Energy stores and systems (AQA GCSE Physics): Revision Notes
Energy stores and systems
What is a system?
A system can be one object or several objects working together. When a system changes, the way energy is stored changes too.
Understanding Systems Through Examples
When you throw a ball up in the air, the ball is a system that changes as it moves. As the ball rises, its energy stores change from kinetic energy (movement) to gravitational potential energy (height), demonstrating how systems can transform energy from one store to another.
The eight main energy stores
Energy can be stored in eight different ways:
- Chemical - stored in things like fuel, food, and batteries
- Kinetic - energy that moving objects have
- Gravitational potential - energy that raised objects have (like a book on a shelf)
- Elastic - energy stored in stretched or squashed springs
- Thermal - energy that hot objects have
- Magnetic - energy between two magnets
- Electrostatic - energy between two electric charges
- Nuclear - energy stored in nuclear fuel
These eight energy stores are fundamental to understanding how energy exists in different forms throughout the universe. Every energy transfer you observe involves moving energy between these stores.
Conservation of energy
This is one of the most important rules in physics:
The Law of Conservation of Energy
Energy can move from one store to another, but it cannot be created or destroyed. The total amount of energy in a closed system stays exactly the same.
A closed system means no energy can flow in or out of the system.
Some energy often gets wasted as heat to the surroundings, but the total energy is still the same.
How energy transfers happen
Energy moves between stores in three main ways:
The Three Methods of Energy Transfer
- By heating - when hot objects warm up cooler objects
- Through forces - when forces make objects move
- By electric current - when electricity flows through circuits
Understanding these transfer methods helps explain how energy moves in everyday situations and complex systems.
Examples of energy transfers in action
Here are five common examples you should know:
Worked Example: Throwing a Ball Upwards
Kinetic energy changes to gravitational potential energy as the ball slows down and rises.
What happens:
- Initially: Ball has maximum kinetic energy (moving fast)
- As it rises: Kinetic energy decreases, gravitational potential energy increases
- At the peak: Maximum gravitational potential energy, zero kinetic energy
Worked Example: Ball Hitting an Obstacle
Kinetic energy changes to thermal energy (heat) and sometimes sound.
What happens:
- Before impact: Ball has kinetic energy due to motion
- During impact: Kinetic energy transfers to thermal energy and sound energy
- After impact: Ball has less kinetic energy, surroundings are slightly warmer
Additional examples include:
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Accelerating an object - when a force speeds something up, its kinetic energy increases
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Car brakes - kinetic energy changes to thermal energy because of friction in the brakes
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Boiling a kettle - electrical energy changes to thermal energy to heat the water
Energy Waste in Transfers
In all these examples, some energy gets wasted as heat to the surroundings. This doesn't mean energy is destroyed - it just means some energy transfers to thermal energy stores in the environment, making it less useful for the intended purpose.
Energy flow diagrams
Scientists use flow diagrams to show how energy moves between stores. These diagrams use arrows to show:
- Which energy store the energy starts in
- Which energy store it moves to
- How the transfer happens
Example Energy Flow Diagram
In a battery-powered fan:
- Chemical energy in the battery transfers by electric current to kinetic energy in the moving fan
- Some energy also becomes thermal energy in the surroundings
The diagram would show: Chemical → (by electric current) → Kinetic + Thermal
Remember!
Key Points to Remember:
- A system is one or more objects that can change
- There are eight main energy stores - chemical, kinetic, gravitational potential, elastic, thermal, magnetic, electrostatic, and nuclear
- Energy cannot be created or destroyed - it can only move between different stores
- Energy transfers happen through heating, forces, or electric current
- Some energy usually gets wasted as heat to the surroundings