Energy Stores and Conservation

Energy never disappears - it just moves around or changes form, which is called the law of conservation of energy. You'll measure energy in Joules (J), and there are several key energy stores you need to know.

Kinetic energy is the energy of moving objects, calculated using E = ½mv². Gravitational potential energy (GPE) is stored energy due to height, found with E = mgh. Elastic potential energy exists in stretched or compressed springs using E = ½ke².

Don't forget that sound and vibrational energy are actually forms of kinetic energy, whilst fuels, food, and batteries store chemical potential energy. Thermal energy relates to temperature changes and uses the equation ΔE = mcΔT.

Quick tip: In closed systems (no energy lost to surroundings), you can equate different energy stores - like GPE at the top equals KE at the bottom for a falling object!

Measuring Specific Heat Capacity and Power

Specific heat capacity (SHC) tells you how much energy is needed to raise 1kg of a substance by 1°C. The practical to measure this involves heating a metal block or water whilst carefully monitoring temperature changes.

You'll measure the mass using a top-pan balance, then use an electrical heater whilst recording voltage and current. After a set time, you calculate the temperature change and work out the power supplied using P = VI, then energy supplied using E = Pt.

Finally, rearrange the SHC equation $c = ΔE/mΔT$ to find your answer. Remember that some energy always escapes to the surroundings, so your calculated SHC will likely be higher than the actual value.

Power measures the rate of energy transfer and is measured in Watts (W). This connects energy and time, showing how quickly energy changes happen in different situations.

Exam focus: Practice rearranging these equations - examiners love testing whether you can manipulate the formulas to find different variables!