成人快手

Key points

  • can be described as being in different 鈥榮tores鈥.

  • Energy cannot be created or destroyed.

  • Energy can be transferred from one store to another.

Back to top

What is energy?

Energy is a quantity that is conserved - it cannot be created or destroyed. Energy can be stored and transferred.

One way we can understand energy is to use a .

Have a look at the table that uses money as a model to help us understand energy.

Idea it is explainingMoney as a modelHow the model links to energy
Energy鈥檚 ability to be storedWe store our money in pockets, purses and bank accounts.Energy is stored. For example, energy is stored in the kinetic energy store in objects that move.
Energy can be transferredWhen we pay for an item in a shop we are transferring our money from one store (pocket, purse or wallet) to another (the till).Energy can be transferred between different stores.
The unit of energyIn the United Kingdom, money is measured in pounds sterling (拢).Energy is measured in (J).
Back to top

Energy stores

There are several stores of .

A woman, dressed in athletic clothing, running along the beach

Kinetic energy store

The runner has more energy in their kinetic energy store when they are running faster.

The amount of energy in the kinetic energy store depends on the speed of the object.

A woman, dressed in athletic clothing, running along the beach
A woman reaching for a cardboard box from the top shelf of a cabinet.

Gravitational potential energy store

The box has more energy in its gravitational potential energy store when it is placed on a higher shelf.

The amount of energy in the gravitational potential energy store depends on the height of the object.

A woman reaching for a cardboard box from the top shelf of a cabinet.
A cup of tea with a matching saucer and glass of water, sitting on a wooden tray

Thermal energy

An object has more energy in its thermal energy store when it is hot than when it is cold.

The amount of energy in the thermal energy store depends on the temperature of the object.

A cup of tea with a matching saucer and glass of water, sitting on a wooden tray
A decorated cupcake with red casing and a lit single red candle on top

Chemical energy

Batteries, foods and fuels store energy in their chemical energy stores. The candle wax in the picture is a type of fuel.

Transfer of energy from the chemical energy store occurs due to chemical reactions.

A decorated cupcake with red casing and a lit single red candle on top
An athletic man crouched exercising with a resistance band in a kitchen.

Elastic potential energy

A stretched or squashed object has more energy in its elastic energy store.

The amount of energy in the elastic energy store depends on the amount of extension or compression.

An athletic man crouched exercising with a resistance band in a kitchen.
Back to top

Conservation of energy

A hand drawn black and white illustration of an enlightenment-era woman.
Image caption,
脡milie du Ch芒telet

In the 18th century the French philosopher, 脡milie du Ch芒telet, did an experiment. She dropped a number of balls from different heights then observed how they fell and their impact with the surface they landed on.

She found that the amount of the balls had when held high up was the same as the amount of energy they had when they were moving.

After analysing all of her data, du Ch芒telet concluded that energy cannot be created or destroyed.

This is now known as the Law of Conservation of Energy which means that energy doesn鈥檛 appear or disappear.

Energy can be transferred between different stores of energy.

When energy transfers take place in a :

the total energy stored before = total energy stored after.

For example:

A hand drawn black and white illustration of an enlightenment-era woman.
Image caption,
脡milie du Ch芒telet
The gravitational potential energy and kinetic energy of a ball as it falls to the ground. The gravitational potential energy decreases and the kinetic energy increases as the ball falls.
Figure caption,
When a ball falls to the ground, the gravitational potential energy decreases and the kinetic energy increases
Back to top

Video - conservation of energy

Back to top

Energy transfers

Energy can be transferred by:

  • mechanical working 鈥 when a force is applied to move an object through a distance

  • electrical working 鈥 when charge flows (electricity)

  • heating 鈥 when energy is transferred between hotter and colder regions

  • radiation 鈥 when energy is transferred as a wave, for example as light or sound

Back to top

Representing energy transfers

We can show how energy is transferred by using a transfer diagram.

A young girl standing on a stool and reaching for a book from a high bookshelf

Mechanical

A force is applied to move an object, for example when a person lifts a book onto a high shelf.

A young girl standing on a stool and reaching for a book from a high bookshelf
A flow chart showing energy in chemical store in muscles is transferred by doing mechanical work into energy in gravitational store of a book.
A toy model of a modern train on a track

Electrical work

Charges flow in a circuit, for example in a battery powered toy train.

A toy model of a modern train on a track
A flow chart showing energy in chemical store in a battery is transferred by doing electrical work into energy in kinetic store of a toy train.
A pair of open palms holding a packet of something

Heating

Energy moves from the thermal store of a hotter object to the thermal store of a cooler object, for example when a handwarmer is used to warm up your hands.

A pair of open palms holding a packet of something
A flow chart showing energy in thermal store in a handwarmer is transferred by conduction into energy in thermal store of hands.
A bird's eye view of two slices of brown bread inside a toaster.

Radiation

Energy is transferred as a wave, for example infra red radiation from a toaster to a slice of bread.

A bird's eye view of two slices of brown bread inside a toaster.
A flow chart showing energy in thermal store of a grill element is transferred by infrared radiation into energy in thermal store of food.
Back to top

Energy dissipation

When is transferred within a , energy can be . This is where energy is 鈥榳asted鈥 by being transferred out to the surroundings. Energy becomes stored in less useful ways.

Energy is usually dissipated to the surroundings by heating, though sometimes energy is dissipated by radiation, for example by sound waves.

The ways in which energy is dissipated depends on the system.

A stack of multi-coloured items, including towels and other clothing, inside a tumble dryer.

For example, in a tumble dryer:

  • The electrical work is done so energy is transferred usefully into the thermal energy store of the tumble dryer and the kinetic energy store of the tumble dryer. This helps to dry the clothes.

  • Energy is dissipated to the surroundings by sound waves and by heating. This is not useful.

A stack of multi-coloured items, including towels and other clothing, inside a tumble dryer.
Back to top

Test your knowledge

Quiz

Back to top

Teaching resources

Looking for more resources to inspire and engage your students? In this collection of Physics clips, Professor Brian Cox explains how our world today originated from a few fundamental scientific laws.

成人快手 Teach has thousands of free, curriculum-linked resources to help deliver lessons - all arranged by subject and age group.

Back to top

Play the Atomic Labs game! game

Try out practical experiments in this KS3 science game.

Play the Atomic Labs game!
Back to top

More on Energy

Find out more by working through a topic