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2. Changes in Energy Systems (Energy as a Quantifiable Quantity Energy Stores (movement, temperature, position, chemical, elastic) Energy Transfers and Pathways Comparing Initial and Final Energy States Energy Increases and Decreases in Systems )
Year 8 • Physics
Changes in Energy Systems
This lesson explains how energy is measured, stored, transferred, and changed within systems. You will learn about energy stores, pathways, conservation of energy, and how to compare initial and final energy states.
Lesson Objectives
- Understand energy as a measurable quantity.
- Identify and describe different energy stores.
- Explain how energy is transferred using pathways.
- Compare initial and final energy states in systems.
- Describe energy increases, decreases, and wasted energy.
1. Energy as a Quantifiable Quantity
Energy is a quantifiable quantity, which means it can be measured, compared, and calculated.
Scientists measure energy to understand how systems change.
Key Facts:
• Energy is measured in joules (J)
• Larger values may be measured in kilojoules (kJ)
• Energy follows the law of conservation of energy
• Energy cannot be created or destroyed, only transferred or stored
• Energy is measured in joules (J)
• Larger values may be measured in kilojoules (kJ)
• Energy follows the law of conservation of energy
• Energy cannot be created or destroyed, only transferred or stored
2. Energy Stores
Energy is stored in different ways known as energy stores.
At KS3 level, you need to know these five main stores.
Kinetic (Movement)
Energy stored in moving objects. Faster movement means more kinetic energy.
Energy stored in moving objects. Faster movement means more kinetic energy.
Thermal (Temperature)
Energy stored in hot objects. Higher temperature means more thermal energy.
Energy stored in hot objects. Higher temperature means more thermal energy.
Gravitational Potential
Energy stored due to position or height above the ground.
Energy stored due to position or height above the ground.
Chemical
Energy stored in food, fuels, and batteries. Released during reactions.
Energy stored in food, fuels, and batteries. Released during reactions.
Elastic Potential
Energy stored when an object is stretched or squashed.
Energy stored when an object is stretched or squashed.
3. Energy Transfers and Pathways
Energy moves between stores using energy transfer pathways.
These pathways describe how energy is transferred.
Main Energy Transfer Pathways:
• Mechanical – energy transferred by forces
• Electrical – energy transferred by electric current
• Heating – energy transferred due to temperature difference
• Radiation – energy transferred by waves (infrared/light)
• Mechanical – energy transferred by forces
• Electrical – energy transferred by electric current
• Heating – energy transferred due to temperature difference
• Radiation – energy transferred by waves (infrared/light)
4. Initial and Final Energy States
A system is the object or group of objects being studied.
We compare energy stores before and after a change.
Initial energy state: Energy before a change happens
Final energy state: Energy after the change
Final energy state: Energy after the change
Example: A falling object changes gravitational potential energy into kinetic energy.
5. Energy Increases, Decreases and Wasted Energy
• Energy in a store increases when energy is transferred into it.
• Energy in a store decreases when energy is transferred out.
• Some energy is wasted as thermal energy to the surroundings.
• Wasted energy is not lost but becomes less useful.
• Energy in a store decreases when energy is transferred out.
• Some energy is wasted as thermal energy to the surroundings.
• Wasted energy is not lost but becomes less useful.
Practice Questions
A. Fill in the Blanks
- Energy is measured in __________.
- Energy stored in moving objects is called __________ energy.
- Energy stored due to height is __________ potential energy.
- Energy transferred by electric current is __________ transfer.
- Energy cannot be created or __________.
B. True or False
- Energy can disappear from a system.
- A stretched spring stores elastic potential energy.
- Hot objects have more thermal energy.
- Chemical energy is stored in food.
- Total energy always stays the same.
C. Short Answer
- What is an energy store?
- Name two energy transfer pathways.
- What energy change happens when an object falls?
- Why is some energy described as wasted?
✅ Show Answer Key
A. Fill in the Blanks
- joules
- kinetic
- gravitational
- electrical
- destroyed
B. True or False
- False
- True
- True
- True
- True
C. Short Answer
- A way in which energy is stored.
- Electrical and heating (any two).
- Gravitational potential energy changes to kinetic energy.
- It spreads to surroundings and becomes less useful.
© Aviate Learning – Changes in Energy Systems (Year 8)