Good Intentions, Bad Lab
Posted February 28, 2012on:
A couple of weeks ago we did a lab straight from the textbook. (Here is the Lab Instructions, typed up and put it into my words.) I’d been looking for a good Conservation of Energy Lab. I wanted to use the Vernier devices, but there wasn’t anything in their book that I liked. Rather than make something up from scratch, I decided to work directly from the Holt Physics textbook.
The lab had two parts; the first was to calculate the spring force constant using a Hooke’s Law device. I didn’t have that device, so I created my own by first designing a simple indicator on Solidworks (3D CAD Software) and then printing eight of them in the 3D printer. That worked out great. (I will try to remember to post my Hooke’s device design, you can build them for about $0.25 each.) Unfortunately, it was the only part of the lab that worked out at all.
We were able to use a ring stand, ruler, and indicator to successfully calculate the spring force constant. The second part of the lab was supposed to demonstrate conservation of mechanical energy by bouncing the weight and measuring the high and low point. Quite honestly, it just didn’t make sense. At first it did, but the more I thought about it, the less sense it made.
To begin with, it was nearly impossible to measure the bottom and top of the bounce with any accuracy. It was pure guesswork and the kids were really struggling.
This is a great bunch of kids, I warned them ahead of time that this was the first time using this lab, there might be some hiccups. They were understanding and really tried to make this work, but they were totally frustrated. I told them I would grade the lab on their effort, spring constant results, qualitative analysis, and attempt at explaining the results.
Clearly, I need a much better lab for next year. I was originally thinking of calculating the spring force constant, then determining the weight of an unknown object based on distance the spring stretches. That makes sense for the chapter on oscillations, but not for Conservation of Mechanical Energy. I don’t have an air track, but I’m really good at McGuyvering solutions, as you all well know.
Please throw your awesome labs my way, I need help.