Day 68: Peer Instruction on 3rd Law

3law1

Physics 11 – Having discussed and debated about Newton’s 3rd Law last day, today was a chance to put the students on the hot seat with Peer Instruction.  Class #1: first vote was about 70% correct, moving to everyone correct but one person on the second vote.  Class #2: first vote had over 80% correct, no second vote required.

3law2

This question was more difficult because the answer is more subtle.  Class #1: first vote was about 60% correct, moving to 75% correct on the second vote.  Class #2: first vote was about 60% correct moving to 90% incorrect on the second vote.

I could see how students were convincing with their incorrect arguments.  The key was in the drawing of a force diagram, but very few students wanted to do this.  However, as time moves on I think I am slowing convincing students just how important a force diagram is.  Now that we are doing more word problems (5e: extend), I am reinforcing the idea that physics covers the force diagram and writing an equation for the net force, and then the rest of the solution is math.  By skipping over force diagrams, the students are not demonstrating understanding of physics.

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