Day 134 – Finishing Momentum

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.

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.

Day 133 – Math 8 is Back!

Math 8 – Today was my first day back with the grade 8’s, with my awesome student teacher, Jenny Yim, finishing last week.  She did a great job.

Today I wanted students to work with titled squares as an alternative to the Pythagorean theorem.  I framed it like this:  “I don’t trust 2500 year old Greek mathematicians.  Especially ones that throw their friends into a lake because they think that there is something called an irrational number.”

Once students are comfortable with using the titled squares I’ll show how it can be used as a proof for the Pythagorean theorem.

Day 130 – Conservation of Momentum

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

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 126 – Oops.

Physics 11 – A couple of oops in the pictures above… First, the dreaded twisted slinky.  This is annoying but I sort of get why it can happen. The quiz however is much harder to understand.  What is it about my teaching which allows even one student to have such little understanding to make the mistakes shown above?  Sometimes teaching can be frustrating. It’s a constant puzzle to figure out what went wrong. I guess this is the intellectual challenge that keeps it interesting.

Day 124 – Bridge Breaking

Engineering Physics – I finally built my bridge testing apparatus.  A bottom beam sits on two bathroom scales.  Another beam slides on threaded rod which is attached to the bottom plate, and by tightening the nuts on the rod, the top beam compresses the bridge truss and bottom beam against the bathroom scales.

The bottom picture shows the bridge truss that withstood the greatest force.  Lots of bridges failed at glue joints which surprised me. I need to look into that for next year.