Waves & Energy Transfer (SQA National 5 Physics): Revision Note
Exam code: X857 75
Waves & energy transfer
What is a wave?
A wave is something that transfers energy from one point to another without transferring matter
For sound waves, this means it is the wave and not the air molecules (the matter) that travels
Objects floating on water provide evidence that waves only transfer energy and not matter
It is possible to see objects on the surface of the water bob up and down but not change their position
This is because the wave and not the water (the matter) itself that travels
Waves are described as oscillations or vibrations about a fixed point
For example, ripples cause particles of water to oscillate up and down
Sound waves cause particles of air to vibrate back and forth
Worked Example
The diagram below shows a toy duck bobbing up and down on top of the surface of some water, as waves pass it underneath.
Explain how the toy duck demonstrates that waves do not transfer matter.
Answer:
The toy duck moves up and down, but does not travel with the wave along the surface of the water
The water waves transfer energy, but the water particles do not move
This means when a wave travels between two points, no matter travels with it, the points on the wave vibrate up and down about fixed positions
Objects floating on the water bob up and down when waves pass under them, demonstrating that there is no movement of matter in the direction of the wave, only energy
Examiner Tips and Tricks
There is a key distinction between the particles (or oscillations) of a wave and the wave itself.
The motion of the wave causes the particles to move. The particles themselves are not the wave.
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