We worked on energy bar charts today. This year, I'm trying to make the interaction diagram to be useful no matter the model in mechanics we are working on. So I've turned the system O in the middle as a full-fledged interaction diagram. We've even written on the interaction diagram where the energy is being stored. Kinetic energy is just stored in the object; potential energies are stored in the interaction. Work then naturally makes sense as when energy enters or exits the system. We had a hard time decided where dissipated energy is in the friction interaction or floating outside, but we didn't want to put it with Ek, Eg, or Eel because it seemed like a different kind of energy--it wasn't mechanical energy.