Physics: The Qualitative Second Law Lab

This is a follow-up to my previous post about adjusting my Newton's Second Law warm-up investigation to an almost purely qualitative experience.  (Remember, my physics course targets those lacking analytical/mathematical confidence.)  Basically, I used to do a more complicated lab involving an Atwood machine and a motion detector and have the students plot how acceleration changes with mass and with net force.  Every time I've attempted this type of lab, no matter how scaffolded and no matter how many velocity vs time graphs we practiced in the previous unit, the students would get tremendously anxious about the math and not be able to draw conclusions.  They simply froze.  I've actually never had a student come up with the second law after the lab...which is super sad since that is the ultimate goal.

A few weeks ago, I did this lab qualitatively for the first time in all four sections.  Here are the images of the lab so you don't have to scroll on the older post...
qualitative newton's second law lab DiSanto physics page 1
qualitative newton's second law lab DiSanto physics page 2
Here's how the class went:
  1. First, the students wrapped up some Fnet practice on the whiteboards (drawing force vector addition diagrams and determining the magnitude and direction of the net force). Basically, they did three problems producing work similar to what is shown below.  The velocity vs time graph at this stage was qualitative only since the students didn't yet know how to relate a velocity vs. time graph to a force vector addition diagram (2nd law!).
    disanto physics force vector addition diagram sample
    I did this first to remind them what total force was since we had been so focused on balanced forces in previous units.
  2. As they finished whiteboarding and were reading the instructions for the lab in their Unbalanced forces packets, I dropped off a ramp, fan cart, and extra masses to each table.  One person from each group went to grab a phone from our cell phone spot for timing.
  3. They worked through the lab on their whiteboards with little to no questions.  I did this four times as I have four sections and, other than groups that need universal encouragement, the students were able to work through it all without intervention.  This is a pretty big deal, to be honest.  Hands-on experiences so often lead to debilitating nervousness (amygdala hijacking as we've been learning in our PD sessions).  But not this time!
  4. I had MULTIPLE groups come up with second law on their own.  Happy sigh...  Did everyone come up with it? No.  But everyone made it through the lab and could explain how acceleration was impacted by changing mass and changing force.  Win.
What do I want to do next time?
  • The lab was super fast...20 minutes on average.  I want to add the calculation of acceleration back in with the velocity vs time graphs.  Some groups started doing this on their own which was awesome.  This does bring me back into the analysis zone, but I think I can incorporate it in a low-stress kind of way.
  • I want to possibly have the members of the groups that DO come up with second law help other groups get there too instead of me.


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