G3 Physics and O-Level Work, Energy & Power Hub
G3 Physics and O-Level Work, Energy and Power hub: work done, kinetic and potential energy, conservation, power, efficiency and energy resources.
Learning goals
- Recognise kinetic, potential, nuclear and internal energy stores
- Describe mechanical energy transfer by a force acting over a distance
- Describe electrical energy transfer by an electric current
- Describe energy transfer by heating due to a temperature difference
- Describe energy transfer by electromagnetic and mechanical waves
- Recall and apply Ek = ½mv² in new situations
- Recall and apply Ep = mgh near the Earth's surface in new situations
- State and apply the principle of conservation of energy
- Recall and apply work done = force × distance moved in the force direction
- Recall and apply power = energy transfer / time taken
- Calculate efficiency as useful energy output / total energy input
- Evaluate prescribed electricity-generation resources by efficiency, cost, reliability and environmental impact
This hub covers energy stores and transfer pathways, conservation, kinetic and gravitational potential energy, work, power, efficiency and resources used to generate electricity.
Before you begin:
- Core Exam Skills (units, graphs, command words)
- Forces for forces and displacement
- Kinematics for speed and motion graphs
Follow this order:
What you will learn
The five lessons build the Energy topic in this order:
- identify energy stores and the four transfer pathways: mechanically, electrically, by heating and by waves;
- calculate kinetic and gravitational potential energy and apply conservation of energy;
- calculate work, power and efficiency; and
- compare the named renewable and non-renewable resources for electricity generation using efficiency, cost, reliability and environmental impact.
Lessons
Energy stores and transfers
Stores, four transfer pathways and conservation of energy.
KE, GPE and conservation calculations
Apply ½mv², mgΔh and energy accounting to unfamiliar situations.
Work done
Calculate W = Fd and identify when a force transfers no energy.
Power and efficiency
Calculate rates of energy transfer and useful output ratios.
Energy resources
Compare resources using efficiency, cost, reliability and environmental impact.
Revision
Quick Reference
| Quantity | Formula | Unit |
|---|---|---|
| Work done | W = Fd (distance moved in the force’s direction) | joule (J) |
| Kinetic Energy | Eₖ = (1/2)mv² | Joule (J) |
| Gravitational Potential Energy | Δ Eₚ = mgΔ h | Joule (J) |
| Power | P = W/t = E/t | Watt (W) |
| Efficiency | (Useful Output)/(Total Input) × 100% | % (no unit) |
Units and conversions
- 1 J = 1 N m and 1 W = 1 J s⁻¹.
- Near Earth, g ≈ 10 N kg⁻¹ (also 10 m s⁻²).
- In practical-electricity questions, 1 kWh = 3.6 × 10⁶ J.
Definitions and method to recall
- Principle of Conservation of Energy: Energy cannot be created or destroyed. It is transferred between stores, so total energy remains constant.
- Work Done: Product of force and the distance moved in the direction of the force.
- Power: The rate of doing work (or rate of energy transfer).
- Efficiency: The ratio of useful energy output to total energy input.
- Gravitational potential energy change: use vertical height change (Δ h), not path length.
Energy method template
- List the initial and final energy stores.
- State: “Energy input = useful output + energy dissipated” where relevant.
- Use the correct formula(s) and consistent SI units.
- If efficiency is involved, write it as a ratio first, then convert to
%if asked.
Visual snapshots
These are schematic. Use them to remember key relationships quickly.
Kinetic energy depends on speed squared
A curved (quadratic) kinetic energy–speed relationship: doubling speed quadruples kinetic energy.
Scroll across the graph to read all labels.
View figure data
| Speed (m s⁻¹) | E_k vs v |
|---|---|
| 0 | 0 |
| 2 | 4 |
| 4 | 16 |
| 6 | 36 |
| 8 | 64 |
| 10 | 100 |
Don’t assume the relationship is linear just because the axes are labelled; use the formula (this chart is schematic).
Data table
| Energy flow | Example |
|---|---|
| Total input | 100 |
| Useful output | 60 |
| Dissipated to surroundings | 40 |
Top exam traps
- Work direction: Distance d must be in the same direction as the force F. If you lift a bag while walking horizontally, the lifting force does no work on the bag’s horizontal motion.
- Power vs Energy: A machine with high power does the same work faster, not more work.
- Efficiency Limits: Efficiency can never be > 100%. If you get > 100%, check your input/output swap.
- Square relation: Eₖ depends on v². If speed doubles, Kinetic Energy quadruples (2² = 4).
- GPE Reference: h is vertical height change. The path taken (ramp vs lift) doesn’t change Δ Eₚ, only the force required.
- kW vs W: Convert
kWtoWbefore using P = E/t (1 kW = 1000 W). - kWh vs J: For energy in joules, use 1 kWh = 3.6 × 10⁶ J.
- g units: You may see g as N kg⁻¹ or m s⁻²; both are equivalent near Earth.
- Efficiency as decimal vs %: If you use a percentage, don’t multiply by 100 again.
Practice
Work, Energy and Power Quiz
Check definitions, formula choice and common misconceptions.
Structured practice
Apply energy accounting and comparison skills in longer questions.
Work, Energy & Efficiency Explorer
Choose equations and trace useful and dissipated energy in interactive exam-style scenarios.
Household electricity application
Apply power and energy ideas to appliance ratings and energy use.
Start with the Energy check, which covers energy stores and transfers, efficiency and energy resources. Return to the lesson linked with any question you cannot yet explain in a complete sentence.
Finish with Work, Energy and Power structured practice to show full calculation methods and explanations.
Continue learning
Continue to Pressure, or use the A-Level Work, Energy and Power hub only when you are ready for extension material such as the work–energy theorem.
Course and syllabus information
- Course
- SEC G3 Physics
- Edition
- SEC G3 Physics 2027