Daily Archives: December 2, 2015

Shopping in a parallel universe

So this is quite fun.

As I’ve mentioned before, my big project for last year and this has been to completely re-write the KS3 SoWs and lesson plans for the whole of Science. I wanted to completely change the emphasis of the subject, from one of students receiving information, writing it down and regurgitating it on demand, to a course based on investigative practical work with as little note taking as possible.

The main challenge for me has been the Physics topics. Biology is obviously not a problem, and Chemistry was my favorite A-level, but I dropped Physics at 14, baffled and frustrated by moments, magnetism and the apparent pointlessness of Hooke’s Law.

But conceptual difficulty for a teacher can be a good thing. If I don’t understand something, I certainly can’t teach it effectively. If I have to go out and learn something new, then it’s much easier for me to understand how and why a student might struggle with it. And it forces me to come up with imaginative solutions.

So one of the topics that the Head of Physics wanted covered was Energy. I did lots of reading for this. The most helpful resources were the Nuffield Physics website which provided lots of excellent ideas for practical work (check out what you can do with a brick!) and Peter Atkin’s superb 4 Laws that Drive the Universe….


which I found absolutely compelling.

So, I put together a course that focused on the idea of Energy as always being in a store, and that to make anything happen, energy has to move from one store to another (Nuffield recommends that you make no mention of types  of energy as this leads to unhelpful confusion). So the students burned wood shavings to compare the quantity of energy in different types of wood and built splendid (and occasionally terrifying) trebuchets to illustrate the idea of energy transfer.

And then there was this idea for a lesson on Entropy.

I started with the traditional idea of comparing Energy to Money. You can keep them both in a “store”. But nothing happens until you move it from one store to another. Plus it’s quantifiable. When they were happy with that, we moved on to the activity.

You need several boxes of maltesers, a paper shredder and wads of pretend money – £100 in £10 notes, and £200 in £20 notes.

Divide the class up. For a class of 20, 5 shopkeepers. Tell them they’re selling boxes of maltesers for the princely sum of £100 a box. They cannot pass over a box until they have the full £100 in their hands.

5 groups of 2 shoppers each. Give them a wad of £100 each. Tell them that their challenge is to buy a box of maltesers.

And 5 intermediates. Make it very clear to everyone that money must pass through the intermediates. So if shoppers want to buy something, they must pass the money to the intermediate who will pass it on to the shopkeeper.

Then take the intermediates somewhere quiet and explain that when the shoppers give them some money, they must put 90% of it into the shredder and only give 10% to the shopkeeper. But they mustn’t tell anyone what they’re going to do!

Then let the game commence.

It is joyous. Excited by the prospect of chocolate, the shoppers eagerly hand over their £100 wad to an intermediate. The look of shock and outrage on their faces when the intermediates calmly shred £90 is utterly priceless. Nobody gets any chocolate. What’s going on?

So I ask them to imagine this weird parallel universe where shopping involves the automatic shredding of 90% of their money. To buy something worth £10, they have to hand over £100. Where’s the other £90? They point – it’s in the shredder! In other words, it’s still in the universe, it hasn’t been used up, it’s just no longer in a usable form.

So I restart the game. This time the shoppers have wads of £200. Can they figure out a stratagem for getting any maltesers? Perhaps they need to think collectively?

Eventually they get it. If they pool their money, they can hand over £1000 to an intermediate and although £900 gets shredded, a shopkeeper will get £100 and the class can all have a malteser each.

But how does this link to energy? I produce some alcohol and ask them to imagine it’s petrol. How do I transfer the energy? It needs to burn. So I pour some into a crucible and light it. If this is a car, I ask, where do I want to move the energy to? The wheels. But feel it! What is happening to most of the energy? They can feel the heat.

For shredded money, read heat. We’re looking at Entropy.

This leads neatly to an exercise in trying to light a fire with a fire drill http://www.jonsbushcraft.com/bowdrill%20tutorial.htm, which generates lots of smoke but, not yet at least, any flames…. But when we go through the various energy transfers and the first concept of some kind of Sankey diagram, it’s quite fun to ask them how they feel. Hot? Well, why would that be….

Last burble of the year next week…..