Transverse vs Longitudinal Waves
Transverse Wave
The medium oscillates perpendicular to the direction the wave travels — like a flicked rope, where the rope moves up and down while the pulse moves forward. Light is a transverse wave.
Unit: meter/second (m/s)
Example: Shake a rope up and down: crests and troughs travel along the rope while each bit of rope only moves vertically.
Longitudinal Wave
The medium oscillates parallel to the direction of travel — compressions and rarefactions, like sound in air, where air molecules bunch up and spread out along the path.
Unit: meter/second (m/s)
Example: Clap your hands: air molecules surge back and forth along the direction the sound travels — no air actually travels to your ear.
Key differences
| Aspect | Transverse Wave | Longitudinal Wave |
|---|---|---|
| Oscillation vs travel | Perpendicular | Parallel |
| Structure | Crests and troughs | Compressions and rarefactions |
| Polarization possible? | Yes — the oscillation direction can be filtered | No — only one oscillation axis exists |
| Needs a medium? | Light needs none; mechanical transverse waves need a solid or surface | Always needs a medium (solid, liquid, or gas) |
| Examples | Light, rope waves, stadium wave | Sound, slinky push-pull, seismic P-waves |
Sound can't be polarized, and that single fact proves it's longitudinal — a transverse wave's sideways wiggle has a direction you could filter, but sound's back-and-forth has no 'side' to block. Polarized sunglasses only work because light is transverse.