How I Teach… Work & Energy (part 2)

This is part of a series!
Part 1 (Work) Part 3 (problem solving) Part 4 (Lab)

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We move into energy conservation pretty quickly. Similar to our introduction to work, I pull on prior student knowledge. How many energy forms can you name? As students list them I copy them on the board, sorting them into mechanical and non-mechanical forms. Once we’ve exhausted this list I give them the category names and also the definitions of potential energy as energy of position and kinetic as energy of motion. We discuss how potential energy requires a position that can be measured within the system.

One of the best ways I’ve learned to support students is to teach them to create bar charts. I’ve seen many iterations of this, in the modeling community these are LOL charts. I, personally, haven’t been convinced to continue to use quite as much time on the systems part as many in the modeling community do (literally for the sake of time) but the key feature here is that we are taking concepts and translating them into a kind of visual, mathematical model.

So this is what we do first. We do a few examples (it’s like a checklist!) and then students are on their own for some samples. Emphasis is placed on the process:

1. Identify your initital and final states
2. Sketch a picture of each state
3. Identify your system
4. Identify which energy/ies are present
5. If there is a change between initial and final then we need to include work.
6. Double check that you have, in fact, accounted for any possible external forces that may have done work.

I show students how defining different systems can still get you to the same answer and WOW! Work done by gravity is the same as the potential energy due to gravity… the difference is the system.

I actually have the COVID-lecture version of this video when I wasn’t able to run this lesson with the whole class. While you’ll notice I do go into the math here, it’s really not an emphasis until later. In my regular class I don’t touch it at all until the next day