Waves transfer energy without transferring matter.
Transverse waves: oscillations are perpendicular to the direction of energy transfer. Examples include light, water waves, and all electromagnetic waves.
Longitudinal waves: oscillations are parallel to the direction of energy transfer. Examples include sound waves and ultrasound — they consist of compressions and rarefactions.
The wave equation links speed, frequency and wavelength:
v = fλ
Period is the time for one complete wave:
T = 1/f
Key definitions:
Wavelength (λ) = distance between two identical points on consecutive waves
Frequency (f) = number of waves passing a point per second (Hz)
Amplitude = maximum displacement from the rest position
Crest (peak) = the highest point of a wave
Trough = the lowest point of a wave