Everything about energy
In this topic you will:
- find out what energy is
- learn about different energy stores and transfers
- discover how some ways that energy can be stored more easily than others.
- learn about energy changing
- discover that energy changes when something happens
- learn how to give examples of changes in energy
- discover that when energy is changed, some of it may be wasted
- learn that some of this energy can never be recovered
Key Words
- chemical
- elastic potential
- electrical
- energy
- fuel
- gravitational potential
- joule
- kinetic
- light
- luminous
- sound
- stored
- thermal
- transferred
- process
- event
- dissipated
- recovered
- useful
- wasted energy
What is energy?
Energy is something that must be changed or transferred in order to do something.
There are many different ways that energy can be stored or transferred.
For example, kinetic energy is the energy in movement.
The unit for measuring the amount of energy is called the joule (J).
You need about:
- to walk up the stairs between two floors in a building.
- for every metre you run
- to bring 1 litre of cold water to boiling point.
Energy stores and transfers
There are many different ways in which energy is being stored or transferred around you all the time.
The table describes some of these stores and transfers.
| energy | description | energy store or energy transfer |
|---|---|---|
| kinetic | energy stored due to movement of an object | store |
| chemical | energy stored in food, batteries, chemical fuels such as wood, oil and coal | store |
| energy | description | energy store or energy transfer |
|---|---|---|
| thermal | heat energy stored in hot objects and transferred to colder objects | store or transfer |
| elastic potential | energy stored when things are stretched or squeezed to change their shape | store |
| gravitational potential | energy stored when an object is lifted away from a source of gravity | store |
| electrical | the flow of current in a circuit transfers electrical energy | transfer |
| sound | energy transferred from vibrating objects | transfer |
| light | visible energy from luminous objects (objects that give out their own light) that you can see | transfer |
Look at the descriptions of energy in the picture.
Questions
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You can learn them by using visual aids like diagrams, creating mnemonics, or using flashcards to remember the different types and definitions.
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Yes, creating a sentence using the first letter of each energy type (e.g., "The Energetic Kangaroo Chased Giant Elephants Singing Loudly") can help reinforce memory.
Storing energy
Energy can be stored more easily in some ways than in others.
For example, you can keep uncooked rice for a long time. That is a store of chemical energy.
Coal and crude oil are stores of chemical energy that formed millions of years ago. This shows that some energy stores can last for a very long time. A battery is another example of how chemical energy can be stored. It is quite easy to store chemical energy.
Gravitational potential energy is also easy to store. The picture shows a tank containing water. A pump has been used to lift up the water. The water stores gravitational potential energy.
Some energy stores only last for a short time.
Thermal energy (heat) is one example. Hot objects will eventually cool down (they will lose their store of thermal energy).
Kinetic energy is another example. Kinetic energy is more difficult than chemical or gravitational potential energy to store.
The tennis ball in the picture has a store of kinetic energy while the ball is moving, but the ball will eventually stop moving.
Rice is a store of chemical energy.
Questions
Copy and complete these sentences. Choose from the stores and transfers of energy you have learnt about.
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Chemical energy is stored in the battery.
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Electrical energy is transferred in the wires.
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Chemical energy
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Chemical energy
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Gravitational potential energy
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Gravitational potential energy
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Chemical energy (e.g. in fossil fuels), gravitational potential energy (e.g. in water stored in reservoirs)
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Kinetic energy — the object eventually stops moving
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Hot tea left in a cup will cool down over time, losing thermal energy to the surroundings.
Use some examples of different energy stores and transfers in your answer.
Discuss your answer with a partner.
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As population and development increase, more energy is used for transport, heating, industry, and electricity. This increases demand for chemical energy (fossil fuels), electrical energy (from power stations), and kinetic energy (in vehicles). Managing energy use becomes more important.
Connecting Concepts: Energy Stores, Transfers and What Comes Next
You’ve learned how energy can be stored in different ways — such as in food, fuels, batteries, and lifted objects — and how it can be transferred through movement, heat, sound, and electricity.
These ideas help us describe where energy is and how it moves. But there’s another important way to describe energy: by the form it takes while it's being stored or transferred.
In the next topic, you’ll explore the different forms of energy — including thermal, sound, light, electrical, and more — and learn how these forms help us understand what energy is doing in everyday situations.
Quick Fact
An energy store tells you where energy is held. A form of energy tells you what kind of energy it is — like heat, light, or movement.
How does energy change?
In Section 3.5, you learned that energy is something that must be changed or transferred in order to do something. Before energy can be changed or transferred, it is stored. When energy is stored, the energy is not doing anything.
The picture shows a cooking pot being heated on a fire.
The fuel for the fire is wood. Wood is a store of chemical energy.
Burning the wood changes the chemical energy to thermal energy (heat).
The thermal energy is then transferred to the pot and the food inside.
The people in the picture are walking up stairs.
They are changing chemical energy from their food into kinetic energy for movement.
The movement is taking the people higher, so kinetic energy is being changed to gravitational potential energy.
This picture shows a power station.
This power station is using the chemical energy stored in natural gas.
The gas is burned, which changes chemical energy to thermal energy.
The thermal energy is then changed to kinetic energy in large generators that spin around.
The kinetic energy is then changed to electrical energy.
The electrical energy is then transferred through wires into homes and buildings.
Energy changes are not always helpful. Typhoons, hurricanes, earthquakes and tsunamis are some examples of how energy changes can be very dangerous.
In all these examples, there is a process or event that changes or transfers the energy. For example, burning is a process.
Burning changes chemical energy stored in a fuel to thermal energy.
You can represent the processes as arrows and draw diagrams to show changes in energy.
Here are some other examples.
chemical → thermal
(A fire that burns wood changes chemical energy to thermal energy)
electrical → sound
electrical → light
(A television converts electrical energy to sound and light)
When a book falls from a shelf, that is an event. When the book is on the shelf, the book has stored gravitational potential energy. This energy is changed to kinetic energy as the book falls.
gravitational potential → kinetic
Questions
When something happens, energy is ________ or ________.
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dissipated, transferred
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chemical to light
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electrical to light
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chemical to kinetic
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electrical to sound
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chemical → kinetic
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chemical → thermal
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kinetic → gravitational potential
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gravitational potential → kinetic
What Happens to Energy After a Change?
You’ve learned that energy can be stored, transferred, and changed — for example, from chemical to kinetic, or electrical to light. These changes help objects move, heat up, light up, and make sounds.
But energy doesn’t disappear after a change happens. So what does happen to it? Where does it go? Why can’t we always use it again?
In the next topic, you’ll explore what happens to energy after it has been used. You’ll learn about energy being dissipated, how it spreads out, and why it becomes less useful — even though it’s never actually lost.
Quick Fact
Energy cannot be created or destroyed — but it can become spread out and harder to use. Scientists call this energy dissipation.
Useful and wasted energy
Every time you use energy to make something happen, energy is transferred or changed. Some of the energy transferred or changed is useful, but some of it is wasted.
Look at the picture of fuel being added to a motorcycle.
The motorcycle engine uses the chemical energy stored in the fuel.
This chemical energy is changed to useful kinetic energy to move the motorcycle and rider.
But chemical energy from the fuel is also changed into thermal energy and sound energy.
In fact, only about ¼ or 25% of the chemical energy in the fuel is used for movement.
The other ¾ or 75% of the energy is wasted energy. This wasted energy is dissipated and cannot be recovered.
Dissipated energy is energy that spreads out where there is no use for it.
You cannot gather thermal energy or sound and bring them back into one place to be stored, changed or transferred.
Look at the two types of lamp in the picture.
These two lamps emit the same brightness of light but they waste very different quantities of energy.
Both lamps A and B in the picture change electrical energy to light energy.
Lamp A only changes about 15% of the electrical energy into light. 85% of the electrical energy is wasted as thermal energy from this lamp. This is dissipated as thermal energy.
Lamp B changes about 50% of the electrical energy into light. 50% of the electrical energy is dissipated as thermal energy from this lamp.
Every time energy is changed or transferred, there is some thermal energy is wasted. This wasted thermal energy is dissipated.
Even when you want to produce thermal energy, some of it is wasted.
Look at the water being heated in this picture.
In the picture, chemical energy from wood is being changed to thermal energy by the process of burning.
Thermal energy is being used to heat the water.
Thermal energy is also being used to heat the rocks, the metal container and the air around it.
Some of the thermal energy is escaping in the steam.
The fire is also changing energy into light.
All these represent wasted energy that is dissipated and cannot be recovered.
For everything that uses energy change or transfer, some of that energy will always be dissipated.
Questions
- energy that spreads out and becomes less useful
- energy that becomes more useful
- energy that can be used later
- energy that is not useful but can be stored
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✔ energy that spreads out and becomes less useful
Choose all that are correct.
- chemical
- thermal
- light
- sound
- elastic
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✔ thermal, ✔ light, ✔ sound
List the energy as either useful or wasted.
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light (useful), thermal (not useful)
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chemical to kinetic (useful), thermal (not useful)
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kinetic (useful), sound (not useful)
Which of these graphs shows how the temperature changes with increasing distance from a hot object?
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Graph 3 — a curved line decreasing as distance increases
Think Like a Scientist
You will now do an experiment to investigate a change in energy. This is now an individual activity.
• Candle
• Safety glasses
• Glass beaker or metal can
• Tripod and gauze
• Thermometer
• Timer
• Heat-proof mat
• Stirring rod
• Cooking oil
• Matches
Step 2. Light the candle and place it under the beaker. Start the timer.
Step 3. Stir the oil regularly using the stirring rod. Do not use the thermometer to stir!
Step 4. Measure the oil temperature every minute. Record both time and temperature.
Step 5. Stop heating once the oil temperature has increased by 10°C.
Step 6. Carefully blow out the candle.
Step 8. Plot a line graph using your data. Put temperature on the vertical axis.
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Thermometers are fragile and could break if used for stirring. They are not designed for physical force.
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The energy came from the chemical energy stored in the candle, which was converted to thermal energy when burned.
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The candle burned and gradually melted, producing a flame that transferred heat to the oil.
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The metal beaker and the air around the flame were also heated.
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Use a lid to reduce heat loss and place the beaker closer to the flame to focus the heat.
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A line graph shows continuous change over time, making it easier to observe temperature trends.
Discuss each of these statements with a partner or in writing:
- We worked safely at all times.
- We recorded all the results at the right times.
- We took readings from the thermometer as accurately as possible.
- We put the correct column headings with units in the table.
- We drew the graph correctly and it shows the trend in the results.