What is energy?

Energy is in everything around us. Without energy nothing would ever change, move, make a sound or even be visible.

In this article you can learn about:

• Where energy comes from
• What conservation of energy is
• What useful and wasted energy are
• What the main types of energy are

This resource is suitable for energy and sustainability topics for primary school learners.

Find out where energy comes from and what the main types of energy are in this short video.

All the different forms of energy can be traced back to the Big Bang.

Scientists believe that everything in the Universe was once packed into a tiny point. 13.8 billion years ago, the Big Bang was when this tiny point flew apart in a massive explosion, spreading matter and energy out in all directions and creating the Universe.

Matter is ‘stuff’, anything that has mass and takes up space. For example:

• you
• a ball
• the air around you
• the Earth, Moon and Sun.

Energy is the ability of matter to change or do something. For example

• we use energy to breathe or throw a ball
• the ball has energy as it moves through the air
• energy from the Sun gives out light that lets us see the ball

All of this energy can be traced back to the Big Bang.

There is a scientific rule called the law of conservation of energy. It explains that:

Energy cannot be created or destroyed, only transferred between different forms and different objects.

For example:

• Light energy from the Sun is transferred into electrical energy (another form of energy) by a solar panel.
• Heat energy from a hot water bottle is transfers to a bed (another object).

The Sun is the Earth’s main source of energy. Find out more about the power of the Sun here: What is the Sun?

In daily life, we can talk about energy transfers in terms of useful energy, which is used for something, and wasted energy, which is lost in some way.

For example, a hairdryer transfers electrical energy into two forms of useful energy:

• Heat energy that warms the air.
• Kinetic energy that moves this hot air.

These are useful energy because they are the things that dry your hair.

The hairdryer transfers some electrical energy into wasted energy:

• Heat energy that is lost to your surroundings.
• Sound energy that makes the hairdryer noisy.

These are wasted energy because they don’t help dry your hair.

Potential energy is energy stored because of its position or state. For example:

• An elastic band that has been stretched tight has the potential to snap back to its relaxed position.

• A skateboarder at the top of a ramp has the potential to roll down the ramp because of gravity.

Chemical energy is a type of stored energy. It is stored in the bonds that hold atoms and molecules together. It is released and can be used when these bonds break. For example

• Chemical energy stored in food is released when we digest it and can be used by our bodies
• Chemical energy stored in fuels like gas can be used to heat our homes or cook food.
• Chemical energy stored in batteries can be used to generate electricity for mobile phones or remote controls.

Learn more about food and the chemical energy it gives us when we digest it:

• Find out how food gives our body fuel: Food as fuel
• Find out what our human body does with the food that we eat: How do humans digest food?

Kinetic energy is the energy of movement. An object has kinetic energy when it is moving. For example:

• When a football player kicks the ball, the ball has kinetic energy while it moves through the air.
• A goalie has kinetic energy while she dives to catch the ball.

Heat energy is the flow of energy from something warmer to something cooler. For example:

• Heat energy radiated by the Sun warms the Earth and all the living things and objects on it.
• Heat energy from a cup of tea is conducted through the cup and warms your hands.
• Heat energy from a radiator warms the air around it which rises up and moves around, heating the room. This is called convection.

Electrical energy comes from the movement of electrical charge. Electrical energy is useful because it can be transferred into lots of different types of energy. For example:

• Electrical energy can be transferred to heat energy to boil a kettle.
• Electrical energy can be transferred to light energy in a lightbulb.
• Electrical energy can be transferred to kinetic energy to move an electric car.

We can also use lots of different forms of energy to generate electrical energy. For example:

• Solar panels transfer light energy to electrical energy.
• Wind turbines transfer kinetic energy to electrical energy.
• Batteries transfer chemical energy to electrical energy.

We need light energy to see. Light energy is reflected off objects and into our eyes. When this energy hits the back of our eyes, signals are sent to the brain, which then works out the size, shape, position and colour of whatever the light has reflected off.

Our main source of light is the Sun. During the day, light energy from the Sun lights up the side of the planet facing it. At night, we often see the Sun's light energy reflected off the surface of the moon. We can also see light energy from stars that are billions or trillions of miles away.

We have lots of ways to make light ourselves:

• Candles change chemical energy to light energy by burning wax as a fuel.
• Lightbulbs change electrical energy to light energy.
• TVs, phones and tablets change electrical energy to light energy that lights up a screen.
• Glowsticks change chemical energy to light energy by mixing different chemicals together.

Sound energy is energy which can be heard by living things. It is the movement of energy through a substance such as water or air and is transmitted in waves. Sound energy is caused by vibrations in solids, liquids or gases. Humans and animals have used this to communicate, but many types of energy also produce sound energy. For example:

• The heat energy of a burning fire produces sound energy that we hear as crackling sounds.
• The kinetic energy of a guitar string vibrating produces sound energy.
• The electrical energy of lightning makes the air around it expand producing sound energy that we hear as thunder.

Big Bang - The name given to an explosion which happened 13.8 billion years ago which created all matter in our universe.

Matter - Anything that has mass and takes up space.

Energy - The ability of matter to change or do something.

Law of conservation of energy - A scientific law that explains that energy can be transferred but not created or destroyed.

Examples of energy transferring

Here are some examples of energy transferring between different objects and forms of energy that we have learned about:

• The Sun’s heat and light energy is transferred into chemical energy by an apple tree to grow apples.

• A person eats the apple and the chemical energy of the food is transferred to the person's body.

• The chemical energy stored in the person's body is transferred to kinetic energy when the person moves around…

Find some other examples of energy transferring between different forms and objects like the examples above.