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School Physics: Energy transfers Section 0.1 Law of conservation of energy

GCSE level Physics exam revision notes on ENERGY

Part 0.1 Defining what is energy, what is it?

and the law of conservation of energy

[Author © Dr Phil Brown PhD: Doc Brown's physics exam revision notes suitable for students of UK IGCSE & GCSE level physics courses, ~ US grades 9-10 physics [energy-0 page updated Mar 6th 2026 *]

[KEY POINTS and learning objectives for this page, after initial notes]

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ENERGY INDEX: Types of energy & energy stores, energy transfers & selected energy calculations

0.1 Introduction to 'what is energy' and the law of conservation of energy

The concept of energy emerged in the 19th century - The idea was used to explain the work output of steam engines and then generalised to understand other heat engines.

We now know energy can exist in many forms and this became a key tool for understanding chemical reactions and biological systems and not just the physics of technology and engineering.

Energy can be very simply defined something that something the ability to do work i.e. energy can make things happen - induce any sort of change in a system..

The Law of conservation of energy states that energy cannot be created but only changes from one form to another. In other words you can't use up energy, you can only change it from one form to another.

e.g. (i) braking a car involves kinetic energy converted to thermal energy from friction of the brakes and often sound energy too,

or (ii) using a battery powered torch with a metal filament bulb converts chemical potential energy into electrical energy which is then converted into heat and light.

You can also consider applying to transferring energy from one energy store to another.

You need to know what the different forms of energy stores, types of energy and examples of energy conversions and transfers between energy stores.

 In which different types of energy can exist?

You should be able to give brief description of examples of the different  forms of energy and their interconversion, brief list below and more details in sections 0.2 and 0.3.

0.2 Types of energy and energy stores and associated calculations

0.3 Lots more examples are described in Part 0.3

INDEX ENERGY: Types, stores, transfers, energy calculations

Key points for Physics - The law of conservation of energy

Information sources for Doc Brown's key points: IGCSE-GCSE physics are based on textbooks & syllabus-specifications for students taking the UK AQA, Edexcel, OCR 21st Century Science, OCR Gateway science suite, WJEC, CCEA & CIE GCSE physics 9-1 level science examinations.

A syllabus-aligned revision guide on "What is Energy?" and the Law of Conservation of Energy, tailored for students preparing for WJEC, CCEA, CIE, AQA, Edexcel, and OCR GCSE/IGCSE Physics exams:

What is Energy?

Definition

  • Energy is the capacity to do work or cause change.
  • It exists in different forms and can be stored, transferred, or transformed, but NOT destroyed - law of conservation of energy.

Types of Energy Stores

Energy Store Description Example
Kinetic Energy of moving objects A moving car
Gravitational Potential (GPE) Energy due to height A book on a shelf
Elastic Potential Energy in stretched/compressed objects A stretched spring
Thermal Energy due to temperature Hot tea
Chemical Stored in fuels, food, batteries A chocolate bar
Nuclear Stored in atomic nuclei Nuclear reactor
Electrostatic Between charged objects Static electricity
Magnetic Between magnets or magnetic materials Bar magnet

For more details see INDEX of ENERGY Types, stores, transfers, energy calculations

Energy Transfers

Transfer Mechanisms

  • Mechanically – by a force doing work (e.g. pushing)
  • Electrically – by electric current
  • By heating – due to temperature difference
  • By radiation – via waves (e.g. light, sound)

The Law of Conservation of Energy defined

Energy cannot be created or destroyed, only transferred, stored, or transformed.
In a closed system, the total energy remains constant.

Explained Examples

Scenario Energy Changes Notes
Pendulum GPE ↔ KE At the top: max GPE. At the bottom: max KE. Total energy conserved.
Rollercoaster GPE → KE → Sound/Heat Some energy dissipated as heat/sound due to friction.
Electric Kettle Electrical → Thermal Heats water; some energy lost to surroundings.
Bat hitting ball KE → KE + Sound + Thermal Energy transferred to ball; some wasted.
Trampoline KE ↔ Elastic PE ↔ GPE Energy cycles between stores as person bounces.

Exam Board Tips

  • Use correct terminology: “transferred,” “dissipated,” “useful,” “wasted.”
  • Always identify energy stores before and after.
  • Mention dissipation: energy spreads out, often as heat.
  • Understand closed versus open systems.
  • Expect quantitative questions involving KE = ½mv² and GPE = mgh.
  • Be able to draw and interpret energy diagrams.
  • Focus on practical applications and efficiency.
  • Use and interpret Sankey diagrams.
  • Emphasize real-life examples and energy conservation in systems.
  • Be ready to describe processes clearly in words.

Student Success Tips

  • Memorise key formulas:
    • Kinetic Energy: ( KE = ½mv2
    • Gravitational Potential Energy: ( GPE = mgh )
  • Practice describing energy changes in everyday devices.
  • Think like an examiner: Can you explain why energy is conserved?
  • Draw energy flow diagrams to visualise transfers.

Keywords, phrases and learning objectives on energy

Be able to explain and define what energy is.

Be able to quote law of conservation of energy, understand what it means and be able to apply the law to energy store transfers.

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INDEX for physics notes on types of energy and energy stores, energy transfers and selected energy calculations

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INDEX ENERGY: Types, stores, transfers, energy calculations

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