Energy is held in stores

You never "use energy up" — you shift it from one store to another. Eduqas names seven energy stores:

Watch out: "heat", "electrical", "light" and "sound" are not stores — they are transfer pathways. We'll meet those next.

Which store?

Four ways energy moves

The Eduqas spec lists four methods of transferring energy between stores:

• Mechanical work — a force moves an object (pushing, lifting, stretching).
• Electrical work — charge moves through a potential difference.
• Heating — energy passes from a hotter to a cooler object.
• Radiation — e.g. light, infrared or sound carrying energy away.

Name the pathway

Tap the pathway that does the main energy transfer in each case.

Kinetic energy store

Every moving object has energy in its kinetic store. It depends on mass and, much more strongly, on speed:

Because velocity is squared, tripling the speed gives nine times the kinetic energy — a key reason braking distances grow so fast.

Your turn — kinetic energy

Gravitational potential store

Raise an object and you fill its gravitational store. A change in elevation is a form of mechanical work:

Your turn — gravitational store

Elastic potential store

Stretch or squash a spring (within its limit of proportionality) and you fill its elastic potential store. Deformation is a form of mechanical work:

x is the extension (how much longer the spring gets), not the total length. Like kinetic energy, the extension is squared. The spring force itself is given by F = k x.

Your turn — elastic store

Energy is never lost

The law of conservation of energy: energy cannot be created or destroyed — only transferred between stores, stored, or dissipated.

On a playground swing, energy moves between the gravitational store (at the top) and the kinetic store (at the bottom):

In a perfect (closed) system the totals always balance: g.p.e. lost = k.e. gained. In real life a little is dissipated by air resistance and friction — warming the surroundings.

Reading the swing

Specific heat capacity

To warm something up you fill its thermal store. How much energy that takes depends on the material's specific heat capacity, c:

The specific heat capacity is the energy needed to raise 1 kg of a substance by 1 °C (without a change of state). Water's is high (4200 J/kg°C), which is why it is slow to heat and slow to cool — handy for central heating.

Measuring c: heat a known mass of a metal block with an electric immersion heater, record the energy supplied and the temperature rise, then calculate c = Q ÷ (m ΔT).

Your turn — heating a metal block

Changing state

When a substance changes state (melts or boils) its temperature does not change, even though energy is still being transferred. The energy goes into breaking bonds between particles. This is described by the specific latent heat, L:

Higher tier only. Specific latent heat is the energy needed to change the state of 1 kg of a substance with no change in temperature. There is one value for melting (fusion) and a different value for boiling (vaporisation).

Your turn — latent heat

Power is the rate of transfer

Power tells you how quickly energy is transferred (or how quickly work is done):

One watt is one joule per second (1 W = 1 J/s). A 1800 W microwave and a 900 W microwave heat the same meal — but the 1800 W one gets there in half the time.

Your turn — power

Useful vs wasted energy

In every transfer, some energy is dissipated — spread out to the surroundings (usually by heating) where it is no longer useful. A Sankey diagram shows this: the wider the arrow, the more energy.

That motor's efficiency = 375 ÷ 500 = 0.75 = 75%. Reducing wasted heat would push the efficiency higher.

Your turn — efficiency

Wasting less energy

• Lubrication — oil between moving parts cuts friction, so less energy is dissipated by heating.
• Thermal insulation — loft insulation and cavity-wall insulation trap pockets of air, slowing conduction and convection.
• Double glazing — a layer of trapped air (or a vacuum) between two panes nearly stops conduction through windows.
• A wall loses energy more slowly when it is thicker and made of a material with a lower thermal conductivity.

Keeping the heat in

Where our energy comes from

Over the last 200 years demand for electricity has grown enormously. The big divide is renewable (replaced as fast as it's used) vs non-renewable (a finite store):

Trade-offs: fossil fuels (coal, oil, gas) are reliable and release a lot of energy, but emit CO₂ and other greenhouse gases. Nuclear fuel emits no CO₂ and is very energy-dense, but leaves long-lived radioactive waste. Many renewables (solar, wind, waves) are less reliable — they depend on weather or daylight. Biomass is renewable but still releases CO₂ when burned.

Renewable or not?

Tap a source, then tap the box it belongs in.

Choosing a source

The equations to know

You've covered all of Eduqas Topic 1 — energy changes in a system & the ways energy is stored, conservation & dissipation, national & global energy sources, and energy transfers. Press Finish to see your score.