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Teaching Energy – The New Approach
Teaching Energy the ‘new way ‘ with stores emptying and filling via pathways has caused lots of confusion. In this blog I hope to clarify why the changes have been made and how to teach using the new model. The first time I came across this I was hugely resistant to the changes. I enjoyed teaching energy. I believed I had energy sorted and this seemed pedantic. The problem with belief systems is that they are very hard to change with rationality (look at every election or debate!) and I took a lot of swaying. A succinct overview of the new model for energy can be found on Practical Physics . This blog attempts to explain it and give strategies for teaching it
What is energy ? This is an extremely complex question that most people think they can answer, but then realise that they probably cant.
The traditional way of teaching energy has been to list the energy types and then do the transformations.
So Chemical Energy in the Fuel is converted to Electrical Energy ……. Add an energy circus and you have some fun lessons and the students pretty much all get it. Unfortunately what they ‘understand’ is practically meaningless. That isn’t what happens. Science education is to produce scientific thinkers – People who can make decisions informed by evidence. Simplifying things to the point where they no longer relate to what really happens isn’t helpful.
One of the biggest problems faced by physics teachers is everyday language. The terminology we use in a very precise way. is often used very arbitrarily in the ‘real world’. The old approach to teaching energy wasn’t in conflict with the everyday use of terminology but is fundamentally flawed. It forms the impression that energy is something real that exists, rather than an abstract mathematical concept that doesn’t. So the chemical energy stuff is changed into the electrical energy stuff Explaining things with energy is simply meaningless. A battery doesn’t convert chemical energy into electrical energy. We can explain things with Forces – Chemicals reacting in the battery create a field* that in turn causes the electrons to experience a force and hence move.
(* If your physics understanding extends to talking about fields then use them as early as possible. Then when your students move to higher levels they will feel comfortable and familiar with the ideas of electrical/magnetic/gravitational potential, potential differences and how they relate to work done and energy.)
There is a legacy of old energy transforms even on ‘technical’ science websites so looking up how a battery works explains things in detail and then spoils it all by adding;
The stored chemical energy in the battery converts to electrical energy, which travels out of the battery and into the base of the flashlight’s bulb, causing it to light up. No it doesn’t! No wonder the students are confused!
The first question asked of the students should be : Why do we need to know about Energy ?
Energy allows us to make calculations to determine whether or not something could happen. It is simply a mathematical concept and does not make things happen. This needs to be pointed out to your students. Energy can be thought about in a similar way to another concept that allows calculations – money. If I have £10 I can buy some apples, but I cant buy a house. If I have a store of 10 Joules of energy I can lift 10 apples to a height of 1 metre, but I can’t lift a house a measurable height. As with energy, money is conserved and can always be accounted for. If I went shopping with £10 and spent £8, I would expect to return with £2. If I had less than that I would need to search for the ‘lost’ money. Similarly, energy is always conserved and accounted for. It cant however be changed from one form to another because that would mean energy is something tangible and real.
The ‘new’ approach to teaching energy will not particularly help students in their everyday world. Energy in everyday language is far too misused and the old model does not conflict with this misuse. In theory, students should not have been taught energy before secondary school, but in practice many arrive with the ideas of transformations and you will have to fight their belief system.
Why should we use this approach if the students don’t gain much in everyday knowledge?
It should create better scientific thinkers who are able to make more informed decisions. The burning of fossil fuels and the debate on renewable energy are big issues that we cant leave up to politicians who have a belief and are not interested in evidence. To develop this thinking we can have the students go right back to the original source of the energy ie the pile of coal at the power station as a finite chemical store that is being depleted and not refilled (or the nuclear store that provided the sunshine) . Alternative sources* will need to be found other than fossil fuels and the implications of energy decisions will have a huge impact on their world – These are decisions that affect their future and they need to be able to make informed choices.
(* Students confuse Sources such as Fuels, Wind, Solar with Stores such as Chemical, Kinetic, etc so it is worth spending time clarifying the differences)
Calculations about energy mean that people can make decisions about their personal use of electrical devices. To be able to argue with parents over the cost of using a laptop versus a kettle may empower your students (if not make you popular)
A much bigger issue to your students is likely to be how long their phone battery lasts and what factors might affect that. How might we charge the phone faster/ more efficiently?
Can you charge your phone with a banana? How many flaws can you see in this video?
There are many fruit charging videos out there. Are any of them viable? What is the evidence? Can your students script or produce a debunking video?
All exam boards in the UK are now using the new model in their new GCSE specifications. There is a tendency to revert back to the familiar when under pressure so ensure that your students are very well versed in the ideas of energy stores and pathways.
The energy analysis of diets and *weight loss provides many opportunities for investigating claims. The efficiency of transfer or ** from a chemical store in food to a chemical store in your body fat can be considered as well as the processes/pathways. Be very sensitive to those who may have body image issues.
*Mass should be used instead of weight and maybe Masswatchers – Se Forces Blog
**Shifting is preferred by some to transfers
Energy is an important idea in all branches of science, so you probably feel familiar with it whether your background is in physics, chemistry or biology. You may think of energy as an idea that you understand, which should not therefore be too difficult to teach.In fact it is much less straightforward than it appears, for two main reasons:
1. In science, energy is an abstract, mathematical idea. It is hard to define ‘energy’ or even to explain clearly what we mean by the word.
2. The word ‘energy’ is widely used in everyday contexts, including many which appear ‘scientific’ – but with a meaning which is less precise than its scientific meaning, and differs from it in certain respects.
The first means that, in order to communicate the scientific idea of energy to young learners, we have to simplify it – but still ensure that what we teach is clear and useful, and provides a sound basis for developing a fuller understanding later. The second means that we have to be very careful to disentangle the everyday usage of the word ‘energy’ from its scientific use, in order both to keep our own ideas clear and to avoid teaching pupils a potentially confusing mixture of the two.
Questions you might want to consider to use in your classroom:
How many Mars bars do I need to climb a mountain?
How much coal/oil do I use in a day?
When will the world’s energy resources run out?
Can the Sun supply us with our energy needs?
How hot does a catalytic converter have to be?
Can the LHC create a Higgs boson?
How can I compare phone batteries?
At school level we commonly consider energy for :
Calculation of fuel uses and costs in the domestic context
comparing energy values of different foods (from labels) (kJ)
comparing power ratings of appliances in watts (W, kW)
comparing amounts of energy transferred (J, kJ, kW hour)
domestic fuel bills, fuel use and costs
fuels and energy resources.
Passing exams – papers are going to be very focussed on Energy.
Teaching Energy Ideas
As with all concepts we need to explore the understanding and beliefs of our students.
Starting Question: What do we know about energy ?– Have them find you examples of energy in adverts or in the media or youtube.
So how is energy ‘misused’ in an everyday manner:
“I have no energy today”
“Give yourself more energy”
“Our energy will run out”
The moving pencil uses kinetic energy (QCA)
The steam [from a volcano vent] is converted into energy and transported to Europe via a 1,200-mile sea-floor cable. (The London Paper)
• Carbonaceous matter is converted to heat or other forms of energy (Physics World)
The bulb lights because energy flows from the battery to the bulb (Sophie, Year 9)
What actually do we mean by energy?
Can you answer that question?
The potential to do work? That is a rather circular answer
So what is work ?
A simplistic answer is; ‘work is done whenever a force acts on an object through a distance’ Work (J) = Force (N) x Distanced moved in direction of the Force (m)
Examples of work
Lifting a mass
Pushing a car
Pulling apart magnets that are stuck together
Breaking bonds chemically or physically (as solids melt to become a liquid)
An electron accelerating through a potential difference
A spring being stretched or compressed – squashing
A metal bar expanding as it is heated
A membrane vibrating due to a sound wave
Note that these are all ‘ ings ‘ and verbs. Something is changing, therefore energy must be being ‘used’ , however we know from the Law of Conservation of Energy that it cannot be used. This is where the new model of energy being shifted from one store to another comes in. We are moving energy from one store to another and we can measure the rate of this as Power (pathways).
So what is the new model for discussing energy? Read the Institute of Physics Supporting Physics Teaching For the specific and comprehensive treatment of Energy Stores
In financial accounting we would look at how much money we started with and where it ended up – we often aren’t too concerned in what happened to get it there. Similarly, we start talking about the energy store at the start that allows us to predict what can possibly happen. Remember energy never makes things happen. I can fill up my car with petrol in order to drive up to Scotland. I now have a chemical store large enough to get me there, but adding the fuel will not cause me to go to Scotland (thank you Trevor Plant!) Fundamentally we talk of energy stores at the starting point and the endpoint
There are a limited number of energy stores:
- chemical (e.g. fuel + oxygen) – Can be changed by bonds being made/broken
- kinetic (in a moving object) – Object speeds up or slows down
gravitational (due to the position of an object in a gravitational field) – Massive objects move closer or further apart
- vibrational – (For systems like a pendulum that is the sum of the gravitational and kinetic stores at any point in time) – Amplitude increases or decreases
- elastic (e.g. in a stretched or compressed spring) – stretched/squeezed or relaxed
- thermal or internal (in a warm object) – Material warms or cools
- magnetic ( two separated magnets that are attracting, or repelling) – distance between them
- electrostatic ( two separated electric charges that are attracting, or repelling) – distance between them
- nuclear (released through radioactive decay, fission or fusion) – fission or fusion
When things happen there is a decrease or a depletion of the original energy store and a filling of one or more energy stores (Think back to the accounting analogy) We need to consider the starting and end point.
Why no light, electrical (as in a current) or sound ? These are active processes and cannot be stored in a stable state.
A coal fire: The chemical store (fuel) is depleted and the thermal store is filled (The environment becomes warmer)
A battery-powered torch : The chemical store is depleted and the thermal store becomes filled (what about the light your students scream ! – we will come to that )
A battery-powered motor that lifts a load: The chemical store is depleted and the thermal store is filled (there is a pattern emerging here) and ……. Now we should have defined our start and end points because if our endpoint is that the load is raised and static then the gravitational store is filled, if our end point is that the load is still being raised then the kinetic store would also be being filled as well as the gravitational store.
Now we have the original stores emptying and new stores filling. What happens in between? We may well not be interested, remember that energy is about calculations. If we are interested in how energy is transferred then we need to consider the processes that we call pathways.
Energy carriers (or pathways, or transfers)
- mechanically (when a force moves through a distance)
- electrically (when a charge moves through a potential difference)
- by heating (because of a temperature difference)
- by radiation (e.g. light, microwaves, sound)
- Note that all of these pathways involve things happening and are measured in Watts . All the stores are measured in Joules
Putting these together
The general approach is having identified a situation you want to study you need to take a snapshot of the starting position – This is essential as the original store may be emptying and hence the values changing. Likewise choose an endpoint and take a snapshot.
- Choose a change to study.
- Take a snapshot (before).
- Take a snapshot (after).
- Identify the stores.
- Produce an energy description based on this analysis.
All that remains is to link the draining of the original energy stores with the pathways. A brilliant example of this is a model used by Jim Champion of Burgate School
Energy Transfer Candle Model
This is the energy model for a candle. The starting point is the Chemical store ie the fish tank. As the candle is lit the liquid is sucked down the siphon tubes. This could be the starting point snapshot. The siphon tubes model the pathways by heating and by radiation (an even better model would have a much larger bore for the by heating pathway) The thermal store at the bottom fills up and you can take your snapshot at any time. If you take your final snapshot at the point where the tank is empty then you could say that the chemical store has been emptied (though it is best to stay away from using full and empty) and the thermal store has been filled. Jim pointed out a further improvement may be to have a much wider basin at the bottom to show that energy stores become more diffuse and the energy store harder to access to do useful work. If you are prepared to be messy let it pour out onto a carpet or grass outside to show that now this thermal store cannot be transferred easily to do any more work.
Key terms to explore are;
Stores vs Sources
Transform vs Transfer (or shifting)
Pathways vs Stores
Renewable vs Non – Renewable
Energy vs Work vs Power
Energy Sentences – More Literacy
The pattern of an energy sentence is
For a (insert situation) The starting point is …….. (something static ) The end point is ………. (something else static) A …….. store is depleted and .a ……….. store is filled (there may be multiple stores) by ………ing (a process)
I lift a block of wood from the floor to the shelf. The starting point is the block on the floor, the end point is the book on the shelf. The chemical store in my muscles has been depleted and the gravitational store has been filled by mechanical working
The approach is outlined by the great Carol Davenport (@DrDav ) here a
Notice that in the UK exam boards and resources that support students have adopted this approach
AQA GCSE Physics for first exams 2018:
A system is an object or group of objects. There are changes in the way energy is stored when a system changes. Students should be able to describe all the changes involved in the way energy is stored when a system changes, for common situations. For example:
an object projected upwards
a moving object hitting an obstacle
an object accelerated by a constant force
a vehicle slowing down
bringing water to a boil in an electric kettle.
Throughout this section on Energy students should be able to calculate the changes in energy involved when a system is changed by:heating
work done by forces
work done when a current flows
BBC Bitesize Ks3 Energy is here make sure you use this rather than the older archived site that still has transformations.
The Institute of Physics SPT materials have some great materials for supporting physics teaching . They have an in depthe treatment of the whole of teaching energy here
Scales of Energy
If we are going to talk about energy we need to have some idea of the scale of energy stores and why fossil fuels are so attractive
Raising a 100g apple to a height of 1 metre requires 1 Joule of work. Doing that in 1 second represents 1 Watt of power)
So estimate how many times could you raise a 100g apple from eating 100g of chocolate? (assume you are 100% efficient!) Get the students to write down their estimates. They usually hopelessly underestimate and have guesses between 100 to 1000 times. The answer is, usually I write it down without the units – 2000 and then add kJ . Ok so thats 2 million times !
So how many chocolate bars would you need to eat to climb Mount Everest? Using Work = mgh , depending on their mass it should be around 3 – 6 bars. This is clearly wrong, so opens the debate for why not?
We can discuss:
- Efficiency (and what it means) of digestion (you can burn poo (it’s not converted to electricity – please) or convert it to biogas so it cant all be accessible for movement
- We are homeotherms (emitting around 100 Watts of heat – you might want to explore the answers given) and so need to maintain a constant temperature – Other animals don’t snakes can go for a year without eating
- Other aspects that are in your biology curriculum
- So can shining a beam of light move an object ? yes but how intense would it have to be to lift an apple a metre in the air? Similarly you would need an incredibly loud sound to move the apple.
Some interesting energy transfers to consider
Perpetual Motion Machines ! Great for discussions of the principles
Energy transfers for a crazy person
Does a fan make a room cooler? What about this set up ?
A bit of cross curricular with biology and chemistry – Do chillis really make our mouths hot and mints cool? What about chocolate?
Electrocity – http://www.electrocity.co.nz/ I love this game, it has been around for years but still is valuable
BSCS MISSION: To transform science teaching and learning through research and development that strengthens learning environments and inspires a global community of scientifically literate citizens.
http://bscs.org/interactives-3 Simple interactive wind power stations where you can change the number/height and blade length of the turbines to see how the amount of energy produced varies
Science Enhancement Programme (SEP) materials (now at National Stem Centre)
An interesting discourse on energy is here
As usual please add comments or ideas