, but its horizontal axis reads time in s, not position.
The float is the thing measured: one point of the lake, bobbing over its own spot. Drawn out, its record is a graph that follows that one point through time, and its two reads are the amplitude again, and a time instead of a length.
Watch the float first: it rises, falls, and rises again, always over the same patch of water. Its height above and below calm level is the thing being measured.
The logger writes that height down moment by moment: one point of the lake, followed through time.
Drawn with axes, the record becomes a displacement-time graph: time, in s, runs across; the float's displacement, in cm, runs up.
The amplitude reads off the vertical axis, exactly as before: the displacement at a peak, measured from zero.
Read the period from one peak to the next peak; trough to next trough gives the same period at the other landmark.
Same curve shape as the snapshot graph, different horizontal axis, different repeat quantity: there a wavelength, here a period.
A displacement-time graph of a buoy shows peaks at displacement 3 cm, one peak at 1 s and the next at 6 s. Read the amplitude and the period.
Amplitude: the peak sits at 3 cm on the displacement axis, so the amplitude is 3 cm.
Period: successive peaks sit at 1 s and 6 s.
6 - 1 = 5
Amplitude 3 cm; period T = 5 s.
The graph follows one cork on a pond through time. Enter the wave's amplitude in cm.
The graph follows one buoy through time. Successive peaks sit at the times marked by the read guides. Enter the wave's period in s.
Cosmo reads a displacement-time graph of one float and says: 'Successive peaks on this graph sit 0.5 s apart, so one complete wave takes 0.5 s to pass the float.' Is Cosmo correct?
The graph follows one mooring float through time. Successive peaks sit at the times marked by the read guides. Enter the wave's period in s.
The graph follows one patch of floating foam through time. Enter the wave's amplitude in cm.
Which procedure gives a wave's period from a displacement-time graph of one point?