School starts at Culver Academies tomorrow morning. I will be teaching conceptual physics for the first semester, generally a group of students who have just recently taken chemistry and have had biology their freshman year in school. As a department, we have been changing things around, with a new focus on physics as a foundational topic leading into chemistry, which then provides a backdrop for understanding the complex chemical processes involved in biological processes their junior year. Another focal point for the department has been on developing and fostering inquiry centric activities within the classroom. In physics, we have been doing quite a bit of this, replacing traditional lectures with POGIL group activities, and with the development of spiraled inquiry units (see my last post on the LED unit). So I thought now is as good of a time as any to re-evaluate my opening lab activity that I will do with my new students. The goal is always to get students to show (indirectly) how they percieve the “doing” of science, in the context of investigating precision in simple lab measurements. We do this by asking them to attack the following list of tasks:

At the beginning of class, students will be broken up into groups of 3-4 and we will spend a few minutes discussing the goals of the lab. After the brief introduction, they are free to develop and implement experimental procedures to gather appropriate data for each task. Now this is where I am a bit tricky; around the room are three digital balances, one which reads to the nearest gram, the next to the nearest tenth of a gram, and finally a balance which reads to the nearest hundreth of a gram. I make a point not to mention this, aside from encouraging groups to think carefully and document the equipment they use, and why they chose to use that particular piece of equipment. Likewise, I give them multiple rulers to make linear measurements, and different glassware for volume measurements.

Many students think these two rulers are the same.

A rather big change this year was task 3. The goal here is to get students to realize that if they are to determine the area of the irregular piece of paper, they will need multiple data points of a measureable quantity (in their case they can only determine the mass directly of the irregular piece). The hope is that they will collectively realize that the regular square, rectangular and triangular pieces of paper are of utmost necessity to generate a Mass v. Area plot, a concept which was frequently used in their chemistry classes when identifying glasses based upon density plots. We’ll see how this one goes…

Sample pieces of card stock used by students in task 3.

All in all, this lab activity provides tremendous insight into the problem solving abilities of students, as well as giving me a view of their internal definition of what it means to be precise in making measurements. I don’t make students do a traditional lab report, instead opting for a group presentation based upon some analysis prompts that I provide in the student handout. I can’t tell you how many groups will do single trials of one drop of water and report that the drop had no mass, only because the balance was not sensitive enough. It is these types of roadblocks that I want them to get used to breaking down together.

If you are interested in the activity, please feel free to download a copy:

Conceptual Physics Lab 00A: Precision, Measurement & Accuracy

I’d love to see how you approach the first lab activity of the year in your science course, so please share!

Hi Phillip:

Back in day when precision and sig figs where a Big Deal in my class, I asked my students to determine the interior volume of cup using 3 different methods. After some class discussion, the kids came up with: (1) measuring dimensions and using the volume formula; (2) filling the cup with water and pouring it into a graduated cylinder or beaker; (3) filling the cup with water, finding the mass of just the water inside the cup, and using the density of water as 1 g/cc to calculate volume. They were to compare their own answers to see which method was most precise and most accurate. I like the multiple methods aspect because in physics there is usually more than one way to approach a complex problem.

Also, I think for your area of an irregular shape problem, I would just mass the largest piece of paper available, find its area, and set up a proportion. No graphing necessary. The smaller the piece of paper, the larger the relative error associated with the measurements, which would then be introduced into the graph.

Students may very well gravitate towards setting up a proportion, but it will be interesting to see if they trust a single measurement (which they should not) and be willing to base their conclusions upon that singular data set. Sig figs are not a big deal but to me are important in that students must be able to record measurements appropriately. Overall, the lab is a good window into the problem solving methodology of incoming students.