Procedural Notes
- You can make the students measure the spindle diameter using the Vernier calipers, but unless you have already taught them how to read those calipers, this alone will take the entire lab period. Nothing bad happens if they all use the same value, d = 0.23cm, for the spindle diameter.
- Try to have the students measure the brass rod first. It is is harder to get good results with the brass, and the likeliest explanation is slipping. The brass rods are smoother than the iron rods, and can slip over the spindle instead of smoothly rolling it.
- Once the spindle gets wet (when steam starts pouring out of the first rod), you increase the likelihood of slipping. If you don't remind the students to dry the spindle, or if they forget, the second rod is more likely to slip. If the econd rod is brass, it's almost a given that it will slip.
- Remind the students to position the spindle so that the needle does not scrape against the face of the protractor. The needle will catch and stop the spindle from rolling smoothly.