Energy stores
- Energy can be stored as kinetic, gravitational potential, elastic potential, thermal (internal), chemical, magnetic, electrostatic or nuclear energy.
- A moving object has energy in its kinetic store; a raised object has energy in its gravitational potential store.
Ways energy is transferred
- Mechanically: when a force moves an object (work done).
- Electrically: when a current flows.
- By heating, and by radiation such as light and sound.
Conservation of energy
- Energy can be transferred usefully, stored or dissipated, but it cannot be created or destroyed.
- In a closed system, the total energy stays the same.
- Wasted energy is usually dissipated to the surroundings as thermal energy.
Equations to learn
- Kinetic energy: Eₖ = ½ m v²
- Gravitational potential energy: Eₚ = m g h (g = 9.8 N/kg on Earth; Edexcel and OCR papers use 10 N/kg)
- Elastic potential energy: Eₑ = ½ k e²
- Work done: W = F s
Reducing unwanted energy transfers
- Lubrication reduces friction between moving parts.
- Thermal insulation reduces the rate of heat loss from buildings.
- Thicker walls made of materials with low thermal conductivity reduce energy transfer.
Key terms
- Energy store
- A way energy is held, such as kinetic, thermal or chemical.
- Kinetic energy
- Energy an object has because it is moving: Eₖ = ½mv².
- Gravitational potential energy
- Energy gained by raising an object: Eₚ = mgh.
- Elastic potential energy
- Energy stored in a stretched or squashed object: Eₑ = ½ke².
- Dissipated
- Spread out to the surroundings and wasted, usually as thermal energy.
- Closed system
- A system where no energy enters or leaves, so the total stays the same.
- Work done
- Energy transferred when a force moves an object: W = Fs.
- Conservation of energy
- Energy cannot be created or destroyed, only transferred.