- First, from Mark Hammond, the idea of just hanging a wire from an I beam in the ceiling, putting a pointer on it, and measuring. I hadn't gotten around to trying this, but I was thinking that it'd be a good last-ditch substitute.
- Second, from Aaron Titus (do you have a blog Aaron?), the idea of doing that but with a motion detector underneath the mass hanger. If the wire stretches enough, this will measure the distance more accurately than the first method (which is apparently possible - I thought that the stretch wouldn't be much relative to the motion detector's resolution, but I guess that I'm underestimating one of the two).
- Third, also from Aaron, attach one end of the wire to a clamp, run it horizontally (I ran it a little more than 6 meters to maximize the stretch amount) over a Pasco rotary motion sensor. Have a short length of wire hanging over the pulley and wrapped around a mass hanger. It only took about 500 g of mass to get a nice range of stretch. Even a 50 gram difference caused an easily measurable stretch for the sensor (around .05 radians/50 grams).
For the third method:
- No knots: wrap the wire around both connection points - you don't want kinks and knots slipping.
- I measured the tension force with a force probe as well as calculating it from mg. They were pretty equivalent in practice (as well as in theory, of course), so I'll just use mg.
- I used thin enameled magnet wire (.17 mm diameter - don't know the gauge); I'd like to get aluminum wire as well, so that I can predict resonant frequencies for the singing rods.
- Edit: put a catch box underneath. As I was writing this, the wire gave way with 500 g hanging from it.
- Here's the data - 118.9 GPa (117 on Wikipedia). I'll surely take that. I'll use this to predict v for a transverse wave, too, and see if I can get agreement there, but this is seriously encouraging.