A SYSTEM is an object or group of objects being studied.
When a system changes, energy is TRANSFERRED between different energy stores — but the TOTAL energy always stays the same.
Examples of systems changing:
A ball thrown upwards: kinetic store → gravitational potential store.
A falling object: gravitational potential store → kinetic store.
A battery powering a bulb: chemical store → thermal store + light radiation.
A stretched spring released: elastic potential store → kinetic store.
The Eight Energy Stores
Energy can be held in eight different STORES:
1. KINETIC — energy stored in any moving object. Cars, wind, flowing water.
2. THERMAL (INTERNAL) — energy stored in the random movement of particles. Hot water, warm air.
3. CHEMICAL — energy stored in chemical bonds. Food, fuel, batteries.
4. GRAVITATIONAL POTENTIAL — energy stored in an object due to its height. A book on a shelf, a raised hammer.
5. ELASTIC POTENTIAL — energy stored in a stretched or compressed object. A stretched spring, a drawn bow.
6. MAGNETIC — energy stored in magnetic fields.
7. ELECTROSTATIC — energy stored between charged objects.
8. NUCLEAR — energy stored in atomic nuclei. Released in nuclear reactions.
Think of energy stores like BANK ACCOUNTS — energy moves between accounts but you can never create money from nowhere. The total always stays the same.
Energy Pathways
Energy is transferred between stores via PATHWAYS:
MECHANICAL WORK — a force acting through a distance. Pushing, lifting, stretching.
ELECTRICAL WORK — charge moving through a potential difference. Current in a circuit.
HEATING — thermal energy transferred by conduction, convection or radiation.
RADIATION — energy transferred by waves (light, infrared, sound etc.).
EXAMPLES of complete energy transfers:
Kettle: chemical store → thermal store (water + surroundings) via heating and electrical work.
Dropped ball: gravitational PE store → kinetic store → thermal store (on impact) via mechanical work.
Car: chemical store → kinetic store + thermal store (engine heat, friction, air resistance).
The LAW OF CONSERVATION OF ENERGY: energy cannot be created or destroyed — only transferred between stores or dissipated.
⚠️ Common Mistake
STORES are where energy is held (kinetic, chemical, thermal etc.). PATHWAYS are how it moves (heating, mechanical work, electrical work, radiation). 'Heat' is a transfer pathway — not a store. You store THERMAL energy, not 'heat'.
📐 Variables
EEnergy (E) is measured in joules (J)
📌 Key Note
8 energy stores: kinetic, thermal, chemical, gravitational PE, elastic PE, magnetic, electrostatic, nuclear. 4 pathways: mechanical work, electrical work, heating, radiation. Law of conservation of energy: energy cannot be created or destroyed.
🎯 Matching Activity — Store or Pathway?
Sort each into an energy store or a transfer pathway. — drag the symbols on the right to match the component names on the left.
Energy store
Drop here
Energy store
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Energy store
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Transfer pathway
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Transfer pathway
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Transfer pathway
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Electrical work — charge moving through a potential difference
Chemical — energy held in the bonds of fuels, food and batteries
Radiation — energy transferred by light, infrared or sound waves
Heating — thermal energy transferred from hot to cold objects
Elastic potential — energy held in a stretched spring or compressed gas
Gravitational potential — energy held due to an object's height above ground
🎯 Test Yourself
Question 1 of 2
1. A ball is thrown upwards and slows down. Which energy transfer is occurring?
2. Which of the following is an energy TRANSFER PATHWAY, not an energy store?
⭐ How Well Do You Understand This Topic?
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