GCSE Physics energy

By The STEM-Tutor team · Updated October 2026

Energy is the first topic in many GCSE Physics courses and links to almost everything else. Here are the key ideas.

Energy stores and transfers

Energy is stored in different ways: kinetic, gravitational potential, elastic potential, thermal, chemical, nuclear and more. Energy is transferred between stores by forces doing work, by electrical work, by heating and by radiation.

Conservation of energy

Energy cannot be created or destroyed, only transferred between stores. In a closed system, the total energy stays the same.

Key equations

• Kinetic energy: E_k = ½mv²
• Gravitational potential energy: E_p = mgh
• Elastic potential energy: E_e = ½ke²
• Thermal energy: ΔE = mcΔθ
• Power: P = E/t

Efficiency

Efficiency = useful energy output ÷ total energy input. Wasted energy usually ends up as thermal energy in the surroundings. Lubrication and insulation reduce unwanted transfers.

Energy resources

• Non-renewable: coal, oil, gas and nuclear fuel.
• Renewable: wind, solar, hydroelectric, tides, waves, geothermal and biofuels.

Exam questions often ask you to compare resources on reliability, cost and environmental impact.

Exam tips

1. Name the stores before and after a change.
2. Check units: mass in kg and speed in m/s.
3. Revise the specific heat capacity required practical.

Energy stores and pathways

GCSE Physics describes energy as being held in stores and moved between them by pathways. The main stores are kinetic, gravitational potential, elastic potential, thermal, chemical, magnetic, electrostatic and nuclear. Energy moves between stores by mechanical work, electrical work, heating, and radiation such as light or sound. When you describe a process, name the store energy leaves, the store it enters, and how it was transferred. For example, when a ball falls, energy moves from its gravitational store to its kinetic store by the work done by gravity.

Worked examples

Example 1: kinetic energy

Find the kinetic energy of a 1000 kg car moving at 20 m/s.

• E_k = ½mv² = ½ × 1000 × 400 = 200 000 J, or 200 kJ.

Example 2: gravitational potential energy

A 2 kg book is lifted onto a shelf 1.5 m high. Find the gain in GPE. (g = 9.8 N/kg)

• E_p = mgh = 2 × 9.8 × 1.5 = 29.4 J.

Example 3: energy conservation

A ball is dropped from 5 m. Find its speed just before it hits the ground, ignoring air resistance. (g = 9.8 N/kg)

• GPE lost = KE gained: mgh = ½mv², so v² = 2gh = 98.
• v ≈ 9.9 m/s. The mass cancels, so any ball dropped from 5 m lands at the same speed.

Example 4: efficiency

A motor uses 500 J of electrical energy and transfers 350 J to useful kinetic energy. Find its efficiency.

• Efficiency = useful output/total input = 350/500 = 0.7, or 70%.

Example 5: power

A crane lifts a load, doing 60 000 J of work in 20 s. Find its power.

• P = E/t = 60 000/20 = 3000 W.

Example 6: specific heat capacity

How much energy is needed to heat 2 kg of water by 10 °C? (c = 4200 J/kg °C)

• ΔE = mcΔθ = 2 × 4200 × 10 = 84 000 J.

Example 7: reading a Sankey diagram

A lamp takes in 100 J of electrical energy and gives out 20 J of light. The rest is wasted as heat. What is its efficiency?

• Efficiency = 20/100 = 20%. On a Sankey diagram, the width of each arrow shows the amount of energy.

Reducing wasted energy

Energy is never destroyed, but it can be wasted by spreading out into the surroundings, usually as thermal energy. To reduce unwanted transfers, use lubrication to reduce friction in machines, and thermal insulation to reduce heat loss from buildings. Cavity wall insulation, loft insulation and double glazing all trap air, which is a poor conductor. Thicker walls and materials with lower thermal conductivity also reduce the rate of heat loss.

Comparing energy resources

Renewable resources, such as wind, solar, hydroelectric, tidal, wave, geothermal and biofuels, will not run out. Non-renewable resources, such as coal, oil, gas and nuclear fuel, will. Fossil fuels are reliable and can respond quickly to demand, but they release carbon dioxide, which contributes to climate change. Wind and solar produce no carbon dioxide when running, but depend on the weather. Exam questions often ask you to compare two resources; give a fair advantage and disadvantage of each, linked to reliability, cost and environmental impact.

Common mistakes

• Saying energy is “used up”; it is transferred and often wasted, never destroyed.
• Forgetting to square the speed in kinetic energy.
• Giving efficiency greater than 100%, which is impossible.
• Using the wrong units: energy in joules, power in watts, mass in kg.

Practice questions

Try each one before opening the answer.

Frequently asked questions

What is the law of conservation of energy?

Energy cannot be created or destroyed. It can only be transferred from one store to another, so the total energy of a closed system stays the same.

What does specific heat capacity mean?

It is the energy needed to raise the temperature of 1 kg of a substance by 1 °C. Water has a high value, so it heats up and cools down slowly.

Key takeaways

• Energy moves between stores through pathways.
• Energy is conserved; wasted energy usually spreads out as heat.
• E_k = ½mv² and E_p = mgh.
• Efficiency = useful output ÷ total input.
• Compare energy resources on reliability, cost and environment.

Where to go next

Energy links to forces, electricity and the required practicals.

• GCSE Physics forces
• GCSE Physics electricity
• GCSE Physics equations

How to revise energy

Energy appears in almost every other topic, so it is worth making it secure early. Learn the equations for kinetic energy, gravitational potential energy, elastic potential energy, power and efficiency, and practise rearranging each one. Then practise describing energy transfers in words using stores and pathways. Many students lose marks by naming the wrong store, so be precise.

Energy in everyday life

Your electricity bill measures energy in kilowatt-hours. One kilowatt-hour is the energy a 1 kW appliance uses in one hour, which is 3.6 million joules. Choosing efficient appliances, such as LED bulbs instead of filament bulbs, reduces the energy wasted as heat and lowers the bill.

Seeing energy in the world around you, from kettles to cars, makes the ideas easier to remember.