Allow about 15 mins

A lot of time has spent in the physics-teaching community discussing the language around energy. Anecdotal evidence suggests that this has caused anxiety and concern from both specialist and non-specialist physics teachers.

Whilst in our development of these resources we have tried to be very careful with our choice of language; the good news is that you should not need to worry to the same extent.

The most important part in your teaching of energy is to ensure that the main ideas are covered, and it is these concepts that you should focus on. As a reminder, these include:

• The amount of energy in a store is calculable.
• The total energy in a system is always conserved.
• Knowing the values of energy stores may tell us whether an action can happen (but not why it happens, or if it will happen).
• If we compare the amounts of energy in stores before and after an event, then we can calculate efficiencies.
• Calculating the energy values as one store empties and another fills enables us to make quantitative predictions about physical changes, such as changes to temperature and speed.

As you grow in confidence teaching this topic you may wish to think again about your language, and the words and phrases you use may well develop over time as your experience of teaching energy grows. Therefore, this may be a section that you come back to.

What follows is some guidance from the Institute of Physics about the language of energy, and some of the reasons why being careful with the language can help avoid student misconceptions. It should be helpful to you now, but hopefully you can also look back at it when you have spent more time teaching this topic.

Language choices

Overriding points to keep in mind:

1. it is all too easy to represent energy as though it is something physical, like a liquid but it is best not to;
2. energy is a quantity; aim to represent it as such;
3. the role of energy in physics and physics discussions is as an analytical tool; discuss it in those terms.

Stores and pathways

Stores are a scaffold for energy expressions and calculations (up to age 14). They are not real; they represent an imaginary store associated with a system. In short, they represent an amount of energy measured in joules.

Pathways are placeholders for power expressions and calculations. There are four pathways that are most useful:

• working mechanically,
• working electrically,
• heating by contact,
• heating by radiation.

They represent a way of describing the rate at which energy is transferred – measured in watts.

Adjectives and adverbs

Adjectival energy labels like “elastic energy”, “kinetic energy” or “xxx energy” imply that energy exists in different forms or types. It doesn’t, the quantity stored is always just energy.

Adverbs provide a clearer description. For example, “energy stored gravitationally” confirms that the quantity is still energy but, it is stored in a particular way by the system.

Use phrases like:       

“energy stored elastically”,
“energy stored kinetically”,
“energy stored thermally”.

To emphasise that the quantity stored is just energy, but the store itself is different:

Use phrases like:       

“kinetic store of energy”,
“gravitational store of energy”,
“elastic store of energy”.

Avoid phrases like:      

“kinetic energy store”,
“gravitational energy store”,
“elastic energy store”.

Which stores do we need?

Limit the number of energy stores to those that can be calculated and identified at any given instant.

It is likely that you will need the following for either of these constructions: “xxx store of energy” or “energy stored xxxly”:

Where xxx is one of: gravitational, elastic, kinetic, chemical, thermal, nuclear, electric, magnetic, vibrational.

Energy is stored by systems

It is useful to discuss the energy stored by a system rather than suggesting that energy is possessed by objects. There is a value that is associated with a system depending on the arrangement or movement of its constituents; and that value is the amount of energy stored, measured in joules.

Use phrases like:       

“the amount of energy stored gravitationally by the Earth/book system” or,
“the energy in the chemical store associated with the food and oxygen”.

Avoid phrases like:    

“the gravitational energy of the book”;
“the chemical energy of the food”

It is worth noting that food and fuels do not store energy; they require oxygen to combust. Therefore, it is the systems of the food/fuel plus oxygen that stores energy.

Energy is conserved

Energy is a conserved quantity. The energy stored before an event is the same as the energy stored after it – even if it is stored in a different way. It is this feature that enables us to do powerful calculations.

Use phrases like:       

“energy is stored by the fuel/oxygen system”,
“energy is transferred – from one system to another”.

Phrases that imply energy can be created or used up are best avoided.

Avoid phrases like:    

“energy is created in the reaction”,
“the wind turbine produces energy”,
“energy is used to make the car move”,
“energy is lost”.