Dot Physics

What makes a good lab?

I was wondering around the blogosphere and read some stuff about introductory physics labs. In particular, I was looking at ZapperZ’s Revamping Introductory Physics and Dr. Pion’s Objectives for a Lab. Both of these are good posts. Here I thought I would add make take on this subject as I am picking the labs I will use for the summer session of introductory (algebra-based) physics labs.

When I first started teaching this lab, my goals for the course were a lot like Dr. Pions. Namely, I would like the students to improve in the following areas:

  • Critical thinking
  • Writing and communication
  • Data analysis, measurement and uncertainty
  • Experimental design
  • Understanding the nature of science
  • Numerical calculations
  • Conceptual physics
  • Reading and following procedures
  • Using tools – like spreadsheets and video analysis

Yep. That is a lot of stuff to cover. When I first started teaching labs, my main focus was on the writing aspect. My plan was to use a peer ranking system. In this system, students would anonymously rank other students reports. The idea is that students that are good at writing should be good at ranking. This could also be used as a way to reduce the grading from the instructor. Another benefit is that students could possibly learn from other students’ mistakes. The students might be more careful about spelling and stuff if other students were going to read it.

I never really got the peer ranking thing working too well, and I realized that I was trying to do too much. Really, you have to pick one battle that you want to fight in that lab, maybe you can have a secondary battle also. My too favorite areas to focus on now are data analysis and conceptual understanding. This means that I don’t focus on lab reports so much. Don’t get me wrong, I still think they are very important, but I can’t do everything.

So, what makes a good lab? Well, ideally, every lab would have students collect some data and build a model from that. As pointed out in the other blogs, the problem is that sometimes students already know the answer (like building a model for friction). For me, this is ok sometimes as they still get experience working with data and maybe they can build up some confidence.

How about I describe some of my favorite labs (for algebra-based labs)?

Mass of a penny

This is an oldie but a goodie. Well, it’s an oldie where I come from. Basically, you get a whole bunch of pennies. Find the mass as a function of year. Are older pennies heavier because of all the grime they build up or are they lighter because of wear? This is a great lab to practice measurement and uncertainty and graphing. Of course many of you already know the trick here. The composition of the penny changed in 1984 (I think that is the year). The jump in mass should be significantly greater than the error bars for the data.

Free falling objects

We have these little electronic drop timers. A timer starts when a metal ball leaves the holder and stops when it hits a drop pad. Pretty simple device. I like this lab mainly because it is simple. No computers needed (computers can surprisingly bring lots of trouble – maybe not so surprisingly). Students measure the time for different height drops. They also explore if mass has an effect on free fall acceleration. This is a great lab because it helps them understand the purpose of a graph (many students think the purpose of a graph is a graph). If students like, they can do this graph on normal graph paper. I encourage them to do this by hand.

Falling coffee filters

Another classic. In this lab, students drop stacked coffee filters over a motion detector (like the Pasco or Vernier detectors). The cool thing is that by stacking the filters, you can change the mass without really changing the air resistance. This is a great lab in that they students can’t really calculate this motion analytically, but they can do it numerically (I have them practice numerical calculations on just about every lab).

Springs

Here the students calculate the spring constant of a spring. They do this by stretching it as well as by making it oscillate. The idea is simple enough that students can design their own setup. Also, this is another one that can be modeled numerically. If you are evil, you can have the make the spring oscillate with a mass smaller than the mass of the spring. In this case you DON’T get simple harmonic motion (Mu Ha Ha Ha HA). Clever students might be able to come up with a way to model this by representing the massive spring as a series of springs with masses in between.

Comments

  1. #1 Uncle Al
    May 25, 2009

    When a stretched Slinky is driven to successively greater transverse oscillation frequencies, is it a dispersive medium?

  2. #2 Al
    May 25, 2009

    I do most of these labs with my students too. When I started teaching, I was surprised to learn that students couldn’t take the data-analyzing skills they acquired in 1 lab and apply them to other situations. Now, I often build a lab with experimental error and the students have difficulty coping with the answer they get being so far from the ‘right one’ such as calculating h from the voltage drop across LEDs.

  3. #3 Dave
    May 27, 2009

    Make sure you include some 1943 pennies in your Penny Experiment. ;-)

    For the Falling Coffee Filter Experiment, make sure you have a large fan running in the lab. ;-)

    For the Free Falling Object, make sure one of the tests is with a magnetic object and a Copper pipe it’s falling through. ;-)

    Dave

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