# Day 11: More Energy Transfers

“On a group whiteboard, draw an Energy vs. Time graph for the cart

hitting the rubberband. Include:

(1) A graph for Ecart

(2) A graph for Erubberband

(3) A graph for Ecart + Erubberband

Start your graph from BEFORE the push (initially at rest).

End your graph when the cart is moving full speed in the opposite direction.”

Again, we haven’t talked about what energy means or the different

“flavors” of energy. I just wanted to see what notions the kids had

about this system. There was some interesting discussion as to whether

the rubber band started with some energy before the cart even hit it.

Other things:

** By including the push in the graph, we can talk about open/closed

systems and when energy is conserved.

** I like begining with focusing on where the energy is (in terms of

the objects) rather than the flavors of energy (kinetic, elastic,

etc). Kinda reminds me about whether we label forces like Fg or

Fearth. I think starting with objects lends some concreteness to it.