Motivating Equations In Physics
Equations in physics help us to solve problems, but this isn’t immediately obvious to students. I try to motivate the utility of equations in my lessons by following a similar method for each equation. Here, I’ll use the example of calculating the work done when pushing an object. A lot of the inspiration for this comes from Gethyn Jones article in Impact on p-prims – how you go about priming the students to appreciate whether relationships are proportional or inversely proportional or something else. I want students to “see the physics” and then use their knowledge to feel confident in performing calculations, appreciating why they’re useful and how they relate to the underlying physics concept.
I start by drawing out a situation that is typically a comparison between two different scenarios (cue award winning drawing)
As I draw this out, I’ll explain what’s happening and often set this is as a ludicrous comparison between myself and the neighbouring science teacher (or student in the front row). I then add in ‘the numbers’ to allow students to compare.
So the process starts with a very concrete example, with the underlying concept being made even more concrete through the comparison of the two, different situations.
I very purposely keep one thing the same and change only one variable. I won’t explicitly calculate work done, but we’ll discuss that the top person (yes, that’s me with the glasses) has done more work because they’ve had to use more force.
I’ll then set up a second scenario where I change the other variable (and keep the first one the same)
Again we’ll discuss that more work is done in the second scenario as they’ve exerted the force over a long distance.
We will probably stop now for some basic questions to clarify this relationship “as force increases, more work is done” etc. We might do some other simple comparisons and use whiteboards to check that they can easily see when more work is done in scenarios where only one variable is different.
Students are now good at saying “more work is done in scenario A because…” Now I motivate the use of equations by giving a comparison like this
Students can’t immediately see the correct answer, so to work out who does more work, we are forced to do a calculation. Some students are very good at deducing answers though here which shows that they’re thinking about the relationship e.g. “the force in A is more than half of B, and the distance is more than double, so it’s A” – I’ve got no problem with this. I point out that writing that down takes longer than doing the two calculations (but it’s a great example of thinking like a physicist and throw a load of praise their way). You can tailor the numbers in the example to make this as easy or as hard as you need.
Harry Fletcher Wood discusses student motivation in his book Habits Of Success and on various podcasts and gives the example of being an aspirin salesperson. The perfect customer to sell aspirin to is someone with a mild headache – people won’t appreciate the aspirin if they don’t need it and you ethically shouldn’t force it down them. Aspirin here is “using a formula to perform a calculation” and I’ve created to headache by ensuring there’s no direct comparison between the two scenarios. Students should now (theoretically) come flocking to me for the solution – and they certainly do find this much more satisfying.
This brings up the notion that maybe you could start with the final example instead, as this is the headache. But students would not have built up an appreciation of the underlying physics concept without those simpler, less headache-inducing examples.
If you’d like to read more about teaching through examples see my previous post. Let me know on Twitter (@tchillimamp) how you motivate equations in your lessons.
