Beata watches ripples slide past a dock post. Each ridge of water rides a little above the flat level the pond had before, and between the ridges the surface dips a little below it.
Transverse waves have a shape, and the shape has two landmarks. This lesson names them.
The pond's flat, undisturbed level is drawn as a dashed line: the rest position of the surface.
The wave's shape rises above that line and dips below it, over and over.
Crests and troughs alternate along the wave: crest, trough, crest, trough.
A point sitting ON the rest line, between a crest and a trough, is neither: crest and trough name only the highest and lowest points.
These two landmarks come up in every transverse-wave lesson from here on, so check them against the rest line every time.
A snapshot of a rope wave marks point J at the top of a rise, highest above the dashed rest line. What is J?
J sits highest above the rest position.
The highest point above the rest position is a crest.
J is a crest.
The same snapshot marks point K at the bottom of the dip beside J, lowest below the rest line. What is K?
K sits lowest below the rest position.
The lowest point below the rest position is a trough.
K is a trough.
The snapshot of a lake swell marks three points: J, K, and L. Which letter marks a crest?
The snapshot of a rope wave marks three points: M, N, and P. Which letter marks a trough?
Anselm looks at a wave snapshot and says: 'Every crest on this wave sits above the rest line, and every trough sits below it.' Is Anselm correct?
Which statement about the crests of a transverse wave is correct?
A swell snapshot marks four points: Q at a highest point, R on the rest line, S at a lowest point, and T halfway up a rise. Which letter marks a trough?
Point R sits exactly on the rest line of a wave snapshot, halfway between a crest and a trough. What is R?