Day 94: The Start of EnergyPosted: February 10, 2013
I started the energy unit today (ok, thursday) in physics. I used a modification that Kelly recommended of her own ETM paradigm demonstration . This is a really cool way to get them thinking about the physical meaning of graphs, particularly that which we haven’t looked at for a while, area. The idea is that we are going to launch these identical in mass carts with two different springs. How can we get the same speed at the end? I gave them a graph of each spring’s F vs. dx graph, thanks to my colleague Ben.
It is obvious to students that pulling back the same distance won’t work. How about the same force? It’s pretty cool that pulling back to the same force value actually causes the weaker spring cart to go faster; same average force means same average acceleration, but that average is occurring over a larger distance and thus for more time, thus that cart speeds up more.
Then I tried to lead them to using area. We have room to improve on getting students to use area of v vs. t graphs to solve kinematics problems, so it was difficult to get them to think of using area. We got through the calculations (they have a hard time with choosing an arbitrary starting point for one spring and using that to find where the other one should be pulled to), and went back to test the spring displacements we have calculated. They are spot on for getting the carts to move at the same speed, which is pretty cool.
Now, I really like this. However, I don’t like that (at least in how we have planned Energy from here on out) we leave the area piece alone for a while as we build the idea of energy transformation and conservation. I’m thinking pretty seriously about modifying the start of the unit to play off the idea that the area under the F vs dx graph gives the change in energy, which I hope to explore in CIS (advanced, college level) physics. I have some ideas but need to flesh them out, I’ll probably be posting them soonish.