Module 6
Energy
Quick-reference revision notes for parents.
6.1 Food and fuels
- Food and fuels both store chemical energy, released by combustion (fuel) or respiration (food).
- Energy in food is measured in kJ (kilojoules) — labels often show "energy per 100g".
- Common fuels: coal, oil, natural gas, wood, biofuels.
6.2 Energy resources
| Type | Examples | Pros / cons |
|---|---|---|
| Non-renewable | Coal, oil, gas, nuclear | Reliable, energy-dense; will run out, pollution / waste |
| Renewable | Wind, solar, hydro, tidal, geothermal, biomass | Won't run out, low CO₂; weather-dependent, can affect habitats |
6.3 Energy adds up — conservation of energy
Energy cannot be created or destroyed — only transferred from one store to another.
Energy stores include: chemical, kinetic, gravitational, thermal, elastic, nuclear.
Falling: gravitational store → kinetic store. Squashed: kinetic → elastic. Bouncing back up: elastic → kinetic → gravitational. Some energy is dissipated as thermal and sound each bounce, so the ball doesn't reach its starting height.
6.4 Energy and temperature
- Temperature: how hot something is (°C) — depends on the average kinetic energy of its particles.
- Heat (thermal energy): the total energy in a substance — depends on temperature AND amount.
- Heat always flows from hot → cold (until they reach the same temperature: thermal equilibrium).
6.5 Energy transfer: particles (conduction and convection)
- Conduction: energy passes through a solid as vibrating particles bump into their neighbours. Metals conduct best because of free electrons.
- Convection (in liquids and gases): warm fluid is less dense → rises; cooler fluid sinks. Sets up a convection current.
6.6 Energy transfer: radiation
- Heat radiates as infrared waves — no particles needed (works through a vacuum: that's how heat reaches us from the Sun).
- Dark, matt surfaces are good at emitting AND absorbing radiation.
- Light, shiny surfaces reflect radiation (poor emitters and absorbers).
6.7 Energy transfer: forces (work done)
When a force moves something, energy is transferred — we say work is done. Energy is also transferred by sound, electricity and waves.
6.8 Energy and power
Power = the rate of energy transfer.
power = energy ÷ time (watts = joules ÷ seconds)
A 60W bulb is on for 30s. How much energy is transferred?
energy = power × time = 60 × 30 = 1800 J
Domestic appliances are rated in W or kW. Electricity bills measure energy in kilowatt-hours (kWh): 1 kW × 1 hour.
Quick reference
- Energy can be transferred but not created or destroyed
- Conduction: solids (vibrating particles). Convection: fluids (warm rises). Radiation: infrared, no particles needed
- Dark/matt surfaces emit and absorb best; shiny reflect
- Power = energy ÷ time (W = J ÷ s)
- Energy = power × time