Physics · Visual explanation
Energy stores or transfers: which is which?
Use a system boundary and before-and-after pictures to make energy explanations clearer.
The short answer
A store describes where energy is accounted for in a system. A transfer describes a process by which energy moves between stores or crosses a system boundary. Choose the system first, then describe the stores that decrease and increase.
Conceptual illustration. Colours distinguish parts of the model.
Where the confusion starts
A transfer pathway is not an extra store. For example, heating describes a transfer process. Avoid saying energy has simply vanished when it spreads into the surroundings: it remains conserved, but may be less useful for the intended purpose.
WORK IT THROUGH
A book falls from a shelf and comes to rest on the floor.
- Ignoring air resistance, take the book and Earth as the system during the fall. Its gravitational potential store decreases while the book’s kinetic store increases.
- On impact, the kinetic store decreases. Internal energy of the book, floor and surroundings increases; some energy is transferred by sound.
- The total remains conserved when all relevant stores and surroundings are included.
CHECK YOUR UNDERSTANDING
A battery powers a motor that lifts a mass. Name a decreasing and an increasing store.
Make a prediction or write an answer before opening the explanation.
Reveal the explanation
The battery’s chemical store decreases. The gravitational potential store of the mass–Earth system increases. Some energy also spreads to the surroundings.
SEE IT. CHANGE IT. EXPLAIN IT.
Take the next step in the lesson.
Use the visual explanation in the lesson, then choose Practice to test the idea with another question.
Spotted something unclear? Send feedback. These are original teaching explanations, not predictions of future exam questions.