Physics 11 – After a few classes of thinking and discussing concepts, it was time to do some concrete work on forces. The students examined the relationship between spring force and spring extension. They were tasked with designing their own test procedure, gathering data, and graphing it to come up with a model for springs. Several groups didn’t measure spring extension but measured the total length of the spring. While they could have subtracted the initial length, they didn’t. This is the problem with verbal instructions – there will always be students that miss out on details. From their perspective, there would be no obvious reason why they want to use extension data rather than total length.
I haven’t gone over their labs yet. My general plan is to give feedback to each student, including a checklist of things to look for such as: titles and headings, data table and observations, repeatable and understandable procedure, graphs and data analysis, and a decent conclusion and discussion. They already have a report format sheet and I’ll hand out an exemplar for this lab. The next time they hand in a lab report, they can be graded against a similar checklist and there will be no questions about expectations.
BC Physics 180 
I don’t see what’s so bad about F vs L instead of F vs dL … slope will still give spring constant, and now the intercept has physical meaning (initial length). It’s not much different than starting a motion not at the origin.
LikeLike
Yes, you’re right. I think the big difference is interpreting what the intercepts tell us. So if you graph force vs extension, the y-intercept tells you how much pre-load is on the spring. But if you graph spring length of a spring with a lot of pre-load, we need to recognize that the x-intercept of the trend line does not represent the initial length. Either way is fine, as long as we give it some critical thought.
LikeLike
Yeah I realized a little after I posted that I switched it up. 🙂
LikeLike