Understanding Energy in Physics - AQA Topic Guide

Energy Stores and Conservation

Here's something that might blow your mind: energy can never be created or destroyed. It just moves around and changes form, like a cosmic game of pass-the-parcel that's been going on since the universe began.

You'll encounter several key types of energy stores. Kinetic energy $E = ½mv²$ is the energy of moving objects - think of a football flying towards goal. Gravitational potential energy $E = mgh$ is stored energy that objects have because of their height - like water sitting behind a dam. Elastic potential energy $E = ½ke²$ is what you get when you stretch or compress something springy.

Don't forget about thermal energy, which relates to temperature changes and uses the formula ΔE = mcΔT. Sound is actually just another form of kinetic energy, whilst batteries, food, and fuels all contain chemical potential energy waiting to be released.

Quick Check: Remember that all energy is measured in Joules (J) - this will come up constantly in your calculations!

Energy Transfers, Power and Efficiency

Energy loves to move around within systems (objects or groups of objects). When you drop something, gravitational potential energy transforms into kinetic energy as it falls. In a closed system, no energy escapes to the surroundings - though in real life, some energy usually does leak out.

Power measures how quickly energy transfers happen, using the formula P = E/t and measured in Watts (W). Think of it as energy's speedometer - a 100W light bulb transfers energy twice as fast as a 50W bulb.

Efficiency tells you how much useful energy you actually get out compared to what you put in. Most energy transfers waste some energy as heat - that's why your laptop gets warm and why buildings lose thermal energy through conduction in walls, windows, and roofs. Smart solutions like cavity walls and double glazing help reduce these losses.

We get energy from finite sources like fossil fuels and nuclear materials (which will eventually run out) or renewable sources like wind, solar, and hydroelectric power that naturally replenish themselves.

Pro Tip: Efficiency = (Useful energy out ÷ Total energy in) × 100 for percentage - this formula appears in loads of exam questions!