A WAVE is a transfer of ENERGY from one place to another WITHOUT transferring matter.
The particles (or fields) oscillate — they don't travel with the wave.
The WAVE PATTERN travels; the MEDIUM stays in place.
Evidence:
Ripples on water: a floating cork bobs up and down but doesn't travel forward.
Sound wave: air molecules vibrate back and forth but don't travel with the sound.
Waves transfer energy — this is why sound can move a speaker cone, light can heat objects, and water waves erode cliffs.
Transverse Waves
TRANSVERSE WAVES: the oscillation (vibration) is PERPENDICULAR (at right angles) to the direction of wave travel.
EXAMPLES:
Light and all electromagnetic waves — electric and magnetic fields oscillate perpendicular to travel direction.
Ripples on water surface — water moves up and down; wave travels horizontally.
Waves on a string or rope — string moves up and down; wave travels along the string.
Seismic S-waves.
DRAWING: shows a sinusoidal wave — peaks and troughs.
The DISPLACEMENT of the medium is perpendicular to the direction of energy transfer.
CAN travel through vacuum — light reaches us from the Sun through empty space.
Longitudinal Waves
LONGITUDINAL WAVES: the oscillation is PARALLEL to (along the same direction as) the direction of wave travel.
EXAMPLES:
SOUND waves in air (or any medium) — most important example.
Ultrasound — longitudinal pressure waves above 20,000 Hz.
Seismic P-waves.
Compression waves in a spring.
MECHANISM:
Particles are pushed closer together (COMPRESSION) and pulled further apart (RAREFACTION) alternately.
Compressions = high pressure regions. Rarefactions = low pressure regions.
The pattern of compressions and rarefactions travels forward — the particles only vibrate back and forth.
CANNOT travel through vacuum — sound needs a medium (particles to compress).
In space, no one can hear you scream.
⚠️ Common Mistake
In a TRANSVERSE wave, the oscillation is PERPENDICULAR to the direction of travel — not parallel. In a LONGITUDINAL wave (like sound), the oscillation is PARALLEL to the direction of travel. Don't confuse the two.
📌 Key Note
Waves transfer energy, not matter. Transverse: oscillation ⊥ direction (light, water ripples, EM waves). Longitudinal: oscillation ∥ direction (sound, ultrasound). Longitudinal shows compressions and rarefactions. Sound needs a medium; light does not.
🎯 Matching Activity — Wave Types
Sort each wave into transverse or longitudinal. — drag the symbols on the right to match the component names on the left.
Transverse
Drop here
Transverse
Drop here
Longitudinal
Drop here
Longitudinal
Drop here
Transverse
Drop here
Sound in air — air molecules compressed and rarefied in direction of travel
All electromagnetic waves — can travel through a vacuum
Ultrasound — pressure waves with compressions and rarefactions
Light — electric field oscillates perpendicular to direction of travel
Water ripples — water surface moves up and down, wave moves horizontally
🧪 Required Practical
🔬 RP19 (Physics) — Investigate the slinky spring to demonstrate transverse and longitudinal wave motion. RP20 — Ripple tank to observe wave properties.
Know the method, variables, equipment and how to analyse results.
🎯 Test Yourself
Question 1 of 2
1. How do particles move in a longitudinal wave compared to the direction of wave travel?
2. Why can light travel through a vacuum but sound cannot?
⭐ How Well Do You Understand This Topic?
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