# Day 9: The Same Problem, Solved Differently

Wednesday, September 19, 2018

Students put a scenario on the whiteboards, then posted them up front once we agreed on the content. In the interest of emphasizing energy flow AND systems with energy coming in from the surroundings, I redefined system boundaries and re-diagrammed the same scenarios above. The picture below shows three problems we worked on during class:

After students diagrammed scenarios, we agreed the student-produced boards were correct. I then showed how shifting the system boundary could change the energy analysis.

To check their ability to manage the flow of energy into or out of a system, I gave them the following problem:

I throw a tennis ball into the air. States are defined as drawn on the whiteboard. Draw LOLOL diagrams (that’s a 3-state LOL diagram) to show the energy shifts throughout. But let’s make it interesting — half the room should include me in the system and half should leave me, the thrower, out of the system.

Another practice scenario — me throwing a ball into the air. Two student-produced boards — one of which leaves me out of the system.