Energy Stores and Systems

Your phone battery, a bouncing ball, and even your hot cup of tea all have one thing in common - they're storing energy in different ways. There are eight energy stores you need to master for your exams.

Thermal energy exists because of temperature, whilst kinetic energy appears when objects move. Gravitational potential energy builds up when you lift something high, and elastic potential energy gets stored in stretched springs or rubber bands.

The remaining four are chemical energy (found in food, fuel, and batteries), magnetic energy (between magnets), electrostatic energy (between charged objects), and nuclear energy (locked inside atoms). Once you recognise these stores, you'll start spotting them everywhere in exam questions.

Quick Tip: Think of energy stores like different bank accounts - energy moves between them but the total amount stays the same!

Energy Transfer Methods

Energy doesn't teleport between stores - it needs specific pathways to move around. There are four main transfer methods that crop up constantly in your physics papers.

Heating transfers energy from hot objects to cooler ones, like when a kettle's element warms up water. Doing work happens when forces move objects or when electrical current flows - think throwing a ball or a car accelerating.

Radiation moves energy through electromagnetic waves (like light warming your face), whilst electrical transfer occurs when current flows through circuits. Understanding these pathways helps you tackle energy problems systematically.

When objects fall, energy shifts from their gravitational potential energy store to their kinetic energy store. In reality, air resistance means some energy also transfers to thermal stores in the surrounding air.

Remember: A system can be a single object or multiple objects you're focusing on - energy can transfer into it, out of it, or between different parts within it.

Closed Systems and Energy Conservation

Here's the golden rule that'll save you marks in every energy question: the total energy in a closed system never changes. This means energy can't be created or destroyed, only moved around.

A closed system is one where neither matter nor energy can enter or leave - think of it like a sealed box. Even when dramatic changes happen inside, the total energy remains constant.

This principle helps you solve problems systematically. If a ball loses gravitational potential energy whilst falling, it must gain exactly the same amount of kinetic energy (ignoring air resistance). The numbers always balance out.

Exam Strategy: When stuck on energy questions, list what energy stores increase and decrease - they must equal each other!

Calculating Kinetic and Elastic Energy

Time for the maths bit - but don't worry, these equations are your friends once you practise them. Kinetic energy calculations pop up constantly, so memorise this formula: Ek = ½mv².

The equation tells you that doubling an object's speed actually quadruples its kinetic energy (because you're squaring the velocity). Mass matters too - heavier objects store more kinetic energy at the same speed.

For elastic potential energy, use Ee = ½ke². Here, 'k' represents the spring constant (how stiff the spring is), whilst 'e' shows how much you've stretched it. Stretch a spring twice as far, and you store four times more energy.

Gravitational potential energy uses the simpler formula Ep = mgh. This one's straightforward - more mass, greater height, or stronger gravity all mean more stored energy.

Calculator Tip: Watch out for that ½ in the kinetic and elastic energy equations - it's easy to forget under exam pressure!

Specific Heat Capacity

Different materials need different amounts of energy to heat up - this property is called specific heat capacity. Water needs loads of energy to warm up, which is why the sea stays cool in summer and warm in winter.

Specific heat capacity measures how much energy you need to raise 1kg of a substance by 1°C. Materials with high specific heat capacities are excellent for storing thermal energy - that's why water works brilliantly in central heating systems.

The formula ΔE = mcΔθ connects energy transfer to temperature changes. 'ΔE' represents energy change, 'm' is mass, 'c' is specific heat capacity, and 'Δθ' shows temperature change.

This equation works both ways - heating up and cooling down. When substances cool, they release exactly the same amount of energy they absorbed when warming up.

Real-world Connection: Metal car seats heat up quickly in summer (low specific heat capacity), whilst the plastic dashboard stays cooler (higher specific heat capacity).