Longitudinal Waves
* Particle motion: Particles in the medium vibrate parallel to the direction the wave travels. Think of a slinky: When you push one end, the coils compress (push together) and then stretch out (move apart) as the wave travels down the slinky.
* Examples: Sound waves, seismic P-waves
Transverse Waves
* Particle motion: Particles in the medium vibrate perpendicular to the direction the wave travels. Think of a rope tied to a wall: If you shake the rope up and down, the wave travels horizontally along the rope, but the individual parts of the rope move up and down.
* Examples: Light waves, water waves, seismic S-waves
Key difference: The direction of particle motion is the key to distinguishing between longitudinal and transverse waves.
