GCSE Energy Revision 🔋

🔋 Energy Stores

Energy doesn't disappear — it just moves between stores. There are 8 types.

💬 "Energy is like money. You can't create it from nothing. You can't destroy it. You can only move it around — usually into heat, which is the universe's way of wasting your pocket change."

💨

Kinetic

🏔️

Gravitational

🌡️

Thermal

⚗️

Chemical

🏹

Elastic

☢️

Nuclear

🔌

Electrostatic

🔊

Sound (wave)

👆 Click any energy store to see examples and exam tips

The golden rule: Energy is conserved — it can never be created or destroyed. It only transfers between stores. In every exam question, energy in = energy out (some useful, some wasted as heat).

⚡ Energy Transfers

Energy moves between stores in four ways. Know the name for each pathway.

💬 "A kettle transfers chemical energy (electricity from the grid) to thermal energy (hot water) to… making tea. The universe supports this use of energy."

🔧 Mechanically
A force moves through a distance. Work done transfers energy.

⚡ Electrically
Charge moving through a circuit. Very efficient transfer method.

🌡️ By heating
Thermal energy moves from hot to cold. Conduction, convection, radiation.

🌊 By radiation
EM waves (light, infrared, radio) or sound waves carry energy.

💨 Kinetic Energy — KE = ½mv²

Moving things have energy. The faster you go, the MUCH more energy you have — because of v².

💬 "Doubling your speed doesn't double your KE — it QUADRUPLES it. This is why 60 mph crashes are 4× worse than 30 mph crashes. v² is not messing around."

KE = ½ × m × v²

Kinetic energy (J) = half × mass (kg) × speed² (m/s)²

800Mass (kg)

15Speed (m/s)

90kKE (J)

Mass (kg): 800

Speed (m/s): 15

⚠️ Most common exam mistake: Forgetting to square the velocity. KE = ½ × m × (v²) not ½ × m × v.
Do v² first, then multiply by ½m.

🏔️ Gravitational Potential Energy — GPE = mgh

Height means stored energy. The higher something is, the more energy it has waiting to be released.

💬 "A boulder at the top of a hill has a lot of GPE and absolutely no chill. Give it a nudge and all that stored energy becomes kinetic very quickly."

GPE = m × g × h

Gravitational PE (J) = mass (kg) × 9.8 (N/kg) × height (m)

Mass (kg): 60

Height (m): 10

5880 J Gravitational PE

🎢 Conservation of Energy — GPE ↔ KE

When something falls, GPE converts to KE. Total energy stays constant (if no friction).

💬 "A roller coaster doesn't have an engine after the first hill. All those loops and drops? That's just GPE and KE swapping back and forth. The only thing slowing it down is friction — and the screaming."

GPE lost = KE gained (no friction)

mgh = ½mv² → v = √(2gh)

Friction: 0% (0% = frictionless, energy lost to heat as % increases)

⏱️ Power — P = E ÷ t

Power is how quickly energy is transferred. 1 Watt = 1 Joule per second.

💬 "A 2000W kettle transfers 2000 joules of energy every second. A phone charger is about 5W. The kettle is 400× more powerful. Both make your electricity bill cry."

P = E ÷ t

Power (W) = Energy (J) ÷ Time (s)

E = P × t

Energy (J) = Power (W) × Time (s)

Time: 60 seconds ()

♻️ Efficiency

No machine is 100% efficient. Some energy always escapes as heat. Always.

💬 "An old incandescent light bulb is about 5% efficient. 95% of its energy becomes heat. It's technically a heater that also makes light. Scientists called it a 'waste'. Marketing called it 'cosy'."

Efficiency = (useful ÷ total) × 100%

Wasted = Total − Useful

Efficiency: 75%

Total input energy: 1000 J

750Useful (J)

250Wasted (J)

75%Efficiency

🌡️ Specific Heat Capacity — E = mcΔT

Different materials need different amounts of energy to warm up. Water is unusually stubborn about it.

💬 "Water has a specific heat capacity of 4200 J/kg°C — one of the highest of any liquid. This is why the sea takes so long to warm up in summer and why your radiators work. Water is basically a thermal battery."

E = m × c × ΔT

Energy (J) = mass (kg) × specific heat capacity (J/kg°C) × temperature change (°C)

Mass (kg): 2

Temperature rise (°C): 50

420000 J Water needs

🌱 Energy Resources

Renewable = replenishes naturally. Non-renewable = runs out. Both have trade-offs.

💬 "Fossil fuels took 300 million years to form. We've used most of them in about 200 years. At least we were quick about it."

Renewable replenishes naturally Non-renewable finite supply

Source	Type	Advantages	Disadvantages
☀️ Solar	Renewable	Free, no emissions, low maintenance	Only works in daylight/sunshine, expensive panels
💨 Wind	Renewable	Free, no emissions, UK has lots of wind	Unreliable, noisy, visual impact
💧 Hydroelectric	Renewable	Reliable, no emissions, fast response	Floods valleys, disrupts ecosystems
🌊 Tidal	Renewable	Very reliable (tides are predictable), no emissions	High build cost, affects tidal habitats
🌋 Geothermal	Renewable	Reliable, low emissions, 24/7	Only viable in volcanic regions
🌿 Biofuel	Renewable	Carbon neutral (in theory), can replace petrol	Uses farmland, still produces CO₂
🛢️ Oil/Gas	Non-renewable	High energy density, reliable, existing infrastructure	CO₂ emissions, finite, oil spills
⛏️ Coal	Non-renewable	Abundant, cheap, reliable	Most CO₂ per unit energy, air pollution
☢️ Nuclear	Non-renewable	Huge output, very low CO₂, reliable	Radioactive waste, expensive, public concern

Exam tip: Questions often ask you to evaluate a resource for a specific context. Match the resource to the location and need — e.g. tidal for coastal UK, geothermal only for volcanic areas, nuclear for large baseload power.

✅ Quick Quiz

Five energy questions. Show what you know.

1. A 1000 kg roller coaster is at the top of a 40 m hill. g = 9.8 N/kg. What is its gravitational PE?

2. A motor has an input of 800 J and a useful output of 560 J. What is its efficiency?

3. A 500 W hair dryer runs for 3 minutes. How much energy is transferred?

4. Which energy store does a compressed spring have?

5. A 2 kg block of iron (c = 500 J/kg°C) is heated from 20°C to 70°C. How much energy is needed?

📋 Energy Equations

KE = ½mv²Kinetic energy — square v FIRST

GPE = mghg = 9.8 N/kg on Earth

P = E ÷ tPower (W) — time must be in seconds

E = P × tEnergy (J) — time in seconds

Eff = Eu÷Et × 100Efficiency % — always ≤ 100%

E = m × c × ΔTΔT = temperature CHANGE

W = F × dWork done (J) = force × distance

GCSE Energy 🔋