Center of Mass Lab

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So, we’ve now had some discussions based on our center of mass lab (my last post has the set up).  Their boards ended up looking like this:

First, I have to say that these kids continue to impress me with what they are capable of.  Their boards looked great! (well ok some are better than others) Our discussion, on the other hand, did not go completely as planned (although I think they still learned a lot).  Here’s why I don’t think it went as well as it could have:

1.) I didn’t set them up with the right questions ahead of time.  I should’ve had this on the board before we even started talking about results:

2.) I tried to start with a whole group discussion.  Worst. Idea. Ever.  Everyone was afraid to talk because they had the whole class watching them.  They needed to get some ideas first in smaller groups then move to whole class.  Next time, I plan to have each group pair up with one other group and discuss the questions first (actually I already implemented this in one class and it worked way better!).

3.) I didn’t plan the lab set up as well as I should have.  Each group got a meter stick of a certain mass and a metal object of a certain mass. My thinking was that I should just make it random and they would still get the results they needed.  While they did get good results, the discussion suffered because of the randomness.  I needed pairs of boards with specific results (like same slope, different y-intercept) to facilitate discussions.  Next time, I will plan my materials for each group based on how I want the discussions to go.

4.) This one is so embarrassing!  But I didn’t really have a good understanding of where we were going with this lab.  I do now (thanks to another modeler at my school who is helping me out), but at the start of the lab I did not.  I think that’s why I made the mistakes I’ve listed above.  I knew we were investigating the relationship between the position of the object on the ruler and the center of mass of the ruler-object system, but I didn’t know exactly what we were doing with that data.  I think I was going into it thinking we were just going to come up with the fact that the data is linear and talk about the meanings of the slope and the y-intercept (questions 1 and 2 above).  But the real discoveries come from the other two questions (about why the slope and y-intercept are what they are).  I needed to be ready to lead them to discover:

1.) that the slope of the data comes from the mass of the object vs the mass of the system

and

2.) that the y-intercept comes from the ratio of the mass of the object to the mass of the ruler.

Looking back, I’m like “what were you thinking?! you were goin in blind you fool!”.  But that’s the main reason I’m writing this blog, to reflect on my mistakes so that I can improve the next time I do it.  I see now that most of my problems with the lab and discussion came from a lack of understanding of the end results.  So next time, I’ll work backwards and plan the lab only after I’ve decided where we’re going with the discussion.  It sounds so obvious to me now as I type it (duh, don’t you backwards plan everything?).

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2 thoughts on “Center of Mass Lab

  1. This flying blind thing seems completely crazy, doesn’t it ? The kids don’t seem to notice- at least, they don’t seem to be nervous about it. I tell them, I don’t know where we’re going, but it’ll be okay. We’ll teach you stuff you need to know. At first i got a lot of whiners ( this isn’t math, why are we learning this, who cares), but I think they’ve been home and shown their parents what they can do, and they are showing their peers, who are not in our class, what they can do. And I am learning,for sure.
    If you plan the discussion, you’ll just find out that it doesn’t go where you thought. Just go with where it goes, and be okay that you taught someone something 🙂

    • It definitely seems crazy! My kids have been pretty nervous when it comes to presenting or even just discussions, but I think they’re getting used to it. They know they have to participate, no getting out of this one!

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