This was a fun lab, but had a few issues.

We had two groups using water and two groups using acetone (the “hot” and “cold” groups). Next time round, I think I'll switch to only using water, as it was much easier to deal with, although we might need more than the two electric tea kettles we used. Because the water is easier to deal with, it's easier to accumulate more data.

The students were told to start by taking tension versus length curves at a variety of (fixed) temperatures (maybe every 10 degrees?), and then they took a long constant-length run as the water cooled or acetone warmed. However, they had trouble changing the length fast enough to keep the temperature constant when they changed the length, which was a pain. I suspect they might do better by taking tension vs temperature curves at each length they study. This will mean they have to get the temperature to change more quickly than an hour if they want to do any reasonable set of lengths.

Regarding the analysis, I was disappointed to find that most of the groups had sign errors somewhere in their calculation of the change in internal energy for the isothermal stretch. I think this part of the analysis might benefit from giving them a chance to work it through in class where they can get feedback.

David

This year I had all students use hot water and ice, which was simpler. The lab went pretty smoothly on the whole. The tricky part was finding rubber bands that didn't show too much hysteresis (i.e. after stretching them and returning to the original length, the tension returned to the same value).