1. Energy stores and systems
1 Energy Topic overview
Energy stores and systems
A system is an object or group of objects. When a system changes, the way energy is stored changes.
Types of energy stores:
Chemical
Gravitational potential
Thermal
Electrostatic
Kinetic
Elastic potential
Magnetic
Nuclear
Energy is measured in joules, J.
© Hodder & Stoughton 2016

2. Changes in kinetic energy
1 Energy Topic overview
Changes in kinetic energy
The energy stored by a moving object can be calculated using:
kinetic energy=0.5×mass× (speed) 2
𝐸 𝑘 = 1 2 𝑚 𝑣 2
Kinetic energy [𝐸𝑘] is measured in joules, J.
Mass [m] is in kilograms, kg.
Speed [v] is in metres per second, m/s.
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3. Changes in elastic potential energy
1 Energy Topic overview
Changes in elastic potential energy
The energy stored in a stretched spring can be calculated using:
elastic potential energy=0.5×spring constant× (extension) 2
𝐸 𝑒 = 1 2 𝑘 𝑒 2
Elastic potential energy [𝐸e] is measured in joules, J.
Spring constant [k] is in newtons per metre, N/m.
Extension [e] is in metres, m.
© Hodder & Stoughton 2016

4. Changes in gravitational potential energy
1 Energy Topic overview
Changes in gravitational potential energy
The energy gained by an object raised above the ground can be calculated using:
gravitational potential energy=mass×gravitational field strength×height
𝐸 𝑝 =𝑚𝑔ℎ
Gravitational potential energy [𝐸p] is measured in joules, J.
Mass[m] is in kilograms, kg.
Gravitational field strength [g] is in newtons per kilogram, N/kg.
Height [h] is in metres, m.
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5. Energy changes in systems
1 Energy Topic overview
Energy changes in systems
The amount of energy stored or released from a system, as its temperature changes, can be calculated using the equation:
change in thermal energy=mass×specific heat capacity×temperature change
∆𝐸=𝑚𝑐∆𝜃
Change in thermal energy [ΔE] is measured in joules, J.
Mass[m] is in kilograms, kg.
Specific heat capacity[c] is in joules per kilogram per degree Celsius, J/Kg °C.
Temperature change [Δ𝜃] is in degrees Celsius, °C.
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6. Power 1 Energy Topic overview OR Power is measured in watts, W.
power = energy transferred time taken
𝑃= 𝐸 𝑡 OR
𝑃= 𝑊 𝑡
power = work done time taken
Power is measured in watts, W.
Energy transferred is in joules, J.
Time taken is in seconds, s.
Work done is in joules, J.
© Hodder & Stoughton 2016

7. Energy transfers in a system
1 Energy Topic overview
Energy transfers in a system
Energy can be transferred usefully, stored or ‘wasted’, but cannot be created or destroyed.
People are always trying to find ways to waste (or dissipate) less energy, whether in industry or around the home.
© Hodder & Stoughton 2016

8. Efficiency 1 Energy Topic overview
The energy efficiency for all energy transfers can be calculated using:
efficiency = useful output energy transfer total input energy transfer (×100%) OR
efficiency = useful power output total power input (× 100%)
© Hodder & Stoughton 2016

9. National and global energy resources
1 Energy Topic overview
National and global energy resources
Fossil fuels, such as coal, oil and gas, are non-renewable sources of energy.
Renewable energy sources include the Sun, tides, the wind and waves.
The three main uses of energy resources are: transport, heating and electricity.
© Hodder & Stoughton 2016