On a longitudinal wave:
- A compression is a region where particles are close to one another. (High pressure)
- A rarefaction is a region where the particles are further apart. (Low pressure)
For a longitudinal wave at an instant of time,
- displacement is zero when the particle is at equilibrium position
- displacement is positive when the particle is displaced to the right of its equilibrium position
- displacement is negative when the particle is displaced to the left of its equilibrium position
