1.7.1Motion, Forces and Energy
Energy Stores and Transfers — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions
5 min read 9 parts Lesson 64 of 91 1 quiz
Lesson summary
1.7.1 Energy Stores and Transfers — IGCSE PHYSICS notes: Name the main energy stores and transfer pathways and describe energy changes in everyday situations.Energy = what allows work to be done and changes to occur, measured in joules (J).Energy is never used up — it moves betwe…
- Gravitational potential
- Elastic (strain)
- Thermal (internal)
- Electrostatic and magnetic
- Mechanical work
- Electrical work
Part 1 of 7Energy stored and moved
Energy
Energy what allows work to be done and changes to occur, measured in joules (J).
Energy is never used up
- Energy is never used up it moves between stores or between objects.
The total energy stays the same.
Energy is a scalar, with size but no direction.
Part 2 of 7The main energy stores
The main energy stores
Kinetic
- Kinetic a moving object such as a running person or a car.
Gravitational potential
- Gravitational potential an object raised above the ground, such as water in a high reservoir or a book on a shelf.
Elastic (strain)
- Elastic (strain) a stretched or compressed object such as a spring, elastic band or bent ruler.
Chemical
- Chemical fuels, food and batteries, released in chemical reactions.
Thermal (internal)
- Thermal (internal) the random kinetic and potential energy of the particles of an object, larger for hotter objects.
Nuclear
- Nuclear energy in the nuclei of atoms, released in fission and fusion.
Electrostatic and magnetic
- Electrostatic and magnetic energy of charges or magnets in fields, as in a charged capacitor or two magnets pushed together.
Part 3 of 7Energy transfer pathways
1Mechanical work
- Mechanical work a force moves an object through a distance, as in pushing a box or friction slowing a car.
2Electrical work
- Electrical work a current carries energy, as when a battery powers a bulb or motor.
3Heating
- Heating energy moves from hotter to colder places by conduction, convection or radiation.
4Waves (radiation)
- Waves (radiation) light, sound or other waves carry energy from a source to a receiver.
Part 4 of 7Examples of energy changes
| Device | Store decreasing | Pathway | Useful store increasing |
|---|---|---|---|
| Electric kettle | Electrical supply | Electrical work, then heating | Thermal store of water |
| Falling ball | Gravitational potential | Mechanical work | Kinetic |
| Loudspeaker | Electrical | Electrical work, then sound waves | Sound waves |
| Released catapult | Elastic | Mechanical work | Kinetic |
| Nuclear power station | Nuclear | Heating, then work, then electrical | Electrical energy to the grid |
Part 5 of 7Systems and the stores to learn
1System
System an object or group of objects being observed.
- Defining the system sets the starting point and stopping point for the energy transfers considered.
2
Energy is transferred only when something changes within a system.
- An apple on a table has no transfer, but when the table is removed the apple falls and energy is transferred.
3Seven stores
- Seven stores kinetic, gravitational potential, chemical, elastic (strain), nuclear, electrostatic and internal (thermal).
4
Electrical, light and sound are not stores; they are transfer pathways.
5Energy flow diagrams
- Energy flow diagrams they show stores in boxes and pathways as arrows, with total energy in equal to total energy out.
Part 6 of 7Describing an energy change
Pushing a trolley
- Pushing a trolley the chemical store in the muscles decreases, work is done and the kinetic store of the trolley increases.
Name the store that starts with the energy, the pathway and the store that ends with it.
In almost every device some energy goes to the thermal store of the surroundings.
- This wasted energy spreads out and is difficult to use again.
Check that energy in equals useful energy out plus wasted energy out.
Part 7 of 7More from the specification
1Quantitative energy transformation
- Quantitative energy transformation tracking mechanical work and heat pathways provides a rigorous means to verify energy conservation across closed systems.
2Principle of Conservation of Energy
- Energy cannot be created or destroyed, only transferred between different stores,
- meaning the total energy input to any closed system always equals the total energy output.
3Kinetic Energy Calculation
- The amount of energy stored in an object's kinetic store depends on its mass and speed, calculated using the standard equation Ek = 1/2 m v2 .
- (measured in Joules, J)
4Gravitational Potential Energy
- The amount of energy transferred to a gravitational store when an object of mass m is raised through a vertical height h against gravity is given by ΔEp = m g Δh.
5Energy Efficiency and Sankey Diagrams
- Efficiency is calculated as × 100%,
- (useful energy output / total energy input)
- and can be visually represented using a Sankey diagram where arrow width is proportional to the amount of energy transferred.
6Principle of Conservation of Energy
- Energy cannot be created or destroyed, only transferred between different stores,
- meaning the total energy input to any closed system always equals the total energy output.
7Kinetic Energy Calculation
- The amount of energy stored in an object's kinetic store depends on its mass and speed, calculated using the standard equation Ek = 1/2 m v2 .
- (measured in Joules, J)
8Gravitational Potential Energy
- The amount of energy transferred to a gravitational store when an object of mass m is raised through a vertical height h against gravity is given by ΔEp = m g Δh.
9Energy Efficiency and Sankey Diagrams
- Efficiency is calculated as × 100%,
- (useful energy output / total energy input)
- and can be visually represented using a Sankey diagram where arrow width is proportional to the amount of energy transferred.
10Efficiency
- Useful output divided by total input.
Key terms
| Term | Meaning |
|---|---|
| Joule (J) | SI unit of energy and work. |
| Energy store | A way in which energy is held, such as kinetic or chemical. |
| Energy transfer | Movement of energy from one store to another. |
| Thermal energy store | Total random kinetic and potential energy of the particles of an object. |
| Wasted energy | Energy transferred to stores that are not useful, usually thermal in the surroundings. |
| Pathway | Mechanism of transfer: work, heating, electrical or waves. |
Avoid these mistakes
1
Saying energy is used up or lost — it is transferred, and the wasted part goes to the thermal store of the surroundings.
2
Calling heat a store — heat is a transfer pathway; the store is thermal (internal) energy.
3
Saying a moving object has force — it has kinetic energy.
4
Mixing up stores and pathways — work, heating, electrical work and waves are pathways.
5
Thinking energy is a vector — it is a scalar.
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