POMs-The currency of momentum
We’re studing momentum in my honors physics class, and I’m thinking back to all the fun we had last year designing a completely new unit for momentum, the Parcel of Momentum (POM).
I’ve spent the past few days trying to follow Kelly O’Shea’s great introduction to the Momentum Transfer Model (MTM) paradigm lab, but we had considerably more trouble than her class did. Ultimately, we got to the point where we were looking at a data table that looked something like this:
And we began to study this data looking for a pattern. Eventually, some students started to see that in some cases, the changes in velocity were exactly opposite one another, and these cases happened to be when the masses were equal. Later, they realized that in cases where the changes in velocity were not the same, the more massive cart had a smaller change in velocity than the less massive cart. And from there, students were able produce a nice graph showing that , that the carts seemed to be swapping something during collisions.
One student even said that it was like two people swapping money, and so this got me thinking, and I designed this with a little bit of free time today:
So now I have a momentum currency for my class, and for a few minutes, I thought this would be cool for some sort of demo/activity in class. I’d give everyone a set amount of money, and then we’d simulate collisions where they would “transfer” momentum currency to one another. Finally, we’d tally all the individual transfers and see that momentum is conserved.
But then I got to thinking about this a bit more, and I’m not so sure this is a wise way to go. There are lots of ways that my momentum currency may confuse things more than I want. First, momentum is a vector, without creating some sort of perpendicular currency, I’m not sure that they will get that having more momentum doesn’t mean you can move in any direction you want. Second, objects end up with negative momentum, meaning they’re traveling in the negative direction. However, I have no way to track negative momentum, and so it would seem that this currency idea might mistakenly make students start to treat it like a scalar quantity, rather than a vector. Finally, I use the money metaphor a lot when dealing with energy, so I’m not sure we need a currency for both momentum and energy, and think that could get confusing fast.
So now I’m tempted to keep my POMs for myself, and not doing anything with them. But I’m curious if you have any suggestions about the usefulness of this activity or how to improve it.