ABLEEnergy Stores & Transfers
Energy Stores
Energy can be stored in different ways: kinetic (movement), gravitational potential (height), elastic potential (stretched/compressed), thermal (heat), chemical (food/fuel), nuclear, electrostatic, and magnetic.
Kinetic Energy
The energy an object has due to its motion. It depends on mass and velocity.
KE = ½mv²
Gravitational Potential Energy
The energy an object has due to its position in a gravitational field. It depends on mass, gravitational field strength, and height.
GPE = mgh
Conservation of Energy
Energy cannot be created or destroyed, only transferred from one store to another. The total energy in a closed system remains constant.
Efficiency
Efficiency measures how much of the input energy is usefully transferred. Wasted energy is usually dissipated as thermal energy to the surroundings.
efficiency = (useful energy output ÷ total energy input) × 100%
Key Points
- Energy is always conserved — it cannot be created or destroyed
- KE = ½mv² — kinetic energy depends on velocity squared
- GPE = mgh — gravitational potential energy depends on height
- Efficiency is always less than 100% in real systems
Exam Tips
- When using KE = ½mv², remember to square the velocity, not the mass
- For energy transfer questions, identify the start and end energy stores
- Show the conservation of energy equation when solving multi-step problems