# Longitudinal standing waves in gas

1. Oct 5, 2014

### Karol

1. The problem statement, all variables and given/known data
In the uppermost drawing is a propagating wave. the distance between two successive high pressure areas, as seen in the picture, is the wavelength $\lambda$, but in the drawing just underneath it, the Kunt pipe, the distance between two successive heaps of cork is $\lambda/2$, why?
The Kunt pipe is filled with thin cork powder and when there are standing waves the cork piles in the nodes, denoted N in the drawing.
I understand the distance between two successive nodes is $\lambda/2$ in transverse waves, but why in longitudinal waves? the mechanism is different.
And what's the mechanism? is a molecule swinging back and forth between two nodes, the third drawing from above? the nodes, i understand, are high pressure areas. the molecules don't move in them so the cork piles there.
In the 2 lowest drawings i ask if the high pressure areas change place each half period time between the nodes.

2. Relevant equations
The velocity of waves: $\lambda=u/f$

3. The attempt at a solution
If my explanation is right and the molecules on each side of each node, a high pressure area, oscillate in opposite directions and if the nodes change places as in the lowest drawings then there is a difference between the successive nodes and that explains the $\lambda/2$ distance.

#### Attached Files:

• ###### Snap1.jpg
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2. Oct 10, 2014