Water waves and superposition
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Explainer Video
Summary
Water waves and superposition
In a nutshell
Waves travel through water by creating ripples which move transversely. Waves can be reflected if they come into contact with a barrier. Superposition happens when two waves meet and either add together or cancel out.
Waves travelling through water
When a pebble is thrown into a lake, ripples are created. These ripples (or undulations) form in circles around the pebble and expand outwards in all directions. This looks like a circle which is increasing in size. This is called a water wave and is an example of a transverse wave.
Transverse waves
A wave that undulates up and down at right angles to the direction the wave is travelling in.
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| Undulations | Repeated movements up and down. |
| Amplitude | The maximum height of a wave, measured from the middle of the undulations. |
| Crest | The highest point of a wave (above the middle). |
| Trough | The lowest point of a wave (below the middle). |
| Wavelength | The length of a wave, measured from crest to crest, or trough to trough. |
Note: You may see crests referred to as peaks in different textbooks. This lesson will refer to the tops of waves as crests.
Reflection
If a wave hits a barrier or surface, it will be reflected. Reflection means that the waves will now travel in a different direction than before.
Water waves are similar to light waves. The angle of reflection when hitting a straight boundary will be the same for both types of wave.
Example
If a pebble was dropped in a swimming pool the water waves would be reflected when they reached the walls of the pool.
Superposition
A superposition happens when two waves meet. Depending on the alignment of the waves, the two waves will either add together or cancel each other out.
If the two waves are aligned crest-to-crest and trough-to-trough, they will add together to form one wave with a larger amplitude. When the two waves have an equal amplitude, the final wave will have double the amplitude of the starting waves.
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If the two waves are aligned crest-to-trough and trough-to-crest, they will instead cancel out to form a flat wave with no undulations. The amplitude of this wave is zero.
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FAQs - Frequently Asked Questions
What type of waves are water waves?
A water wave is an example of a transverse wave. A transverse is a wave that undulates up and down at right angles to the direction the wave is travelling in.
What are the features of a water wave?
Amplitude is the maximum height of a wave, measured from the middle of the wave. The crest is the highest point of a wave (above the middle). The trough is the lowest point of a wave (below the middle). A wavelength is the length of a wave, measured from crest to crest, or trough to trough.
How do water waves reflect?
If a wave hits a barrier or surface, it will be reflected. Reflection means that the waves will now travel in a different direction than before.