Introduction

Energy is constantly moving from one place to another.

A battery powers a flashlight, a kettle boils water, a car accelerates, and the Sun warms Earth. In each case, energy is being transferred.

Modern physics explains these processes using two important ideas:

• Energy stores — where energy is held.
• Energy transfer pathways — how energy moves between stores.

Understanding the difference between these two ideas makes it much easier to analyze physical systems and explain how energy is conserved.

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What is an Energy Transfer Pathway?

An energy transfer pathway is the process by which energy moves from one energy store to another.

Unlike an energy store, a transfer pathway does not store energy.

Instead, it describes how energy is transferred.

There are four main energy transfer pathways:

• Mechanical work
• Electrical work
• Heating
• Waves

Every energy transfer can be described using one or more of these pathways.

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Energy Stores vs Energy Transfer Pathways

One of the most important ideas in physics is to distinguish between where energy is stored and how it is transferred.

For example:

A battery contains energy in its chemical energy store.

When connected to a lamp:

Chemical store
→ electrical transfer
→ Internal energy store of the lamp + energy transferred by light waves.

The battery stores energy.

The electric current transfers it.

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Mechanical Work

Mechanical work transfers energy when a force acts through a displacement.

Whenever a force causes an object to move, energy is transferred mechanically.

Examples include:

• Pushing a shopping trolley.
• Lifting a box.
• Compressing a spring.
• Braking a bicycle.
• A falling object accelerating.

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Example: Lifting a Backpack

A student lifts a backpack from the floor.

Energy transfer:

Chemical energy store (muscles)

↓

Mechanical work

↓

Gravitational potential energy store (backpack)

The person's muscles transfer energy to the backpack by doing mechanical work.

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Electrical Work

Electrical work transfers energy when electric charges move through a circuit.

Examples include:

• A battery powering a flashlight.
• Charging a mobile phone.
• Running an electric fan.
• Operating a television.
• Charging an electric vehicle.

Electrical work transfers energy from electrical sources into other energy stores.

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Example: Electric Fan

Chemical energy store (battery)

↓

Electrical transfer

↓

Kinetic energy store (fan blades)

↓

Internal energy store (motor and air)

Not all of the transferred energy becomes useful motion. Some is dissipated as heating.

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Heating

Heating transfers energy because of a temperature difference.

Energy always moves:

From a hotter object to a cooler object.

Heating increases the internal (thermal) energy store of the cooler object.

Examples include:

• A saucepan heating on a stove.
• A hot drink cooling.
• Warm air heating a room.
• A spoon becoming hot in soup.
• A radiator warming a classroom.

Heating may occur by:

• Conduction
• Convection
• Thermal radiation

These processes are explored in greater detail in the Thermal Energy course.

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Example: Boiling Water

Chemical energy store (gas)

↓

Heating

↓

Internal energy store (water)

The gas transfers energy to the water by heating.

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Transfer by Waves

Energy can also be transferred by waves.

Examples include:

• Light.
• Infrared radiation.
• Sound.
• Microwaves.
• Radio waves.
• X-rays.

The waves carry energy without requiring the movement of matter from one place to another.

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Example: Sunlight

Nuclear energy store (Sun)

↓

Light waves

↓

Internal energy store (Earth)

The Sun transfers energy to Earth through electromagnetic waves.

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Comparing the Four Transfer Pathways

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Analyzing Energy Transfers

To analyze any situation:

Step 1

Identify the starting energy store.

Step 2

Identify the transfer pathway.

Step 3

Identify the final energy store(s).

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Example 1: Flashlight

Starting store:

Chemical energy store (battery)

Transfer pathway:

Electrical work

Final stores:

• Internal energy store of lamp
• Light waves
• Internal energy store of surroundings

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Example 2: Roller Coaster

Top of hill:

Gravitational potential energy store

↓

Mechanical work by gravity

↓

Kinetic energy store

↓

Heating (friction)

↓

Internal energy stores of wheels, track, and air

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Example 3: Bow and Arrow

Chemical energy store (muscles)

↓

Mechanical work

↓

Elastic energy store (bow)

↓

Mechanical work

↓

Kinetic energy store (arrow)

↓

Sound waves + Internal energy stores

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Example 4: Electric Kettle

Chemical energy store (fuel at power station)

↓

Electrical transfer

↓

Internal energy store (heating element)

↓

Heating

↓

Internal energy store (water)

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Energy Flow Diagrams

An energy flow diagram shows:

• The starting energy store.
• The transfer pathway.
• The final energy store(s).

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Example 1: Falling Ball

Gravitational potential energy store

↓

Mechanical work

↓

Kinetic energy store

↓

Heating (air resistance)

↓

Internal energy stores of air and ball

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Example 2: Battery-Powered Car

Chemical energy store (battery)

↓

Electrical work

↓

Kinetic energy store (car)

↓

Heating

↓

Internal energy stores of tyres, road, and air

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Example 3: Toaster

Electrical transfer

↓

Internal energy store (heating elements)

↓

Heating + Infrared waves

↓

Internal energy store (bread)

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Constructing an Energy Flow Diagram

Follow these steps:

Step 1

Identify the system.

Example:

A cyclist riding a bicycle.

Step 2

Identify the starting energy store.

Chemical energy store (food).

Step 3

Identify the transfer pathway.

Mechanical work.

Step 4

Identify the final energy store.

Kinetic energy store (bicycle).

Step 5

Include other transfers.

Heating (friction).

Sound waves.

Internal energy stores of surroundings.

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Conservation of Energy

Energy cannot be created or destroyed.

Instead:

• Energy leaves one store.
• It is transferred by one or more pathways.
• It enters one or more new stores.

For example:

When braking a bicycle:

Kinetic energy decreases.

The energy is transferred mechanically by friction into:

• Internal energy of the brakes.
• Internal energy of the tyres.
• Internal energy of the road.
• Internal energy of the surrounding air.

The total energy remains constant.

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Everyday Examples

Walking

Chemical energy store (food)

↓

Mechanical work

↓

Kinetic energy store (body)

↓

Heating

↓

Internal energy store (muscles and surroundings)

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Solar Panel

Nuclear energy store (Sun)

↓

Light waves

↓

Electrical transfer

↓

Chemical energy store (battery)

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Microwave Oven

Electrical transfer

↓

Microwaves

↓

Internal energy store (food)

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Loudspeaker

Electrical transfer

↓

Sound waves

↓

Internal energy store (air and listener's ear)

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Common Mistakes

Avoid these common misconceptions:

• Heat is not an energy store. Heating is an energy transfer pathway.
• Electricity is not an energy store. Electrical currents transfer energy.
• Light and sound are not energy stores. They are waves that transfer energy.
• Energy is never "used up." It is transferred between stores.
• Most real systems involve more than one energy store and more than one transfer pathway.
• Dissipated energy is still conserved. It has simply been transferred into less useful internal energy stores.

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Key Vocabulary

• Energy Store – A way in which energy is held within an object or system.
• Energy Transfer Pathway – A process by which energy moves from one store to another.
• Mechanical Work – Energy transferred when a force acts through a displacement.
• Electrical Work – Energy transferred by moving electric charges.
• Heating – Energy transferred because of a temperature difference.
• Waves – Oscillations that transfer energy from one place to another.
• Energy Flow Diagram – A diagram showing how energy moves between stores.
• Internal Energy Store – The energy associated with the particles inside a substance.
• Conservation of Energy – The principle that energy cannot be created or destroyed, only transferred.

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Summary

• Energy is transferred between energy stores through four transfer pathways: mechanical work, electrical work, heating, and waves.
• Energy stores describe where energy is held, while transfer pathways describe how energy moves.
• Every energy transfer can be analyzed by identifying the starting store, the transfer pathway, and the final store(s).
• Energy flow diagrams provide a clear way to represent these transfers.
• The principle of conservation of energy states that energy is never created or destroyed—it is simply transferred from one store to another.

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Suggested Images

1. Energy Stores and Transfer Pathways Concept Map ⭐

A concept map with two main branches:

Energy Stores

• Kinetic
• Gravitational potential
• Chemical
• Elastic
• Nuclear
• Electrostatic
• Internal

Transfer Pathways

• Mechanical work
• Electrical work
• Heating
• Waves

Use arrows to emphasize that stores hold energy, while pathways move energy.

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2. Everyday Energy Transfer Examples

A four-panel infographic showing:

• Person lifting a box → Mechanical work.
• Battery powering a torch → Electrical work.
• Pot heating on a stove → Heating.
• Sun warming Earth → Waves.

Include arrows from the initial store, through the transfer pathway, to the final store.

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3. Energy Flow Diagram Examples

Three simple flow diagrams:

• Roller coaster.
• Flashlight.
• Electric kettle.

Each should clearly label:

• Initial energy store.
• Transfer pathway.
• Final energy store(s).

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4. Conservation of Energy

A flowchart showing energy being transferred through several stores and pathways while emphasizing:

Total Energy Before = Total Energy After

Include examples of useful and dissipated energy transfers.

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5. Energy Transfer Pathways in a House

A cutaway illustration of a house showing:

• Electrical energy powering lights and appliances.
• Heating warming rooms.
• Mechanical work from a washing machine or fan.
• Waves from Wi-Fi, radio, or sunlight entering through windows.

Label each transfer pathway to connect the concepts with everyday life.