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Impulse Momentum Brain Dump

November 4, 2017

Curriculum development has moved me in a direction of teaching momentum in following order.

First: impulsive forces 

Investigating impulsive forces–factors that effect peak force and duration. We us force sensors and change factors like mass, speed, bumper stiffness in collisions with a wall.

We then introduce and practice with impulse and change in momentum, both with sensors and logger pro and by hand. Clicker questions, ranking tasks, and a problem to determine the impulse and peak force of a baseball bat on a base ball.

Second: Collisions

Investigating elastic collisions comes first. Doing this helps conceptualize the process as momentum transfer. We start with equal masses. All the momentum is transferred. We then look at cases where some but not all of the momentum is transferred, and finally when more momentum is transferred than one had to begin with. 

After observing and discussing qualitatively, we get quantitative, but I don’t have students predict anything. We observe and analyze it in terms of momentum, for the purpose of determining how much momentum was transferred. We draw before during after diagrams.

At end, we see that the momentum of each system is constant, and I introduce concept of an isolated system We look at explosions next as another example of isolated systems that starts with zero momentum. Students analyze mock explosion data and sort them into possible and impossble explosions. A little bit of neutrino history gets sprinkled in here. 

Finally we look at Inelastic collisions, and this is the first time students use momentum conservation to make predictions. Studnets  predict final velocity, but then must also determine how much momentum was transferred. Doing so involved practice shifting perspective, from system to individual objects.  

Many times people start with Inelastic collisions, but I think that’s a mistake. While you can calculate easily, it obscures transfer. Elastic better promotes transfer idea I think.


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