Longitudinal Waves: Compression or Rarefaction at Displacement 0?

[duckandcover]

Why is it that when a longitudinal wave is represented by a (pressure/position) and a (displacement/position) graph does the displacement 0 represent a compression or rarefaction
(maximum or minimum pressure)?

 

[turin]

You can think of it as the average of what the molecules are doing there. The compression peaks occur where the molecules are coming together, so the displacements of the molecules are all directed towards that point and they average out to zero. Similarly for rarefaction, except that they are direcected away from that point.

 

[duckandcover]

You can think of it as the average of what the molecules are doing there. The compression peaks occur where the molecules are coming together, so the displacements of the molecules are all directed towards that point and they average out to zero. Similarly for rarefaction, except that they are direcected away from that point.

thanks that clears it up