# Quick Question on maximum pressure change in a stationary wave

1. Nov 22, 2009

### qazxsw11111

I always thought antinodes were the areas of greatest pressure change as they shift to and fro, reaching maximum amplitudes at both sides. However, one of the questions asked me and the answer says that nodes are the areas of greatest pressure change.

Can anyone help? Im confused with this. Thanks.

2. Nov 22, 2009

### Redbelly98

Staff Emeritus
It sounds like they are calling nodes the locations of zero velocity, which is where the pressure change is greatest.

3. Nov 22, 2009

### qazxsw11111

But 0 velocity=greatest pressure change?

Im really confused.

4. Nov 25, 2009

### Redbelly98

Staff Emeritus
Sorry about the delayed reply, it is difficult to explain this further without figures. I found this, which helps show what I'm talking about:
http://www.walter-fendt.de/ph14e/stlwaves.htm

On that page, "both sides open" should be selected. We'll look at two parts of the tube, the center and the ends.

At the center of the tube: the molecules do not move at the very center, so velocity is zero. However, you'll also notice that the molecules surrounding the center alternate between bunching together and spreading apart. So the pressure (which corresponds directly with the density or closeness of the molecules) has a maximum change there.

At the ends of the tube, the molecules are moving back and forth with maximum velocity change. However, their spacing stays the same, indicating zero change in pressure.

Hope that helps!