How we teach energy

I’ve written about what the literature says about “teaching energy” and curriculum. But as we teachers know so well, articles and ideas from non-teachers have to be interpreted, tried out and refined before they are useful in the classroom. So what do our school’s “energy” units look like in real life? (I say “we” because my school have embraced this change, and as far as I can tell are enjoying teaching energy in this way).

I personally don’t see the idea of energy conservation as important for everyday citizens to know about (we are trying to convince the public that non renewable energy will be “used up”, we dont need to confuse them with “energy can never be destroyed…”). But the new NCEA creators have decided that energy conservation is a “big idea”. So how do we teach it?

Year 9 Science

Unit Outcomes:

  • Students can identify energy types (eg. kinetic, gravitational, chemical)
  • Students can show conservation using energy bar charts
  • Students can calculate energy efficiencies
  • Students explore renewable and non renewable energy resources

Yr 11 Science

Unit Outcomes:

  • Students can identify energy types (eg. kinetic, gravitational, chemical)
  • Students can show conservation using energy bar charts
  • Students can calculate KE, GPE.
  • Students can calculate and explain power
  • Students can calculate work

Yr 12 Physics

Unit Outcomes:

  • Students can identify energy types (eg. kinetic, gravitational, chemical)
  • Students can show conservation using energy bar charts
  • Students can identify systems and use the concept of work to account for accounting discrepancies on energy bar charts
  • Students can calculate KE, GPE and EPE
  • Students can calculate and explain power
  • Students can explain when it is more appropriate to use an energy conservation model to solve a problem, than say a forces model, or a kinematics model. (This is the definition of expertise, so really hard!)

Energy Bar Charts

The different idea in how we teach energy, vs how most other NZ teachers teach it is the use of energy bar charts. I do a good introduction to energy bar charts, and a number of examples with the talk I put together for SciCon last year. The rest of this post, I skim over ideas that I illustrate in the video with examples, so its worth watching at some point.

At Year 9, we dont worry too much about defining the system. In essence we chose “everything” to be the system. The key is, we are looking to teach that energy is conserved, and this is shown with the same amount of energy “bars” on each side of the diagram (even if the energy is in a different form).

You make think this is so obvious, and doesn’t need to be taught with this diagrammatic method, but I can assure you, to the students, energy conservation is not obvious. This method has two great advantages:

  • It makes energy conservation (an abstract idea) visible to students.
  • It makes the student’s understanding (or misunderstanding) visible to teachers.

And so we practice many of these situations.

  • Here is a Phet Simulation we use (Skate Park)
  • Here is a video of a classroom whiteboard session I basically copy (I am a huge fan of using whiteboards with diagrams).
  • Here is a great interactive website where students watch a short video, then have to make the correct energy bar chart. Note: for year 9s using this website, always chose the system to be “everything”. This will become apparent as I talk about “work”. This website was created by Matt Blackman, who is a collaborator of Eugenia Etkina (a big name in physics education research).

Energy Equations

At Year 11 we introduce equations for calculating energy, including kinetic energy, gravitational energy, power and work. But I always do equations in conjunction with the energy bar chart. I don’t want my kids just to be formula hunting. Always, the point is to understand conservation of energy. We teach the formula for work because it will be examined in the NCEA L1 Science exam. However, I believe it should be left out of the curriculum at this level (take note RAS/SEG group!).

Work

Based on what is examined in NZ, it seems that the point of teaching “work” is so that students can use the formula W=Fd. Ask most science teachers to explain the concept of work, and they will give a similar explanation – the formula. I myself would have agreed a few years ago.

Only after using these energy bar charts, and taking time to define systems, have I finally understood the true meaning of work. Its energy that is transferred in or out of a system. Yes, I already memorized that definition, but only through practicing with energy bar charts could I explain when it would be appropriate to use or not use the concept of work to explain a physical situation (say throwing up a ball).

I cannot stress enough how students (and myself!) finally understood the concept of work after doing a number of problems using energy bar charts. Because the “system” and work idea are abstract, I feel they belong in Level 2 Physics, not in Level 1 Science.

Summary

This has been a very useful change to how I teach energy. As I said in my video above, when we teach energy using equations, this overloads a student’s cognitive capacity, and they often miss the conceptual understanding (of conservation of energy). Using energy bar charts focuses just on the concept of energy conservation without being overloaded with equations.

I have said it before: because this is not examinable in NZ, it is always very hard to convince other teachers that the cost/benefit ratio for trying this new idea is worth it. It would be great to see energy bar charts mentioned in NCEA or curriculum documents, but I am not holding my breath. A more realistic dream would be to see some of the NZ science textbook writers pick up these energy bar charts and incorporate them into their books/online courses. Drop me a line if you want some ideas!

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