Egg Drop

We answered some conceptual questions about impulse and momentum from the packet and whiteboarded them last class.  Then today we did one impulse problem for practice and did the Egg Drop Challenge.  I got this from the IIHS “Car Crashes:  It’s Basic Physics” video packet that I helped with many, many years ago.  teachers_guidePhysics(2)

The kids were given 10 sheets of paper and 1 m of tape, and had to build a landing pad for an egg, dropped at various heights.  This was really fun, and I was very pleased that one of the best designs used paper folded as accordions to increase the stopping time!  Many kids completed missed hitting the device when they dropped, which was funny!

Egg Drop Egg Drop Egg Drop Egg Drop Egg Drop

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Egg Drop

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Day 96: Whiteboarding

Today AP Physics 2 students prepared and presented whiteboards covering a variety of motional emf and electromagnetic induction problems. Many of these required many problem solving steps and integration of concepts we have previously studied. This student ended up being the only one in his group and, on his own, prepared a very clear and concise solution:

Day 96: Whiteboarding

Another group made a couple of mistakes and found that the temperature of a muscle during an MRI would increase by 80°C! They weren’t nearly as concerned about this result as I was!

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Day 95: Peer Instruction for Electromagnetic Induction

Today, we spent the entire class period doing peer instruction for electromagnetic induction questions. Properly applying the right-hand rules, Lenz’s Law, and constructing the long chains of reasoning necessary to answer these questions requires a lot of practice. The cumulating question was the following from Knight’s College Physics:

Day 95: Peer Instruction for Electromagnetic Induction

Initially students really struggled to capture this relationship. Only one student sketched the correct graph. Most sketched something along these lines:

Day 95: Peer Instruction for Electromagnetic Induction

After some guiding questions from me and discussions with their peers, several groups produced the proper sketch:

Day 95: Peer Instruction for Electromagnetic Induction

Definitely one of the more challenging questions we’ve discussed!

&nbsp ##magnetism ##peerinstruction  

Force and Time

We put finishing touches on the lab today, and then began a discussion on J = Ft…  mainly that when the change in momentum is the same, the impulse is the same.  Increasing the time then lessens the force, and vice versa.  I have always used the water balloon toss as an example of this (how you sort of catch it with some “give”) – and this year I thought – why don’t we just do it??  No idea why I never did it before!  Super fun, and I am sure they will remember!  After this activity and discussion, we watched this video  https://www.youtube.com/watch?v=qSydxQWjj4I   in prep to do Challenge 1 (looking at some car crash videos and thinking conceptually about changes in force and time).  Success!

Force and Time

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Force and Time

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Developing Impulse

OK this lab came out way better than I anticipated!  The results were pretty consistent, minus a group or so from each class…  Here is what we got.

1.  The longer the tube, the further the marshmallow travels.

2.  The harder you blow, the further the marshmallow travels.

3.  The higher the mass of the marshmallow, the less far it travels.

4.  The higher the marshmallow is shot from, the further it travels.

The first three were BRILLIANT in explaining J = delta p.  First we WB the results and did a gallery walk, where they checked all results to see how they compared as a class.  We talked first and developed the equation Ft = delta (mv) as we went….

We discussed variable by variable what we got and WHY.  They intuitively could see that if you blow harder, the mallow should go faster as it leaves the tube (and therefore farther).  The “F” part of the equation increasing, therefore increasing the “v” part (all else was held constant).

When the tube is longer, they said it was in there getting the force for longer…  so the “t” part of the equation increasing, thus again increasing the “v” part. (all else held constant)

When the mallow was more massive, it did not go as far.  Again, they sort of intuitively know this even though we have not done F = ma yet.  Same blow force and same tube length means the Ft part of equation is same in all trials.  So when the “m” is bigger, the “v” is smaller, meaning the mallow does not go as far.  Brilliant.

Lastly, changing the height did not affect anything in the tube, same F, t and m will make for same “v” each trial….  but yet the mallow goes farther when starting higher.  No study of projectiles, but through some drawings they could see that the time to fall is more, so the mallow has more time to move before hitting the ground, getting further.

The reports I have glanced at look really great.  I am really proud of them!  A great experiment for learning the concepts as well as designing an experiment (esp. in controlling variables!).  LOVE THIS!!!

Developing Impulse Developing Impulse Developing Impulse Developing Impulse Developing Impulse

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Developing Impulse