Science // Energy

Energy can't be created or destroyed

Explain the principle of conservation of energy (energy cannot be created or destroyed, only transferred between stores), and describe how energy is dissipated as thermal energy to the surroundings in all real processes

Ages
11 to 12
Type
Concept
Builds on
2 topics
Leads to
3 topics
Standards
2 codes

Quick check

If the learner charged their phone overnight and was asked where the electrical energy goes, could they explain what conservation of energy means — and why the charger gets warm even though that heat isn’t doing any useful work?

Ask this to see whether the topic is secure.

Topic // Mastery

What mastery looks like

What a learner can do once this topic is secure.
  • States the law of conservation of energy
  • Explains why the total energy in a closed system is always the same even though it changes form
  • Explains what dissipation means and why it happens in real machines (friction, air resistance)
  • Gives an example showing why 'wasted' energy is not lost but transferred to the surroundings

Topic // Map

Where this fits

What to learn first and what this topic opens up, with the reason for each link. Required links come first.
  • RequiredMust come first
  • HelpfulHelps, but not essential

Before this

2 topics
  • Naming types of energyRequired

    Energy // Ages 7 to 9

    Explaining conservation of energy and dissipation requires energy store and transfer vocabulary

  • Energy stores and transfersRequired

    Energy // Ages 11 to 12

    Conservation of energy is a property of energy stores and transfers — the stores and pathways model must be established first

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Energy can't be created or destroyed

Ages 11 to 12 // Concept

Leads to

3 topics
  • Efficiency, Sankey diagrams, and work doneRequired

    Energy // Ages 12 to 13

    Efficiency calculations quantify how much energy is conserved vs dissipated — conservation and dissipation must be understood first

  • Power: watts and energy per secondRequired

    Energy // Ages 12 to 13

    Power is the rate of energy transfer — the concept of energy stores and conservation must be understood before rates can be discussed

  • Reactions That Release or Absorb HeatHelpful

    Matter & Materials // Ages 12 to 13

    Conservation of energy in physical systems connects to exothermic/endothermic reactions — energy is conserved in chemical systems too

Topic // Research-informed

Teaching notes

From the Marble Skill Taxonomy. These notes have not been validated in classrooms, so treat them as a starting point for your own judgement.

The approach

For 11–12 year olds: energy conservation as bookkeeping — the TOTAL energy stays the same before and after a change, while individual stores redistribute. The central hurdle is the paradox that energy seems 'used up' (batteries go flat, pendulums die away) yet is said to be conserved. The resolution, taught explicitly, is that FUELS get used up while ENERGY is conserved but DISSIPATED — spread out, mostly to the thermal store of the surroundings, becoming too dispersed to reuse. The canonical confrontation is the pendulum or bouncing ball that doesn't return to its start height: this does not break conservation once the warmed surroundings are included in the account. Keep it qualitative-to-semi-quantitative; state the principle plainly ('energy cannot be created or destroyed, only transferred between stores'), as the objective requires, but reserve efficiency and Sankey diagrams for the next tier. NOTE: as described, this topic straddles KS3→KS4 (England) and MS→HS (NGSS): conservation-as-total-unchanged is KS3/MS, but the named law and 'dissipation' are KS4/HS.

Common misconceptions

  • Believing energy is 'used up' or 'lost' — the central paradox; in fact fuels are used up while energy is conserved and dissipated.
  • Thinking the pendulum/ball that doesn't return to its start height disproves conservation — it ignores the energy dissipated to the surrounding air.
  • Treating 'wasted' energy as destroyed rather than spread out into low-grade thermal energy in the surroundings.
  • Confusing conserving energy (a physical law that always holds) with 'saving energy' (an everyday call to use less fuel).
  • Forgetting to include the surroundings in the system, so the energy account doesn't balance.
  • Assuming a perpetual-motion machine is possible — missing that dissipation always removes usable energy from the cycle.

Useful representations

  • A locked TOTAL-energy bar above redistributing store bars (the total never changes height)
  • Dissipative processes: pendulum dying away, ball bouncing lower, car braking to rest
  • The surroundings drawn as a thermal store that grows as the useful store shrinks
  • A fuel-vs-energy panel (the battery/fuel depletes; the energy it released is traced into other stores)

Teaching practices

  • Use a closed system whose TOTAL energy is held fixed while the stores redistribute — so 'conserved' is seen as a number that doesn't change, not just a slogan.
  • ALWAYS include the surroundings / thermal store in the accounting — the 'lost' energy is dissipated there; making it visible is the key move.
  • Explicitly swap the words 'used up' and 'lost' for 'transferred' and 'dissipated' — and separate FUEL (which is used up) from ENERGY (which is conserved): 'we conserve fuels; energy conserves itself'.
  • Use the pendulum / bouncing-ball-that-doesn't-return as the canonical confrontation: it does NOT disprove conservation — account for the warmed surrounding air and the total is unchanged.
  • Build on the stores-and-pathways model: dissipation is energy spreading into the thermal store of the surroundings via heating pathways (friction, air resistance).
  • Keep it semi-quantitative (totals that reconcile) but reserve the formal law statement, efficiency and Sankey diagrams for the next tier (KS4).

Activities to try

  1. 1

    Energy budget with a locked total and a hidden-surroundings reveal

    Why it works: 'Lost' energy has not been destroyed: it is dissipated — spread out into the thermal store of the surroundings — and once you include those surroundings the total energy is unchanged. Fuels are used up; energy conserves itself.

    1. Run a dissipative process you recognise (a bouncing ball that returns lower each time, a swinging pendulum that dies away, or a car braking to a stop) and watch the useful store (gravitational or kinetic) shrink.
    2. With the surroundings hidden, notice that the energy appears to vanish — exactly the 'energy is lost' intuition.
    3. Reveal the surroundings (e.g. a toggle) and watch the 'missing' joules reappear as a growing thermal store of the air, ground or brakes, so the total is accounted for.
    4. Keep an eye on a TOTAL-energy bar held fixed throughout: it never changes height even as the store bars beneath it redistribute.
    5. In a companion panel, drag a battery/fuel going flat and trace the energy transferred from its chemical store (by electrical and light/radiation pathways) until it ends up mostly in the thermal store of the surroundings — saying aloud 'the fuel is used up; the energy is conserved'.
  2. 2

    Bend-a-paperclip prediction and feel test

    Why it works: Repeatedly bending the metal does work on it that is transferred to its thermal store, warming the bent spot — the energy is not destroyed. This is a hands-on instance of dissipation, which connects to why a useful perpetual machine is impossible: real machines always spread some energy into the surroundings, where it cannot be fully recovered to do useful work, and no machine can give out more energy than is put in.

    1. Take a metal paperclip and predict, with a reason, whether the bent spot will feel warmer, cooler, or the same if you bend it rapidly back and forth many times.
    2. Bend it about twenty times at the same spot, then feel that spot (expect only a slight, just-detectable warming, not a dramatic rise).
    3. Explain where the energy of your bending went, using the word 'dissipated' and naming the thermal store of the metal.
    4. Consider the follow-ups: feel a ball and floor after many bounces for a tiny warming; explain why you can't collect that spread-out energy to make the ball bounce back up by itself; and reason why a machine cannot keep doing useful work forever — real machines always dissipate some energy to the surroundings and you can never get more energy out than you put in.
  3. 3

    Consolidation checks on conservation and dissipation

    Why it works: Dissipated energy is still part of the total once the surroundings are included in the account — it has moved to a less useful store (mostly the thermal store of the surroundings). 'Wasteful' means more energy transferred to unwanted stores, not energy destroyed; fuels, not energy, are consumed.

    1. Answer: the pendulum stops lower than it started — what happened to the energy? (Reject the 'it was destroyed' option and identify dissipation to the surroundings.)
    2. Complete: energy is not lost but ___ (dissipated).
    3. Redistribute the 'missing' joules to the thermal store of the surroundings so the total visibly matches the starting total — semi-quantitative, with the numeric step optional where energy calculations are excluded.
    4. Categorise terms: sort 'used up' (fuel) versus 'conserved' (energy).
    5. Decide true or false: 'energy is used up' — and justify the answer.

Topic // Standards

Curriculum standards

Codes for the curriculum statements this topic maps to. Each publisher owns its standard text.
Next Generation Science Standards (NGSS) Middle School
MS-PS3-5
The national curriculum in England: Key stages 1 and 2 framework document
KS3.Sci.Phys.Energy.2

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