Conservation of energy

OCR

GCSE

The principle of conservation of energy is a fundamental law of physics stating that energy cannot be created or destroyed, only transferred, stored, or dissipated. This topic explores the quantitative relationships between major energy stores, specifically kinetic, gravitational potential, and elastic potential energy. It necessitates an understanding of energy transfer pathways, the calculation of work done and power, and the analysis of efficiency within closed and open systems.

Objectives

Exam Tips

Pitfalls

Key Terms

Mark Points

What You Need to Demonstrate

Key skills and knowledge for this topic

Award 1 mark for stating that energy cannot be created or destroyed, only transferred between stores
Award 1 mark for identifying the correct transfer pathway (e.g., mechanical work done against friction transfers energy to thermal store)
Award 1 mark for calculating the final velocity by equating GPE lost to KE gained (mgh = 0.5mv²)
Award 1 mark for explaining that 'wasted' energy is dissipated as thermal energy to the surroundings, increasing their temperature
Award 1 mark for correct calculation of efficiency as a ratio or percentage, ensuring the value is not greater than 1 or 100%

Marking Points

Key points examiners look for in your answers

Award 1 mark for stating that energy cannot be created or destroyed, only transferred between stores
Award 1 mark for identifying the correct transfer pathway (e.g., mechanical work done against friction transfers energy to thermal store)
Award 1 mark for calculating the final velocity by equating GPE lost to KE gained (mgh = 0.5mv²)
Award 1 mark for explaining that 'wasted' energy is dissipated as thermal energy to the surroundings, increasing their temperature
Award 1 mark for correct calculation of efficiency as a ratio or percentage, ensuring the value is not greater than 1 or 100%

Examiner Tips

Expert advice for maximising your marks

💡When describing energy changes, always identify the 'store' at the start and the 'store' at the end, plus the 'pathway' (e.g., 'Chemical store transferred mechanically to Kinetic store')
💡In calculations involving GPE and KE conservation where mass is not given, remember that mass often cancels out (gh = 0.5v²); this is a common Higher Tier trick
💡For efficiency questions, check your answer immediately: if the result is greater than 1 (or 100%), you have inverted the equation

Common Mistakes

Pitfalls to avoid in your exam answers

Stating that energy is 'lost' or 'used up' rather than dissipated or transferred to a thermal store of the surroundings
Forgetting to square the velocity (v²) when calculating Kinetic Energy, leading to significantly incorrect values
Failing to convert units before substitution, such as using mass in grams instead of kilograms or distance in km instead of m
Confusing 'power' with 'energy' when explaining the rate of transfer

Key Terminology

Essential terms to know

Energy stores and transfer pathways

The Law of Conservation of Energy

Work done and Power

Gravitational potential, kinetic, and elastic potential energy calculations

Efficiency and energy dissipation

Thermal conductivity and insulation

Likely Command Words

How questions on this topic are typically asked

Calculate

Explain

Describe

Suggest

Compare

Practical Links

Related required practicals

•{"code":"PAG 5","title":"Investigation of effectiveness of thermal insulation","relevance":"Demonstrates reduction of unwanted energy transfers (dissipation) via thermal conductivity"}

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