A rope wave ran in the lab all afternoon: sometimes the whole rope was photographed at one instant, sometimes one marked spot was tracked through time. Dilys finds one unlabeled printout from it, smooth and repeating. Then she spots the horizontal axis label in the corner: seconds. That one word settles what the whole page shows.
One rope wave sat behind both records. Two kinds of wave graph can come from it, sharing one shape, and the repeat distance on the page means a different thing on each. One axis read sorts them.
Start with what was measured. A photograph of the whole rope at one instant records every position at once; a track of one marked spot records one place through time.
Both records rise and fall and repeat, so side by side the two pages look alike.
The difference lives on the horizontal axis. Read which quantity it measures.
A horizontal axis measuring position, in m or cm, makes the graph a displacement-position graph: a snapshot of the whole medium at one instant. Its repeat distance is a wavelength.
A horizontal axis measuring time, in s, makes the graph a displacement-time graph: one point of the medium followed through time. Its repeat distance is a period.
The curve's shape tells you nothing about which: only the axis does.
A wave graph's horizontal axis reads position (m). Is the repeat distance along that axis a wavelength or a period?
Read the horizontal axis: it measures position.
A position-axis repeat is a length along the medium.
The repeat distance is a wavelength.
A second graph's horizontal axis reads time (s). Is its repeat distance a wavelength or a period?
Read the horizontal axis: it measures time.
A time-axis repeat is a time per complete wave.
The repeat distance is a period.
A wave graph's horizontal axis reads time (s). Is the repeat distance along that axis a wavelength or a period?
A wave graph's horizontal axis reads position (m). Is the repeat distance along that axis a wavelength or a period?
A wave graph's horizontal axis reads position (cm). Is the repeat distance along that axis a wavelength or a period?
A wave graph's horizontal axis reads time (s), and its vertical axis reads displacement (mm). Is the repeat distance along the horizontal axis a wavelength or a period?
A logger follows one buoy and plots its displacement against time in s. On the printed graph, is the repeat distance along the horizontal axis a wavelength or a period?
A camera snapshot of a whole rope is plotted as displacement against position in m. On the graph, is the repeat distance along the horizontal axis a wavelength or a period?
The horizontal axis of a wave graph reads time (s). Which quantity is the repeat distance along that axis?
Beata's graph follows the surface height of one fishing float, and its curve repeats every 2 s along the horizontal axis. What is the 2 s?
A graph's horizontal axis label is smudged and unreadable. Anselm wants to know whether the graph's repeat distance is a wavelength or a period. What must he find out?