Whole Earth Curriculum WEC

Lesson 05 — Conservation of Energy and Energy Transformations

Learners explain the **law of conservation of energy** — energy is never created or destroyed, only transformed — and analyze **energy transformations and efficiency** in a real system. They see that "lost" energy is never gone; it spreads as heat, and efficiency measures how much stays useful.

D06 P3: Intellectual & Cognitive Awareness D06.S3 55 minutes Draft

Objectives

Essential question

How is energy conserved yet transformed, and what does efficiency mean in a real system?

conservation of energytransformationefficiencykineticpotentialthermalchemicalelectrical

Materials

Standard materials

Low-tech / no-cost

Enriched / lab & device

Works in different contexts

A chain showing energy changing form from chemical to thermal to kinetic to electrical to light, with a heat arrow leaving at each step and a note that energy is conserved but some always spreads as heat
A chain showing energy changing form from chemical to thermal to kinetic to electrical to light, with a heat arrow leaving at each step and a note that energy is conserved but some always spreads as heat

Lesson 5 — Conservation of Energy and Energy Transformations

Summary

Learners explain the law of conservation of energy — energy is never created or destroyed, only transformed — and analyze energy transformations and efficiency in a real system. They see that “lost” energy is never gone; it spreads as heat, and efficiency measures how much stays useful.

Objectives

  • Explain the law of conservation of energy and analyze energy transformations and efficiency in a real system. (D06.S3.09.01)

Connection

Strike a match and you feel the point where chemical energy becomes thermal (heat) and light. Rub your hands together on a cold day and motion becomes warmth. In every case, nothing is made from nothing: the energy was already there, locked in the match or in your moving muscles, and it only changed costume. The rule is absolute and has no exceptions ever observed: energy is conserved. The catch — and it matters for every engine, battery, and body on Earth — is that each change drops a little energy as spread-out heat that is hard to use again.

Materials

  • Energy-transformation chain sheet
  • Efficiency calculation card

Preparation

  • Copy the chain sheet and efficiency card.
  • Retrieval: from Grade 6, recall the forms of energy (kinetic, potential, thermal, chemical, electrical); from Grade 8, recall atoms, elements, and reactions.

Facilitator note

This lesson is written to the learner (“you”). The two ideas to land: (1) conservation of energy — energy is neither created nor destroyed, only transformed from one form to another (kinetic, potential, thermal, chemical, electrical, light); (2) efficiency — in any real transformation, some energy always spreads as heat into the surroundings, so efficiency = useful energy out ÷ total energy in, always less than 100%. Use a worked example first (S-011): a power plant chain chemical → thermal → kinetic → electrical → light, with heat leaving at each step. The critical-thinking lens: the word “lost” is a trap — the heat is not gone, it is spread out and no longer available to do useful work; say “spread as heat,” not “destroyed.” The technology lens: efficiency is where physics meets engineering — a more efficient engine, battery, or lamp does more with the same energy, which is why efficiency is a design goal everywhere (S-256, S-435). The environment lens: because no process is 100% efficient, every energy source carries a heat and waste cost — and choosing between sources is partly a question of how much energy we waste as heat and how we make the energy in the first place (S-256). The global lens: the same law governs a rice cooker in Asia, a wind turbine in Europe, and a body anywhere — energy conservation is universal. Keep the numbers honest and hedged; efficiency is always less than 1 (or 100%), never exactly, in any real machine.

Procedure

  1. Recall (5 min). From Grade 6: name five forms of energy. Which two do you feel when you rub your hands together?
  2. Meet conservation (8 min). Energy is never created or destroyed — only transformed. Say the rule in your own words, then again in a partner’s.
  3. Trace a chain (12 min). Worked example: a power plant. Chemical (fuel) → thermal (heat) → kinetic (turning turbine) → electrical (current) → light (a lamp). Label each step on the sheet, and mark where heat spreads out at every arrow.
  4. Meet efficiency (12 min). Efficiency = useful energy out ÷ total energy in. If a lamp takes 100 J and gives 15 J of light, its efficiency is 15%. The other 85 J is not gone — it has spread as heat. Do the three practice cases.
  5. Peer-check (8 min). Swap sheets. Did each case divide output by input? Did each answer stay below 100%?
  6. Close (10 min). Energy is never lost — but every change taxes it a little heat. Efficiency is the honest score of how well we keep it useful.

Differentiation

  • Support: Provide the chain pre-labeled; the learner only fills the efficiency calculation using the formula with the numbers already arranged.
  • Extension: Compare the efficiency of two real devices (an incandescent lamp vs. an LED, a gasoline vs. an electric motor) and explain the difference in everyday terms.

Assessment

  • Formative (observation): Can the learner state conservation of energy and compute efficiency for a simple input/output pair, explaining where the “lost” energy went?
  • Portfolio artifact: The labeled chain and the three efficiency calculations, kept in the portfolio.

Home connection

Pick a device at home — a kettle, a phone charger, a bicycle. Trace its energy path in forms, and ask where the heat spreads out along the way.

Resources