Burn fuel, charge a phone, lift a weight: in every case energy simply shifts from one store to another. Nothing is ever created and nothing is ever destroyed. The accounting always balances, even when energy spreads out into the surroundings where it is harder to use.
Energy is held in stores (kinetic, gravitational potential, elastic, chemical, nuclear, internal/thermal, electrostatic) and moved between them by transfers (mechanical work, electrical, heating, and waves). The total energy is always conserved.
Energy can be stored and transferred from one store to another, but it cannot be created or destroyed.
This is the principle of conservation of energy.
Choose a process and follow the energy as it moves between stores. The bars rise and fall, but add them up and the total never changes.
Four quick checks on stores, the ways energy moves, and conservation. Each correct answer earns XP and lights this skill on your star map.
Which of these is an energy store?
Energy moved by an electric current is transferred...
The principle of conservation of energy states that energy cannot be...
When energy is described as "wasted", it has usually been transferred to the surroundings as...
A store is where energy is held; a transfer is how it moves. Keep the two ideas separate: "heating" and "electrical" are not stores, they are the routes energy takes between stores.
| Energy stores | Ways energy is transferred |
|---|---|
| Kinetic (movement) | Mechanically, by a force doing work |
| Gravitational potential (height) | Electrically, by an electric current |
| Elastic (stretched or squashed) | By heating, when there is a temperature difference |
| Chemical, nuclear | By waves, such as light or sound |
| Internal (thermal), electrostatic |
When energy is "used up", it has not vanished. It has been transferred to the surroundings, usually as thermal energy, where it spreads out and becomes far less useful. The total amount of energy is exactly the same as before, so never write that energy is lost or destroyed.
Unlocks once the four checks above are done. Worth more XP, written in the style of Paper 2.
A battery drives a motor that slowly lifts a load. The main energy transfer is from a chemical store to...
A torch is powered by a 1200 J chemical store. If 200 J ends up as useful light, the remaining 1000 J is...
As an apple falls from a tree, energy is transferred from a gravitational potential store to a kinetic store. This transfer happens...
This skill is now lit gold on your star map. Keep the chain going.