1. Types
   1. Transverse
      1. perpendicular to direction of vibration
   2. Longitudinal
      1. parallel to direction of vibration
         1. Sound
2. Terms
   1. amplitude
      1. a
      2. greatest displacement from rest
   2. frequency
      1. f
      2. numper passed a fixed point per second
   3. wavelength
      1. λ
      2. distance from one crest to next
   4. Velocity
      1. C
      2. frequency × wavelength
      3. C = f × λ
3. Interference
   1. constructive
      1. two waves combine
      2. bigger wave
   2. destructive
      1. two waves combine
      2. smaller wave
   3. coherent
      1. two waves combine
      2. same frequency
      3. in phase
      4. wipe out of wave
4. Diffraction
   1. spreading of waves into geometric shadow of an obstacle
   2. Longer the wavelength, greater the diffraction
   3. nλ = d sin θ
5. Polarisation
   1. only transverse
   2. confine vibrations to one plane