Conservation of energy — Edexcel GCSE Combined Science

Conservation of energy is a fundamental principle in physics stating that energy cannot be created or destroyed, only transferred from one store to another. In the Edexcel GCSE Combined Science course, this topic explores how energy is stored (e.g., kinetic, gravitational potential, thermal, chemical) and how it flows between stores during processes like falling, braking, or electrical heating. Understanding this principle allows you to predict how much energy is usefully transferred and how much is 'wasted' to the surroundings, often as heat or sound.

This topic is crucial because it underpins all of physics and engineering. For example, when you lift a book, you do work to increase its gravitational potential energy; when it falls, that energy converts to kinetic energy. In real-world applications, engineers aim to maximise efficiency by reducing wasted energy. The law of conservation of energy also links to the idea that the total energy before and after any event is the same, which is a key concept for solving problems involving energy transfers and efficiency calculations.

In the wider Combined Science curriculum, conservation of energy connects to topics like forces (work done), electricity (energy in circuits), and waves (energy transfer). It also lays the groundwork for more advanced concepts in physics, such as thermodynamics and renewable energy. By mastering this topic, you'll be able to analyse everyday situations—from a bouncing ball to a car braking—and calculate energy changes using equations like Ek = ½mv² and Ep = mgh.

• →The law of conservation of energy: total energy in a closed system remains constant; energy is transferred between stores, not created or destroyed.
• →Energy stores: kinetic (movement), gravitational potential (height), elastic potential (stretched/compressed), thermal (temperature), chemical (bonds), nuclear, and electrostatic.
• →Energy transfers: mechanically (by forces), electrically (by current), by heating (conduction, convection, radiation), and by radiation (light/sound).
• →Efficiency = useful output energy ÷ total input energy (as a decimal or percentage); wasted energy is dissipated to the thermal store of the surroundings.
• →Work done = force × distance (W = Fd) and is equal to the energy transferred when a force moves an object.

• Correct identification of energy stores (e.g., kinetic, gravitational potential, chemical, thermal).
• Application of the law of conservation of energy in closed systems.
• Correct use of the GPE equation (delta GPE = m x g x delta h).
• Correct use of the kinetic energy equation (KE = 0.5 x m x v^2).
• Calculation of efficiency using the ratio of useful energy transferred to total energy supplied.
• Explanation of energy dissipation and how mechanical processes become wasteful through heating.
• Description of methods to reduce unwanted energy transfer, such as lubrication and thermal insulation.

• 💡Always state the formula being used before substituting values.
• 💡Ensure all units are in SI units (e.g., mass in kg, height in m, speed in m/s) before calculating.
• 💡When asked about energy dissipation, always mention that energy is transferred to the thermal store of the surroundings.
• 💡Use the term 'dissipated' rather than 'lost' when describing energy transfers to the surroundings.
• 💡Check if the question asks for an answer to a specific number of significant figures.
• 💡Always state the energy stores before and after a transfer. For example: 'The ball has gravitational potential energy at the top, which is transferred to kinetic energy as it falls.' This shows clear understanding.
• 💡When calculating efficiency, check if the question asks for a decimal or percentage. Show your working and include units (Joules for energy).
• 💡Remember that 'wasted' energy is not destroyed—it is transferred to less useful stores, usually thermal energy of the surroundings. Use the phrase 'dissipated to the surroundings' to gain marks.

• Confusing energy stores with energy transfers.
• Failing to convert units (e.g., grams to kilograms) before using energy equations.
• Incorrectly identifying a system as 'closed' when energy is being dissipated to the surroundings.
• Misinterpreting the efficiency formula by swapping the numerator and denominator.
• Forgetting to square the velocity in the kinetic energy equation.
• Misconception: Energy is 'used up' or 'lost'. Correction: Energy is never lost; it is transferred to other stores, often as thermal energy in the surroundings (dissipated).
• Misconception: Kinetic energy is always conserved in collisions. Correction: In inelastic collisions, some kinetic energy is transferred to thermal and sound stores; total energy is conserved, but kinetic energy may not be.
• Misconception: Efficiency can be greater than 100%. Correction: Efficiency is always ≤ 1 (or ≤ 100%) because useful output energy cannot exceed total input energy due to conservation of energy.