Parts of a wave diagram

What this diagram shows

A wave carries energy from one place to another without carrying matter along with it. Water waves, sound and light are all waves. This diagram shows a transverse wave, the up-and-down shape most people picture, with four parts to learn. In Explore, tapping a part gives its name and a short explanation. Labels names all four. Quiz me asks the student to find each part and gives a score at the end of the round.

• Crest: the highest point of the wave.
• Trough: the lowest point of the wave.
• Wavelength: the distance from one point on a wave to the same point on the next, such as crest to crest.
• Amplitude: the distance from the rest position (the middle line) to a crest or a trough. A bigger amplitude means more energy.

Common misconceptions

The most common mistake on tests is measuring amplitude from the trough to the crest. That distance is twice the amplitude. Amplitude is measured from the rest position, the flat middle line the wave would sit on if there were no wave, up to a crest or down to a trough.

A second big idea is that the wave moves but the water does not travel with it. A floating duck bobs up and down as a wave passes and ends up roughly where it started. Students also mix up wavelength with height, or think wavelength can only be measured crest to crest. Any matching pair of points works, such as trough to trough. Finally, not all waves look like this picture: sound waves are longitudinal, made of squashed and stretched regions, although they still have a wavelength and amplitude.

Where this fits in school

• US, grade 4: NGSS 4-PS4-1 asks students to model waves to describe patterns in amplitude and wavelength, and that waves can cause objects to move.
• US, grades 6 to 8: NGSS MS-PS4-1 asks students to use a simple model of waves showing how amplitude is related to the energy a wave carries.
• England, Key Stage 3: pupils study waves on water as transverse undulations, sound waves and their frequency in hertz, and light waves.
• England, GCSE (Years 10 and 11): students use amplitude, wavelength, frequency and period, and the wave equation (wave speed = frequency × wavelength).

A 10-minute waves activity

• Ask the student to draw a wave and label any parts they know, before opening the diagram.
• In Explore, tap all four parts. Compare with their drawing and correct any labels.
• Focus on amplitude. Ask: "If I measure from the bottom of a trough to the top of a crest, what have I measured?" (twice the amplitude).
• Link to energy: a gentle ripple and a large ocean wave differ in amplitude. Which carries more energy?
• Finish with a Quiz me round.

A jump rope or a long piece of string makes a good physical model. Tie one end to a chair leg and flick the other end up and down. Small flicks make a low amplitude; bigger flicks make a higher amplitude. Flicking faster makes more waves and a shorter wavelength.

Learning more

Science is part of Eurekami's skill map, with lessons that draw science diagrams live and narrate them in English or Spanish. For older students, Exam Prep includes GCSE Combined Science practice papers.