Longitudinal travelling wave
Another version with the graphs of vt and DPt shown
Related Applets:
Traveling waves and Standing waves
Compare compressions/rarefactions in a longitudinal travelling wave with crests/troughs in a transverse travelling wave
Crests/troughs
in a transverse travelling wave

Compressions/rarefactions
in a longitudinal travelling wave


(1) Separation

The separation between two adjacent crests or troughs
is the wavelength.

The separation between two adjacent compressions or
rarefactions is the wavelength.

(2) Displacement from equilibrium
position

The greatest

Zero 
(3) Speed 
Zero 
The greatest

The displacements at a certain instant along a longitudinal travelling wave: