Energy

Energy Stores

There are eight energy stores — ways that energy can be held within a system.

Being able to name and identify all eight stores is the foundation — every energy question starts here.

Energy Stores — Key Knowledge

Kinetic energy of a moving object
Gravitational potential energy due to height in a gravitational field
Elastic potential energy stored in a stretched/compressed object
Thermal energy related to temperature
Chemical energy stored in bonds — fuels, food, batteries
Magnetic energy due to magnets attracting/repelling
Electrostatic energy due to charged particles
Nuclear energy stored in the nucleus of an atom

Energy Transfers

Energy moves between stores by different transfer pathways.

Students must distinguish transfers (how energy moves) from stores (where energy sits).

Energy Transfers — Key Knowledge

Mechanically by a force acting on an object
Electrically by charges moving through a circuit
By heating due to a temperature difference
By radiation by electromagnetic waves or sound

Specific Heat Capacity

How hard it is to heat a material up. Measured as the energy needed to raise the temperature of 1 kg of a substance by 1°C.

Links thermal energy store changes to measurable quantities — essential for calculation questions.

Specific Heat Capacity — Key Knowledge

Specific heat capacity energy per kg per °C, units J/kg°C

ΔE = mcΔθ (energy change = mass × specific heat capacity × temperature change)

Work Done

When a force moves an object, energy is transferred. The amount of energy transferred is the work done.

Connects forces to energy transfers — if a force moves something, energy has been transferred.

Work Done — Key Knowledge

Work done energy transferred by a force, measured in joules, J

W = Fs (work done = force × distance)

Kinetic Energy

The energy in an object's kinetic energy store depends on its mass and speed.

Speed is squared — doubling speed quadruples kinetic energy.

Kinetic Energy — Key Knowledge

Kinetic energy energy of a moving object, measured in J

KE = ½mv² (kinetic energy = half × mass × speed²)

Gravitational Potential Energy

The energy stored when an object is raised in a gravitational field.

Directly linked to kinetic energy in falling/projectile questions — GPE lost = KE gained (if no dissipation).

Gravitational Potential Energy — Key Knowledge

Gravitational potential energy energy due to height, measured in J
Gravitational field strength g = 10 N/kg on Earth

GPE = mgh (gravitational potential energy = mass × gravitational field strength × height)

Elastic Potential Energy

The energy stored in a spring or elastic object when it is stretched or compressed.

Extension is squared — doubling extension quadruples the stored energy.

Elastic Potential Energy — Key Knowledge

Elastic potential energy energy in a deformed object, measured in J
Spring constant k, how stiff the spring is, measured in N/m

EPE = ½ke² (elastic potential energy = half × spring constant × extension²)

Power

Power is the rate of energy transfer — how fast energy is moved, measured in watts.

A more powerful device transfers the same energy in less time — links energy to time.

Power — Key Knowledge

Power rate of energy transfer, measured in watts, W
Watt 1 W = 1 joule per second

P = E/t (power = energy transferred ÷ time) or P = W/t (power = work done ÷ time)

Conservation and Dissipation

Energy cannot be created or destroyed — only transferred between stores. In every transfer, some energy is dissipated to the surroundings.

"Lost" energy isn't gone — it's been dissipated to thermal stores in the surroundings. Nothing is 100% efficient.

Conservation and Dissipation — Key Knowledge

Conservation of energy total energy in a closed system stays constant
Dissipation energy spreading out to surroundings, becoming less useful
Efficiency the proportion of energy usefully transferred, expressed as a decimal or percentage

Efficiency = useful output energy transfer ÷ total input energy transfer (or useful power output ÷ total power input)

Reducing Unwanted Transfers

Unwanted energy transfers can be reduced by design — making devices more efficient.

Common exam question — name a method and explain how it reduces energy waste in a named device.

Reducing Unwanted Transfers — Key Knowledge

Lubrication reduces friction between moving parts
Thermal insulation reduces energy transfer by heating
Thermal conductivity higher thermal conductivity = faster rate of energy transfer; thicker walls reduce cooling rate

Energy Resources

Energy resources are either renewable (won't run out) or non-renewable (finite supply). They're used for transport, electricity generation, and heating.

Renewable does not mean zero environmental impact — manufacturing, land use, and disposal all carry costs.

Energy Resources — Key Knowledge

Renewable replenished naturally — solar, wind, wave, tidal, hydroelectric, geothermal, bio-fuel
Non-renewable finite supply — fossil fuels: coal, oil, gas; nuclear fuel

Self-Assessment

Session Complete

Energy