1Waves transfer energy
Drop a stone in a pond and ripples spread out. A duck on the water bobs up and down but stays where it is: a wave transfers energy, not water.
waveenergy
Lesson 9.1 notes
What is a wave?
Waves transferring energy, transverse and longitudinal waves, amplitude, wavelength and frequency, reflection and superposition.
2Transverse waves
In a transverse wave the vibrations are at right angles to the direction the wave travels, like a wave on a rope or ripples on water.
transverse
3Longitudinal waves
In a longitudinal wave the vibrations go back and forth along the direction the wave travels, like a push along a slinky. Sound is longitudinal.
longitudinal
4Amplitude and wavelength
The amplitude is the height from the middle line to a crest. The wavelength is the length of one whole wave, for example from crest to crest.
amplitudewavelength
5Frequency
The frequency is the number of waves passing a point each second. It is measured in hertz (Hz): 3 waves passing each second is 3 Hz.
frequencyhertz
6Reflection
Water waves that hit a harbour wall bounce back: they are reflected. That keeps the water inside the harbour calm for the boats.
reflected
7Waves add up
When two waves meet they add together: superposition. A crest on a crest makes a bigger crest; a crest on an equal trough cancels out.
superposition
Explore: Wave machine
Make waves on a rope or a slinky. Change the amplitude and the frequency, and watch what happens to the wavelength.
Common mistake: A wave does not carry the water along with it
The water, rope or air only vibrates around the same place (up and down, or back and forth). It is the energy that travels along with the wave.
Remember
- Waves transfer energy from place to place without carrying the material along with them.
- Transverse waves vibrate at right angles to the direction they travel; longitudinal waves vibrate along it.
- Amplitude is the height from the middle line to a crest; wavelength is the length of one whole wave; frequency is waves per second, in hertz (Hz).
Going further at GCSE
GCSE: Transverse and longitudinal waves → GCSE: Waves revision →