Transverse & Longitudinal Waves

What a wave is

• A wave is an oscillation (vibration) that transfers energy from one place to another without transferring matter
• Waves can also carry information: sound carries speech, radio waves carry television and radio signals
• Waves may be either transverse or longitudinal. The difference is the direction of the oscillations compared with the direction the wave travels

Transverse waves

• In a transverse wave the oscillations are perpendicular (at right angles) to the direction of energy transfer
• Examples: ripples on a water surface, waves on a rope or string, and all electromagnetic waves (light, radio, X-rays)
• A transverse wave has peaks (crests) and troughs

Longitudinal waves

• In a longitudinal wave the oscillations are parallel to the direction of energy transfer
• Longitudinal waves show areas of compression (particles close together, high pressure) and rarefaction (particles spread out, low pressure)
• Sound waves travelling through air are longitudinal. So are P-waves from earthquakes and the waves along a slinky pushed back and forth

It is the wave that travels, not the medium

• The medium (the water or the air) oscillates about a fixed position; only the wave and its energy move along
• Evidence for water: a floating cork or duck on a pond bobs up and down as ripples pass but is not carried along with the ripple
• Evidence for sound: a candle flame or a light piece of paper in front of a loudspeaker flickers or vibrates back and forth but is not blown away; the air does not rush from the speaker to your ear