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 [itex]\lambda[/itex], but in the drawing just underneath it, the Kunt pipe, the distance between two successive heaps of cork is [itex]\lambda/2[/itex], 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 [itex]\lambda/2[/itex] 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: [itex]\lambda=u/f[/itex] 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 [itex] \lambda/2[/itex] distance.