What does energy do?

Energy is used to drive cars around, make sounds, clothes dry and also to charge your phone. It is hard to explain what energy is, because you can’t see it or weigh it. However, we can see what energy does.

Energy is needed to move or heat something, to make noise or light, or to change an objects shape. Energy makes things happen.

💡 Counting calories

You may have heard of a unit of energy called the calorie. This is used in some countries of the world to measure food energy.

One calorie is the amount of energy needed to raise the temperature of 1 gram of water by 1˚C. This is roughly 4.2 joules.

Measuring energy

• Energy is measured using a unit called the joule (Symbol J).
• You use one joule of energy when you lift 1kg bag of potatoes 10cm off the floor
• A batch of 1000 joules is known as a kilo joule.

Food energy is commonly measured in kilo joule (kJ). Even larger amounts of energy, such as electrical energy, are measured in Megajoule (MJ).

Forms of energy

• Kinetic energy– is the energy of movement. Anything that moves has kinetic energy,. The faster an object moves, the more kinetic energy it has.
• Heat Energy– can come from the Sun, flames, chemical reactions, electrical devices or even from a person or animal. Heat warms, burns, dries, melts, and makes hot-air balloons rise.
• Light energy– comes from the Sun, light globes, fires and animals such as glow-worms. Without light energy, the world would be a very dark place.
• Sound energy- is the energy that air has when it is vibrating. Your ears and brain interpret the vibrating of air as sounds. Sound comes from your voice, musical instruments, cars and power tools.
• Electrical energy– is produced by power stations, solar cells, batteries and lightning. Electrical energy powers your TV,

Stored energy

Many of the objects around you have stored energy or potential energy. Petrol in a car’s fuel tank and books on a shelf both have potential energy. They are not using energy at the moment but have stored energy. Stored energy gives objects the potential to make things happen: the books can fall off the shelf and the petrol can burn.

The foods that you eat originally obtained energy from the Sun. Plants capture light from the Sun and convert it into chemical energy in the form of simple sugars. This happens in a process called photosynthesis. Plants such as wheat make sugars and then convert them into starch for storage.

When you eat the plants, their seeds, nuts or grains (or eat animals that have eaten them), your body uses the chemical energy from the simple sugars and starch as your energy source.

Here are the 4 different types of potential energy:

• Gravitational potential energy– is energy stored in an object when it is above the ground. The greater the height, the more gravitational potential energy an object has.
• Chemical energy– is energy stored in substances. This energy is released by your body when you digest food, and by cars when fuel is burnt. Wood, paper, apples, petrol and batteries all contain chemical energy.
• Elastic potential energy – is energy stored in a stretched or squashed spring. stretched rubber bands also store elastic potential energy, which is released when they are let go.
• Nuclear energy– is the energy stored inside the tiny atoms that make up all matter. Nuclear energy is released in a nuclear power plant, when a nuclear bomb explodes, and inside the Sun.

Energy transfer

Energy can be passed from one object to another. This is known as energy transfer.

Heat transfer

Kinetic energy is not the only type of energy that can be transferred. When you stand in front of a heater, heat energy is transferred from the heater to you, warming you up. Heat energy can be transferred in three ways:

• Conduction
• Convection
• Radiation

Conduction

Conduction happens when two objects are in contact. Heat transfers from the hotter object into the cooler one, until they are both the same temperature. Conduction explains why you get burnt if you touch a hot tripod or stove top. Conduction also explains why a can of lemonade feels cold. The can feels cold because heat transfers away from your warm hand into the metal of the can and and the cold drink inside.

Convection

Convection is the process of how heat flows through liquids and gases. It is convection that causes heat to rise, making it hotter near the ceiling than down on the floor, and it is convection that spreads heat from ducked heating vents through rooms of a house.

Radiation

Heat radiates (spreads outwards) from any hot object. This type of heat transfer is called radiation. Radiant heat is transferred as a wave that can travel even through the vacuum of space. This explains why you feel the heat of the Sun when you are outside. However, radiation is easily blocked. If you stand in a the shadow of a tree it feels much cooler, because the radiant heat of the Sun cannot get to you.

Energy transformation

Energy can be transferred from one object to another. Energy can also be changed, or transferred, from one type of energy into another type of energy.

Occasionally a number of different energy changes happen all at once. Imagine that you accidentally knock a glass of a table. The glass falls and smashes on the floor below. The glass initially has gravitational potential energy. When it is falling, this energy is changed into kinetic energy and some heat energy is changed into kinetic energy and some heat energy. When it hits the floor, some of the kinetic energy is transferred to the pieces of glass that break and fly off in all directions. Some kinetic energy is converted into heat energy and the sound of glass smashing.

The law of conservation of energy

The law of conservation of energy state that energy can never be created or destroyed. It can only be converted from on form to another.

This means that:

• Energy might be passed on or wasted but it is never lost
• If one object wastes energy, then it always gained by another object, usually as heat