# Wave speed as a function of compression?

1. Apr 9, 2012

### PhysicsMike

Dear physics forum, I am doing an experiment on the vibrational behavior of beams and a question has come up that I can't answer. How does compression affect wave speed?

Brief overview of the experiment:

studying the change in vibrational behavior of a beam that is gradually tapered toward a point (equilateral triangle). Basically I have four beams:
Beam 1: uniform rectangle
Beam 2: tapering begins
Beam 3: more tapering
Beam 4: beam comes to a point at one end.

The beams are clamped at one end, with the other end open. If you take the ground to be the 'x-axis', then the length of the beam is in the 'x-axis', the width in the 'z-axis', and the height in the 'y-axis'. Aka the beam, which is quite flexible (synthetic trim board), does not sag due to gravity.
Their is a sin-wave generator located 100mm from the clamped end. I've found that even when i hang the beam, or stand it up (clamp closest to ground), the node placement does not change. What i have found, is that the wavelength decreases the farther i get from the clamped end, aka the wave speed is decreasing.
basically i've got compression on the bottom and tension on the top of the beam. I know v=sqrt(T/u), but does anyone have any insight into wave speed as a function of compression?

any insight is welcome, thanks

2. Apr 11, 2012

### gomunkul51

Is the beam made out off two parts of which one is under tension and the other under compression? Or what is being compressed by what?

Roman.

3. Apr 11, 2012

### Khashishi

If you are talking about sound waves, the speed of sound depends on the bulk modulus. See https://en.wikipedia.org/wiki/Speed_of_sound
I suppose if most materials are compressed, the bulk modulus will increase, so the sound speed should increase.

4. Apr 11, 2012

### Khashishi

If you are talking about sound waves, the speed of sound depends on the bulk modulus. See https://en.wikipedia.org/wiki/Speed_of_sound
I suppose if most materials are compressed, the bulk modulus will increase, so the sound speed should increase.