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Describing a Wave

Measure and Compare Wavelength

Review the diagram below on the left. Then look at the picture to the right. Notice that wavelength can be measured two ways—from peak to peak and from trough to trough.

Describing a Wave
A labeled diagram of waves.
A line cuts across the middle of an up and down shape of a curvy line that represents waves. The line that cuts across the middle is called “the resting position.” The top part of a wave is called the peak. The bottom part of the wave is called the trough. The wavelength of a wave is shown as the distance from one peak to the peak next to it. The wavelength is also shown as the distance from one trough to the trough next to it. The distance from peak to peak is equal to the distance from trough to trough.

Measuring Wavelength on a Rope
A labeled diagram of a child making waves with a rope that is tied to a tree.
A dotted line cuts across the middle of the waves to show the resting position. The wavelength from peak to peak, or the top of one wave to the top of the wave next to it, measures six feet. The wavelength from trough to trough, or the bottom of one wave to the bottom of the wave next to it, also measures six feet.

Compare Waves

Click the Arrange It button on the right to get started.

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