# Determine the direction of movement of a point on wave

1. Jan 19, 2012

### songoku

1. The problem statement, all variables and given/known data

The figure shows a longitudinal wave moving to the right. Indicate the direction of motion of the points A and B

2. Relevant equations

3. The attempt at a solution
How to determine the direction; either to the left or right?

Thanks

2. Jan 19, 2012

### Spinnor

If not told the direction the wave was traveling the sketch could be three things, a longitudinal wave traveling to the left or traveling to the right, and also a standing longitudinal wave.

3. Jan 19, 2012

### songoku

It is given in the question, the wave is moving to the right. However, I still don't know how to determine the direction of movement of the points :tongue:

4. Jan 19, 2012

### Spinnor

Let the density of your wave material be,

ρ = 1 + Δcos(x - t) where Δ << 1

dρ/dt = - dJ/dx --> J = Δcos(x - t) ?

Where the density peaks the velocity peaks in the forward direction and where the density is minimum the velocity peaks in the backwards direction, see,

http://lifgarbagez.ucdavis.edu/~dmartin/phy7/7C/java/longitudinal.html [Broken]

Make the wave go to the right and slow it down.

Last edited by a moderator: May 5, 2017
5. Jan 19, 2012

### songoku

Sorry I haven't covered about the density of wave material and I don't have the plugin to open the link given; I'll try to install it later.

Is there any easier way to explain point A moves either to the left or right? Because this is actually lesson for eight grade (second year of middle school)

Last edited by a moderator: May 5, 2017
6. Jan 26, 2012

### songoku

My best guess is that A and B is compression and it will turn to rarefaction so A will move to the left and B to the right...but that's just pure guess