Nine - Wave Motion
1. describe that progressive waves are waves that propagate from its source to another place,
transferring energy from one place to another through a medium (except EM)
2. describe that mechanical waves need a medium to travel through, e.g. sound, seismic, water
3. describe that longitudinal waves oscillate/move particles parallel to the direction of
propagation
a) shows compressions (areas of
high density) and rarefactions
(areas of low density)
b) shows the wave graphically
compressions- regions in sound
wave where air pressure is greater
than its mean value
rarefactions- regions in sound wave
where air pressure is less than its
mean value
e.g. p-seismic and sound
4. describe that transverse waves oscillate/move particles perpendicular to the direction of
propagation
e.g. s-seismic or EM waves
5. define the following terms as:
- displacement: the distance from a given point on the wave to its equilibrium/rest point
- amplitude: the maximum displacement from
equilibrium/rest point on a waves, measured in
metres
- wavelength: the smallest distance between
one point on a wave and the identical point on
the next wave, measured in metres. symbol λ
- period: time taken to complete one full
wavelength/cycle. measured in seconds.
symbol T.
- frequency: the number of oscillations
passing a point per second, measured in
Hertz. symbol f.
1
calculated using 𝑓𝑟𝑒𝑞𝑢𝑒𝑐𝑦 = 𝑝𝑒𝑟𝑖𝑜𝑑
-speed of a wave: the distance travelled by a
point on a wave per unit time
6. derive from the definition of speed, frequency and wavelength, the wave equation v = fλ
a) in one second, f waves are produced, each of one wavelength λ, distance travelled by first
wave in one second v= fλ.
b) speed = distance / time
so the speed of the wave is given by wavelength/time it takes for 1 wavelength (period).
so v = wavelength/period and
period = 1/frequency
so v = wavelength / 1/frequency = wavelength * frequency
v = wavelength * frequency
7. explain that reflection is when waves rebound from a barrier/surface, changing direction but
remaining in the same medium
8. explain that refraction is the change in direction of a wave when it travels from one medium
to another, caused by a change in speed.
-more dense -> slower speed -> shorter wavelength as v ∝λ
- frequency cannot change, because it is predetermined by the source
9. explain that diffraction is the spreading of a wave when it passes through a gap (aperture) or
around a corner/ edge of an object.
- aperture must be comparable to the wavelength of wave for diffraction
-when aperture >> λ, small diffraction
-when aperture > λ, medium diffraction
-when aperture = λ, most diffraction