Waves and energy – energy transfer
In a wave, the material on which the wave is travelling is moving. However, the material itself does not move along with the wave.
Demonstrating longitudinal and transverse waves
The video shows a hand making longitudinal and transverse waves on a slinky. The audio describes longitudinal and transverse wave characteristics.
Consider the transverse wave on a slinky. Any given part of the slinky is moving up and down, but the wave is travelling along the slinky. Energy also travels along the slinky. Waves transfer energy from one place to another.
Visualising the relationship between waves and energy
To understand how energy and waves work, consider two people holding a slinky between them. The people holding the slinky provide the energy to make waves.
Wave patterns
Patterns of standing waves.
People holding the slinky supply the energy to make the patterns. To make pattern 1, people have to shake the slinky back and forth at a certain speed. To make pattern 2, the slinky has to be moved back and forth faster (higher frequency). To make pattern 4, the people need to move the slinky back and forth much faster. It is much easier to make pattern 1 than pattern 4 because it takes less energy. This illustrates the relationship between frequency and energy – the higher the frequency, the higher the energy.
Wavelengths and frequency
In pattern 1, there is one complete wave. Pattern 3 has two complete waves, and pattern 4 has 2.5 complete waves. This shows the relationship between frequency and wavelength. The higher the frequency, the shorter the wavelength. The relationship between wavelength and frequency is called an inverse relationship, because as the frequency increases, the wavelength decreases.
Energy and amplitude
Patterns 5 and 6 have the same wavelength and frequency but the amplitude is different. To make pattern 6, people have to move the slinky back and forth further than for pattern 5. It takes more energy to make pattern 6 than to make pattern 5. This illustrates the relationship between energy and the amplitude of a wave. The higher the amplitude, the higher the energy.
To summarise, waves carry energy. The amount of energy they carry is related to their frequency and their amplitude. The higher the frequency, the more energy, and the higher the amplitude, the more energy.
You can make these patterns yourself with the activity Investigating waves and energy.
Nature of science
The illustrations in this article are models of waves. A model is a representation of an object, idea, system or process. Learning to make sense of models and diagrams is part of the science capability ‘Interpret representations’.
Related content
The article Waves and energy – wave basics provides additional information about transverse and longitudinal waves, including vocabulary.
The article Waves as energy transfer provides more in-depth information for students working at higher curriculum levels.
The activity Making Mexican waves demonstrates wave energy and wave behaviours.
