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
Ultrasound — pressure waves with compressions and rarefactions
Light — electric field oscillates perpendicular to direction of travel
All electromagnetic waves — can travel through a vacuum
Water ripples — water surface moves up and down, wave moves horizontally
Sound in air — air molecules compressed and rarefied in direction of travel
🧪 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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