Day 46 – Gravity and Size of Forces

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Physics 11 – Today was the students’ last day at analyzing gravity. They worked towards the understanding that big objects and small objects exert the same gravitational force on each other.  This will also become a valuable lesson when it is extended to the more general case of all forces and interaction pairs.

Day 44 – Gravity as a Mutual Force

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Physics 11 – Today the classes worked towards whether or not small objects exert a force of gravity on large objects.  The above voting question is where the kids voice their understanding.

Two of my classes worked through this ok but one class really struggled. As a result, I typed out an argument/reasoning for them. I think it may have helped a few students.

Day 28 – Mini Whiteboards and Plickers

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Physics 11 – This year every student of mine has their own Plicker card.  In previous years I kept one laminated set of plickers but it was a bit of a pain to work with.  It took time to hand out and collect, and it was too difficult to ensure that each student had the card number that they were assigned to. What I did this year was combine a plicker with mini whiteboards.  Each student received a plicker card printed on regular A sized paper, one A sized sheet of card stock. These where then slid inside a plastic sheet protector and voila!  Not only do they have a plicker card but they have an erasable surface for questions that involve writing down an answer or graph.  For example, I can ask students to predict the v-t graph of an object’s motion.  I still use Peer Instruction with Plickers and it continues to be a solid system to use.

Day 78: Peer Instruction on Projectiles

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Physics 11 – Today it was time again for more peer instruction. I had gone over the basics of projectiles with the class fairly briefly.  Somewhat different to how projectiles are covered in BC, I delayed introducing them until after we had done unbalanced forces.  At this point students can clearly identify the single force acting on the projectile and how it has constant acceleration downwards, and constant velocity horizontally.  Sequenced like this, projectiles do not have any new concepts in them.

This first question required two votes, but the students had almost 100% correct on the second vote.  The next question I knew would be more difficult:

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The students had only one piece of the puzzle to figure out this question, and a few students picked up on it.  Most did not, even after two votes.  The concept that helps answer this question is that the time a projectile spends in the air depends on the vertical motion. Specifically, the more vertical distance traveled, the longer the time spent in the air.

I’m continuing to use Plickers for peer instruction, and it is working very well.  The software has improved over the past year and the voting appears to be more reliable.

Day 68: Peer Instruction on 3rd Law

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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.

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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.