Science notes, unit 7
Energy
Textbook Science Year 4 (DLP), pages 123–140
What this chapter covers
- You can explain what energy means and name the sources of energy (7.1.1, 7.1.2)
- You can state the forms of energy and give examples of each (7.1.3)
- You can describe how energy changes from one form to another in daily life (7.1.4)
- You can explain that energy cannot be created or destroyed, but can be transformed (7.1.5, 7.1.6)
- You can classify energy sources as renewable or non-renewable and give reasons (7.2.1)
- You can explain why we must use energy wisely and how to do it (7.2.2, 7.2.3)
Everything that moves, glows, gets hot or makes a sound needs energy. In this unit you will find out where energy comes from, what forms it takes and how it changes from one form to another.
7.1Energy and its sources
Energy is the ability to do work. Energy can come from many sources.
| Source | How we get energy from it |
|---|---|
| Sun | The main source of energy. Solar panels use sunlight to generate electricity. |
| Water | Flowing water turns a turbine in a hydroelectric dam to generate electricity. |
| Wind | Blowing wind turns a windmill to generate electricity. |
| Waves | Ocean waves turn a turbine to generate electricity. |
| Biomass | Waste from firewood, plants and animal faeces is used as fuel and to generate electricity. |
| Fossil fuels | Petroleum, natural gas and coal are burned to generate electricity. |
| Nuclear substances | Uranium is used at nuclear power stations to generate electricity. |
| Geothermal | Heat from hot rocks under the Earth's surface turns a turbine. |
Did you know? Many of these sources work by turning a turbine. The turning turbine is used to generate electricity.
Name three energy sources that turn a turbine to generate electricity.
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Any three: water (hydroelectric dam), wind (windmill), waves, geothermal heat.
Forms of energy
Energy is found in nine forms.
| Form | What it is | Example |
|---|---|---|
| Solar energy | Energy obtained from the Sun | Sunlight on a solar panel |
| Heat energy | Energy stored in objects that are heated | A pot on a hot stove |
| Light energy | Energy produced by objects that give out light | A torch, a lit bulb |
| Sound energy | Energy produced by vibrating objects | A guitar string |
| Electrical energy | Energy flowing in a complete electrical circuit | Current in a lamp circuit |
| Chemical energy | Energy stored in food, fossil fuels, biomass and batteries | Rice, petrol, a dry cell |
| Kinetic energy | Energy of moving objects | A cyclist, a running child |
| Potential energy | Energy stored in objects that are high up, stretched or compressed | A catapult pulled back |
| Nuclear energy | Energy inside nuclear substances | Uranium |
Do not mix up the two stored forms. Chemical energy is stored in substances (food, petrol, batteries). Potential energy is stored because of position or shape (height, stretched, compressed).
Name the form of energy in (a) a rolling ball, (b) a stretched rubber band, (c) a plate of nasi lemak.
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(a) Kinetic energy (b) Potential energy (c) Chemical energy
Transformation of energy
Energy can change from one form to another. This is called transformation of energy. In a chain, an arrow → means "changes to" and + means "and".
| Situation | Energy chain |
|---|---|
| Riding a bicycle | Chemical energy (food) → kinetic energy |
| Switching on a television | Electrical energy → light energy + sound energy |
| Lighting a fire | Chemical energy (fuel) → heat energy + light energy |
| Diving from a diving board | Potential energy → kinetic energy → sound energy |
| Switching on a torch | Chemical energy (battery) → electrical energy → heat energy + light energy |
| Using a solar calculator | Solar energy → electrical energy → light energy |
| A moving car | Chemical energy (fossil fuel) → kinetic energy |
| Photosynthesis | Light energy (Sun) → chemical energy (starch) |
Did you know? A bulb gives out heat as well as light. That is why a lit bulb feels warm.
Example: a mobile phone
While you call, the phone's battery changes chemical energy to electrical energy. Then the electrical energy becomes light (screen) and sound energy (speaker).Write the energy chain for a radio that is plugged in and playing.
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Electrical energy → sound energy.
Energy cannot be created or destroyed
Energy cannot be created and cannot be destroyed. It can only be transformed from one form to another.
Think of a motorcycle. It does not make its own kinetic energy. The engine changes the chemical energy in petrol into kinetic energy. While it moves, some energy also changes to sound and heat. When the petrol is finished, the motorcycle stops. The kinetic energy has not been destroyed. All the chemical energy has been changed into other forms.
| Chemical energy (petrol) | → | Kinetic energy + heat energy + sound energy |
|---|
"The energy is used up" is not correct. Energy is never lost. It changes into other forms, often heat and sound that we do not use.
A girl rides a bicycle, then stops pedalling and the bicycle slowly stops. Has the kinetic energy been destroyed?
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No. Energy cannot be destroyed. The kinetic energy changed into other forms such as heat and sound.
7.2Renewable and non-renewable energy sources
| Renewable | Non-renewable | |
|---|---|---|
| Meaning | Can be generated continuously. It does not run out. | Limited and cannot be regenerated. It will run out. |
| Examples | Sun, waves, water, wind, biomass | Fossil fuels (coal, natural gas, petroleum) and nuclear substances (uranium) |
| Why | The Sun is constant; waves, water and wind are always there; biomass comes from natural substances. | Fossil fuels will run out in the future. Uranium is limited. |
Did you know? Biodiesel is made from vegetable oil or animal fat. Since February 2019, petrol stations in Malaysia sell diesel mixed with palm oil biodiesel.
Biomass is renewable but it is not the same as a fossil fuel. Fossil fuels take millions of years to form, so we cannot make more in our lifetime.
Is natural gas renewable or non-renewable? Give a reason.
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Non-renewable. It is a fossil fuel, it is limited and will run out.
Using energy wisely
Most energy we use today comes from non-renewable sources. To make sure there is enough energy in the future, we must use energy wisely.
| Why it is important | How we can do it |
|---|---|
| To prevent wastage of energy, so sources last longer and bills are lower | Switch off lights and fans when you leave a room. Use a fan instead of an air conditioner when possible. |
| To reduce pollution of the environment (burning fuels gives smoke) | Walk, cycle or share a car. Use public transport. Use renewable energy, such as solar energy. |
Example: the electricity bill
Ali's family leaves the air conditioner on all day. The bill is high. Next month they use a fan and switch off the lights when not needed. The bill falls because less electrical energy is used.Give one way to use energy wisely at school.
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Any: switch off lights, fans and computers when not in use; walk or cycle to school; share a ride.
Pictures: Science Year 4 (DLP) textbook, pp. 123–140 (forms of energy pp. 126–127, transformations pp. 128–130, renewable chart p. 134).
Summary
| Idea | Remember |
|---|---|
| Energy | The ability to do work |
| Forms | Solar, heat, light, sound, electrical, chemical, kinetic, potential, nuclear |
| Transformation | Energy changes form, e.g. chemical → kinetic when cycling |
| Law | Energy cannot be created or destroyed, only transformed |
| Renewable | Sun, waves, water, wind, biomass |
| Non-renewable | Coal, natural gas, petroleum, uranium |
| Use wisely | To prevent wastage and reduce pollution |