Transverse and longitudinal waves
Two ways to make a wave
- Shake a rope up and down — the wiggle runs along it.
- Push and pull a slinky end-on — a squash runs along it instead.
- Both carry energy, but the particles move in different directions.
Transverse waves
- The particles vibrate perpendicular to the direction the energy travels.
- Examples: a wave on a rope, all electromagnetic waves, ripples on water.
Practice
In a transverse wave, the particles vibrate:
Transverse = vibration at right angles to the energy flow (a rope wave, light, water ripples).
Longitudinal waves
- The particles vibrate parallel to the direction of travel.
- Made of compressions (squashed together) and rarefactions (spread out). Sound is longitudinal.
Practice
Sound travelling through air is a longitudinal wave.
Yes — the air particles vibrate back and forth along the travel direction, making compressions and rarefactions.
Practice
Select all the waves that are transverse.
Light, water ripples and a rope wave are transverse. Sound and an end-on slinky wave are longitudinal.
Practice
A longitudinal wave is made of compressions and ____.
Compressions are where particles bunch up; rarefactions are where they spread out.
Two graphs
- Displacement–distance (a snapshot of the whole wave) → read the wavelength.
- Displacement–time (one point over time) → read the period.
- Both look like sine curves, for either type of wave.
Practice
Match each graph to what you read off it.
A snapshot against distance shows the wavelength; one point watched over time shows the period.
You've got it
Key idea
- transverse: vibration perpendicular to travel (rope, light, ripples)
- longitudinal: vibration along travel — compressions & rarefactions (sound)
- displacement–distance shows $\lambda$; displacement–time shows $T$