Day 134 – Finishing Momentum

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Physics 11 – We did a bit more practice with conservation of momentum today, along with some Peer Instruction voting.  To help with one question, I fired up the good old air track, shown in the video above.  The air-track is good but it’s limited by the carts that I have for it and the lack of a good spring plunger.

One of today’s voting questions is below.  I keep forgetting that this is pretty tricky for physics 11.  On the one hand the correct answer is intuitive.  You load something up with more mass it will slow down.  Using the concept of total momentum being conserved is harder though because students want to know what happens to the momentum of the rain falling.

cart-rain

I briefly talk about how momentum is a vector and we have to consider that momentum that are perpendicular do not add together as a single number.  I then quickly try to change the topic as this is waaaay above where we’re at with the topic.

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Day 130 – Conservation of Momentum

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Physics 11 – We finally finished the video lab, after 2.5 days on it. Whew.  I’m afraid we don’t have much to show for it.  A few students had some insightful thoughts on what they observed but really it was too little for too much time spent. I blogged much more about it on my edblog.

One student was able to claim that it seems as though the momentum is transferring from one object to the other, which was a great thought. Another student reasoned that momentum should be conserved since Newton’s Third Law tells us that the forces are the same but in different direction, which means that whatever momentum one object gains, the other must lose.

Day 128 – Momentum Video Lab

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mom lab

Physics 11 – This is the lab I settled on for conservation of momentum.  Students will use three Direct Measurement videos (dart into cart; Hailey and Connor; Hailey, Connor and Christine) and three videos that they will record themselves of two carts on an air track (head on collision, collision in same direction, collision into a cart at rest).  I thought about giving them an Excel spreadsheet for entering in their data, but that would make the experiment very much a “black box”.  The amount of time this lab is taking is concerning though.

Day 122 – Whiteboarding CoM

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Physics 11 – Whiteboarding last day’s results was the main even for today but I forgot to take pictures.  By going around the room from whiteboard to whiteboard I posed the question, “what pattern do you see?”  Inevitably the students start to see that in each case, the moment of the objects before the interaction is equal to the momentum of the objects afterwards.  Ah ha! Conservation of Momentum!

I then showed the students how conservation of momentum can also be seen as a consequence from Newton’s Third Law.

 

Day 120 – DMV Conservation of Momentum

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Physics 11 – Students used a variety of impulse/collision Direct Measurement Videos today. The goal was to collect data and analyze the total momentum of the objects in the video (system).

A couple of groups got a bit confused because there was missing information on the videos (these videos work towards using conservation of momentum to solve for unknowns). I may need to re-jig how I delegate videos to the groups next year.

Overall the DMV are a quasi-reasonable substitution for not having appropriate lab equipment.