This was another one of those things I wrote on my "To Do" list and figured I should complete before it had been on there a year.
On the day my AP Physics C students learn about torsional (twisting) pendulums I had written myself a note that while they "got it" they were having problems visualizing it. I didn't know how to construct one so I started an internet search and found a lot of problems about them but not a lot of demos. I found one video that looked promising and took a still to help guide my trip to the hardware store. The description called it a chuck nut which didn't seem quite right. After asking for help on Twitter I got a response:
He was nice enough to offer some advice and a link to the part he used. Once I knew what the part was actually called it was much easier to find them. When looking for the right pinch vise I looked for ones sold individually (most are in sets) and checked the range that it could hold. Many can securely hold amazingly small pieces so you have to also check out the max that they can hold. I settled on these, fairly cheap and should be versatile.
I showed students the golfball oscillating with the fishing line, nichrome and steel wire in class. A video of each is below. We did not calculate anything (the wires were really bent) but it worked as a qualitative experiment.
Afterwards I tried making some more with different masses, a small brass mass and a large rubber stopper. The tricky part is attaching the steel cable so that it doesn't twist within the object. I added hot glue to the brass mass but its not as secure as I would like. I added a black line in sharpie to the mass so the oscillation was easier to see. For the rubber stopper I was able to stab the cable through the stopper, although drilling a hole may have been more precise. I added a white pushpin to the side so that we could see the oscillation better. For these last two versions I only needed one pinch vise at the top to hold the cable.
All in all I really liked the way it turned out and it helped students to visualize what was happening with their problems. It can always be improved but at least I have another year until I need it again.