Energy stores and transfers · Grade 7

Energy is never made or destroyed; it is moved from one store to another. A torch moves energy from a chemical store to light and heat; a falling apple moves it from a gravitational store to a kinetic store. Machines are never perfect, so some energy is always wasted, usually heating the surroundings.

Key facts

• Energy stores: kinetic, gravitational potential, elastic potential, chemical, thermal, nuclear (and magnetic, electrostatic).
• Energy is transferred by forces (mechanical work), electric current, heating, and waves (light and sound).
• Conservation of energy: total energy in = total energy out.
• Wasted energy usually ends up in the thermal store of the surroundings.
• Efficiency = useful energy out ÷ total energy in (× 100 for %).
• Sankey diagrams show energy transfers: arrow widths are proportional to the energy.

Worked examples

Other years

• Energy stores and transfers · Grade 4
• Energy stores and transfers · Grade 5
• Energy stores and transfers · Grade 6
• Energy stores and transfers · Grade 8
• Energy stores and transfers · Grade 9