Choose the correct snapshot graph longitudinal waves

[firezap]

Homework Statement

http://i.imgur.com/4dL6TQY.jpg

I don't know how to read the figure or the graphs. O_O

 

[Quantum Defect]

Homework Statement

http://i.imgur.com/4dL6TQY.jpg

I don't know how to read the figure or the graphs. O_O

I think that D is the displacement from equilibrium. Negative D ==> closer than equilibrium, Positive D ==> greater than equilibrium spacing. D = 0 ==> equilibrium spacing
The first two "atoms" are spaced 1 cm apart, which is equal to the equilibrium spacing. From these clues, it looks like "a" to me, but things look screwy to me after the first four cm... It would help to know how D is being calculated...

 

[firezap]

It's a. I look at the graph at x = 3cm and displacement = -1cm. The dot would move left 1cm, so the dot is at 2.

 

[SammyS]

It's a. I look at the graph at x = 3cm and displacement = -1cm. The dot would move left 1cm, so the dot is at 2.

Yes, it's a.