AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER
Energy stores and systems
Energy · Lesson 1 of 7
Warm-up
Answer each one, then check.
1. What is the unit of energy?
The joule (J)
2. What is a system?
An object or group of objects
3. Name the energy store in a stretched spring.
Elastic potential
4. Name the energy store in food and fuels.
Chemical
5. Can energy be created or destroyed?
No, it can only be transferred, stored or dissipated
Learning Objectives
1. Define a system and describe changes in the way energy is stored when a system changes.
2. Name the main energy stores and the four transfer pathways.
3. Describe the energy changes in common situations, such as an object projected upwards or a kettle boiling water.
4. Write clear statements using the phrase 'energy is transferred from ... to ...'.
Conservation Of Energy
Energy cannot be created or destroyed. It can be transferred usefully, stored or dissipated.
A system is an object or group of objects. When a system changes, there are changes in the way energy is stored.
Energy Changes in Two Systems
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Ask 'which store goes down and which goes up?' for every change. |
A ball thrown up changing kinetic energy into gravitational potential energy, and a kettle transferring electrical energy to the thermal store of water.
The Energy Stores
Learn the main stores and an example of each.
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Energy store |
Examples |
|---|---|
|
Kinetic |
Any moving object |
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Gravitational potential |
An object above the ground |
|
Elastic potential |
A stretched or compressed spring, an elastic band |
|
Thermal |
A hot object; the particles have more energy |
|
Chemical |
Fuels, food, batteries |
|
Nuclear |
The nucleus of an atom |
|
Magnetic |
Magnets and electromagnets |
|
Electrostatic |
Charged objects, such as a charged balloon |
Ways Energy Is Transferred
|
Mechanically A force moves an object through a distance (work done). |
Electrically Charge flows in a circuit (work done by the current). |
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By heating Energy flows from a hotter object to a cooler one. |
By radiation Energy is carried by waves, such as light and sound. |
A Ball Thrown Upwards
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Describe the changes in the way energy is stored when a ball is thrown upwards, until it reaches its highest point. |
1. Just after leaving the hand
The ball has a large kinetic energy store
2. As it rises
It slows down, so the kinetic energy store decreases
3. At the same time
Its height increases, so the gravitational potential energy store increases
4. Small effect
Some energy is transferred to the thermal store of the air by friction
Answer: Energy is transferred mechanically from the kinetic store to the gravitational potential store, with a little dissipated to the thermal store of the air.
Boiling Water in a Kettle
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Describe the changes in the way energy is stored when a kettle boils water. |
1. Electrical work
Charge flowing through the heating element transfers energy from the mains
2. Heating element
The thermal energy store of the element increases
3. By heating
Energy is transferred to the thermal energy store of the water, which increases
4. Wasted
Some energy heats the kettle and the surroundings
Answer: Energy is transferred electrically and then by heating to the thermal store of the water; some is dissipated to the surroundings.
Writing Good Answers
Use the language of stores and transfers.
▸ Name the stores. Say 'the kinetic energy store decreases', not 'kinetic energy is lost'.
▸ Say how. Give the pathway: mechanically, electrically, by heating or by radiation.
▸ Say where the rest goes. Mention dissipation to the surroundings if the system is not perfectly efficient.
▸ Total energy. The total energy after the change is the same as before.
Key Terms
|
System An object or group of objects. |
Energy store A way energy is held, such as kinetic or thermal. |
|
Transfer Energy moving from one store to another. |
Dissipated Spread out to the surroundings in less useful stores. |
|
Closed system A system where no energy enters or leaves. |
Work done Energy transferred by a force or a current. |
Your Task: Store to Store
10 minutes
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For each situation, name the store that decreases and the store that increases. (a) A car braking. (b) A book falling off a shelf. (c) A battery powering a motor lifting a weight. (d) A bow being drawn and released. 1. Name the store before. 2. Name the store after. |
A good answer shows: (a) Kinetic decreases; thermal (brakes) increases. (b) Gravitational potential decreases; kinetic increases. (c) Chemical decreases; gravitational potential increases (plus some thermal). (d) Chemical (archer) to elastic potential, then elastic decreases; kinetic of the arrow increases.
Can I...?
☐ Name the main energy stores.
☐ Name the four transfer pathways.
☐ Define a system.
☐ Describe energy changes for an object projected upwards.
☐ Describe energy changes when a vehicle slows down.
☐ Describe how a kettle heats water.
☐ Use 'increases' and 'decreases' correctly.
☐ State that total energy is conserved.
Summary
✓ Energy can be transferred, stored or dissipated but not created or destroyed.
✓ Describe changes with 'store decreases' and 'store increases'.
✓ Pathways: mechanically, electrically, by heating, by radiation.
✓ In a closed system the total energy does not change.
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EXAM FOCUS A car slows down to a stop using its brakes. Describe the changes in the way energy is stored. (2 marks) Say which store decreases and which increases. |