We're back after another day off, this time for Yom Kippur. It's hard to get into my teaching groove this week, especially with the shorter classes, so again with no picture today.

We worked on a few problems today. Many students instinctively started by drawing interaction diagrams and LOL diagrams, and these are the students who had the most success. I'm not sure if some of them saw the connection. Even though we drew diagram for twelve problems before it, if I don't ask for a diagram, they don't want to draw it. Some of them don't get the point of the diagrams yet. I gotta work on that.

We talked about the difference between work and pseudowork in class today. Work is when energy enters or leaves a system, and we can calculate that through the area of the force-position graph. Pseudowork is when energy transforms into thermal energy, some staying in the system and some leaving the system. We calculate it using the area of the force of friction vs. position graph, but while it looks like work, it isn't work. Not all that energy leaves the system.

Did a tiny bit on power today by having a short student and a tall student try to lift a heavy backpack 2.0 meters off the ground. They did the same work, but something was different. We called that difference power, and it's measured in watts. (What?)