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The law of conservation of energy says energy cannot be created or destroyed, only transferred from one store to another. Free GCSE Physics notes.
Energy Transfer and Conservation is part of Conservation and dissipation of energy in GCSE AQA Higher Physics.
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The law of conservation of energy says energy cannot be created or destroyed, only transferred from one store to another. Free GCSE Physics notes.
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Use this lesson to stay inside Conservation and dissipation of energy while connecting the detail back to the wider Energy topic.
Read the core explanations from Energy Transfer and Conservation before testing yourself from memory.
When you drop a ball, where does its energy go? It doesn't vanish into thin air. This is one of the most fundamental rules in physics: energy cannot be created or destroyed; it can only move from one place to another or change from one form to another. In real-world systems, factors such as friction and air resistance transform energy into forms that are less useful for performing work.
Think of energy like money in a bank account: although you can move it between different stores (just like transferring funds between accounts), the total amount remains constant. This analogy is intended to provide a helpful starting point for understanding energy conservation, and as your studies progress, you'll explore the many ways energy can change form.
A closed system is like a sealed box - nothing can get in or out. When we analyse energy in closed systems, we can track every joule of energy and see exactly where it goes.
Consider a bouncing ball in a sealed room. The ball starts with gravitational potential energy at the top. As it falls, this converts to kinetic energy. When it hits the floor, kinetic energy transfers to elastic potential energy as the ball compresses, then back to kinetic as it bounces up.
Worked example: Tracking Energy in a Bouncing Ball
A 0.5 kg ball is dropped from 2 m height. Calculate the energy at each stage (g = 10 N/kg).
Answer: Total energy remains 10 J throughout, just changing between different stores
Here's the catch: while energy is always conserved, it doesn't always stay useful. When you rub your hands together, kinetic energy transfers to thermal energy. The energy is still there, but it's spread out and much harder to use for doing work.
Every real energy transfer involves some dissipation. A car engine converts chemical energy from petrol into kinetic energy, but most of it dissipates as heat through the exhaust and radiator. The energy isn't lost - it's just no longer useful for moving the car.
Let's apply these principles to systems you encounter every day. Understanding where energy goes helps us design more efficient machines and reduce waste.
Worked example: Energy Analysis of a Mobile Phone Charger
A phone charger draws 10 W from the mains and delivers 8 W to the phone battery. Analyse the energy transfers.
Answer: Energy is conserved: 10 W input = 8 W useful output + 2 W waste heat
Energy questions appear in every physics exam. The key is systematic thinking: identify the system, track the energy stores, and always check your answer makes sense.
Common exam mistakes include forgetting that energy is conserved (not lost), mixing up energy and power, and not identifying all the energy stores in a system. Practice identifying where energy goes in everyday situations.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
The law of conservation of energy states that energy cannot be created or destroyed, only transferred from one store to another or transformed from one form to another. The total energy in a closed system remains constant.
A closed system is a system where no matter can enter or leave, allowing all energy transfers within the system boundaries to be tracked. The total energy in a closed system remains constant, like a sealed box where nothing can get in or out.
Energy cannot be created or destroyed; it can only be transferred from one store to another or transformed from one form to another. This is the principle of conservation of energy, and the total energy in a closed system remains constant.
Energy dissipation is the spreading out of energy to the surroundings, usually as thermal energy, making it less useful for doing work. It is often described as 'wasted' energy: a car engine dissipates most of its energy as heat through the exhaust and radiator.
Wasted energy is energy that spreads out to the surroundings, usually as thermal energy, making it less useful for doing work. This spreading out is called energy dissipation, and every real energy transfer involves some.
Wasted energy = input energy − useful output energy. A phone charger drawing 10 W from the mains and delivering 8 W to the battery wastes 10 − 8 = 2 W, which dissipates as heat, so input equals useful output plus waste.
Energy transfer means energy moving from one store to another, or changing from one form to another. Energy cannot be created or destroyed, so in a closed system the total energy stays constant while it moves between stores such as gravitational potential, kinetic and elastic potential.
A bouncing ball starts with gravitational potential energy, which converts to kinetic energy as it falls, then to elastic potential energy as it compresses on the floor, then back to kinetic as it bounces up. A 0.5 kg ball dropped from 2 m keeps a total of 10 J throughout.
A phone charger that draws 10 W from the mains and delivers 8 W to the phone battery dissipates the other 2 W as heat in the charger. Energy is conserved, because the 10 W input equals the 8 W useful output plus the 2 W waste.
Wasted energy is not lost; it is dissipated. The energy is still there but spread out to the surroundings, usually as thermal energy, so it is much harder to use for doing work. In a car engine, energy that dissipates as heat is no longer useful for moving the car.
When hands rub together, they transfer kinetic energy to thermal energy. The energy is still there, but it is spread out and much harder to use for doing work, which is an example of energy dissipation.
A car engine converts chemical energy from petrol into kinetic energy, but most of it dissipates as heat through the exhaust and radiator. That energy is not lost; it is just no longer useful for moving the car.
Friction and air resistance transform energy into forms that are less useful for performing work. The total energy is still conserved, but some of it is dissipated to the surroundings, usually as thermal energy.
When a dropped ball hits the floor, its kinetic energy transfers to elastic potential energy as the ball compresses, then back to kinetic energy as it bounces up. For a 0.5 kg ball dropped from 2 m, the total stays 10 J at every stage.
Common mistakes in energy conservation questions include forgetting that energy is conserved, not lost, mixing up energy and power, and not identifying all the energy stores in a system. Good answers identify the system, track the energy stores and check the total makes sense.