Transverse and Longitudinal Waves

Waves are classified by the direction of the oscillations compared with the direction in which the wave transfers energy.In a transverse wave the oscillations are perpendicular to the direction of energy transfer. Examples are waves on a string, ripples on water and all electromagnetic waves, in which the electric and magnetic fields oscillate at right angles to the direction of travel. A transverse wave has crests and troughs.In a longitudinal wave the oscillations are parallel to the direction of energy transfer. Sound is the main example. The particles move back and forth along the direction of travel, forming compressions, where they are closer together than normal and the pressure is higher, and rarefactions, where they are further apart and the pressure is lower. Sound needs a medium, so it cannot travel through a vacuum.A slinky spring can show both types. Moving one end from side to side sends a transverse wave along it; pushing and pulling the end along its length sends a longitudinal wave.For both types the wavelength is measured between equivalent points: crest to crest for a transverse wave, and from the centre of one compression to the centre of the next for a longitudinal wave. The wave equation v = fλ applies to both.Example: compressions on a slinky are 0.40 m apart and the end is pushed back and forth at 2.5 Hz, so the wave speed is 2.5 × 0.40 = 1.0 m s^-1.