# Wave Velocity in Terms of Tension

1. May 23, 2008

### bfr

A few friends and I built a wave "machine." It's made by laying out brass "rods" about a foot long next to each other about an inch or so apart on tape, and then taping the top side. When holding both sides of this "machine," when one strikes one rod at one end, it makes the rod in front of it move, which makes the rod in front of it move etc., creating a "wave."

For a wave like this, is there any way to determine the wave velocity in terms of a changing tension (which would be changed by pulling on either side of the wave "machine" more or less).

2. May 23, 2008

### rock.freak667

well

$$v=\sqrt{\frac{T}{\mu}$$

where $\mu$ is the mass per unit length.

3. May 23, 2008

### Redbelly98

Staff Emeritus
Neat. Can you tell us a ballpark estimate of the wave velocity you get in practice? I've wanted to build something like this as I am a private tutor and would like to have a wave motion demo for students. With the spring I have used the waves just move too fast to watch.

4. May 23, 2008

### bfr

My friend calculated that the wave moved anywhere from about 30cm/s to to 130cm/s when we varied how hard we pulled on each side (he got these velocities by timing the waves). It looked kind of fast. The entire medium was relatively short (70cm maybe), though, which made it harder to time and made it look like it went by faster, and we used duct tape, which because of its width, probably also sped up (and dampened) the wave (we did this though because otherwise some rods would be lopsided with thinner tape).

rock.freak667: OK, thanks.

EDIT: Quick question - do you think changing the concentration of rods / distance between each rode would increase or decrease the wave velocity?

Last edited: May 23, 2008