Day 93 – Projectile Crime Scenes

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Physics 11 – I pulled out an activity that I haven’t used for a few years, the ol’ Projectile Crime Scene.  Students are given one of three crime scenes to investigate.  Above you see the Hotel Jumper, where students use a scaled model/drawing of the hotel and where he landed.  The idea is that they will use the height to find fall time, and then horizontal distance and time to find the horizontal speed. From this, they use data tables on men walking and running speed to see if the man was pushed out of the window or if he ran and jumped in an attempt to land in a pool below.

The other two activities are very similar, they all involve a horizontal launch projectile where students need to find a horizontal speed.  These are engaging tasks but also very difficult because of the extra cognitive load placed on the students.  In the hotel jumper, the students need to deal with a scaled model.  In the Gangster Shooting, the problem involves a bit of math and reasoning to make a proper sketch of the crime scene. Road Rage involves some kinematics and acceleration prior to the projectile part.

Despite the difficulties, I believe it’s a good task to do. Perhaps it would be better if more practice was spent on projectiles. Or, despite it being a horizontal launch problem, it might be better suited to Physics 12.

Day 89 – Projectiles

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Physics 11 – One of the best things I have changed in physics is the order in which I do projectiles. From what I’ve seen across Vancouver, most teachers do projectiles at the end of kinematics. However, I now have students learn about them after we’ve done forces. At this point the students are about as good at drawing force diagrams and recognizing balanced forces as they will ever be. Therefore, the students in general have no problem understanding why a projectile only accelerates towards the Earth but not horizontally. They also have done some vector analysis with force diagrams, so the idea of vertical/horizontal components is not a new concept.

This is not to say that projectiles are easy for students. These questions often involve multiple small steps for solving and while the students can do each small step individually, putting them together into a complete solution is challenging. As well, this is a topic that only motivated students seem to do well in. I don’t have students hand in homework, so if they slack off, then the chances of them being successful is not that great.

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.