Energy transfers

What is a system

An object or group of objects

When is energy transferred

when there is a change in a system

What is a system

An object or group of objects

When is energy transferred

when there is a change in a system

Nuclear store

Energy stored in the nucleus of an atom. Atomic nuclei release energy from their nuclear store during nuclear reactions

what is a kinetic store

Moving objects have energy in their kinetic store

what is a gravitational store

objects gain energy in their gravitational potential store when they are lifted through a gravitational field

what is an elastic store

Objects have energy in their elastic potential store if they are stretched, squashed or bent

what is a magnetic store

Magnetic materials interacting with each other have energy in their magnetic store

What is an electrostatic store

Objects with charge (like electrons and protons) interacting with one another have energy in their electrostatic store

What is a chemical store

Chemical reactions transfer energy into or away from a substance's chemical store

what is a thermal store

All objects have energy in their thermal store, the hotter the object, the more energy it has in this store

How is energy transferred

through energy transfer pathways

Mechanical working

When a force acts on an object (e.g. pulling, pushing, stretching, squashing)

Electrical working

A charge moving through a potential difference (e.g. current)

Heating (particles)

Energy is transferred from a hotter object to a colder one (e.g. conduction)

Heating (radiation)

Energy transferred by electromagnetic waves (e.g. visible light)

Mnemonic for energy transfer pathways

My Elephant Heavily Reads Harry Potter

Equation for efficiency

useful energy output / total energy input x 100

what is total energy input equal to

total energy output - this is because of the law of the conservation of energy

Equation for Total energy output

useful energy output + wasted energy

What is a sankey diagram

A visual representation of energy transfers

What does the left hand side of a Sankey diagram represent?

The left-hand side of the arrow (the flat end) represents the energy transferred into the system

What does the straight arrow represent in a sankey diagram?

The straight arrow pointing to the right represents the energy that ends up in the desired store; this is the useful energy output

What does the arrow that bends away represent in a sankey diagram

The arrows that bend away represent the wasted energy

Total energy in =

Useful energy out + Wasted energy

How is energy transferred

Conduction, Convection, Radiation

What makes a material a good conductor

if it transferes energy by heating

What are poor conductors called

Insulators - they prevent energy transfer

Why are metals good conductors

The delocalised electrons can collide with the atoms, helping to transfer the vibrations through the material and hence transfer heat better

What is convection

the main method of energy transfer in liquids and gases

Process of convection currents

The molecules push each other apart, making the fluid expand

This makes the hot fluid less dense than the surroundings

The hot fluid rises, and the cooler (surrounding) fluid moves in to take its place

Eventually, the hot fluid cools, contracts and sinks back down again

The resulting motion is called a convection current

Where is energy transfer unwanted

Keeping a house warm

Keeping a drink hot or cold

Dressing to stay warm in cold weather

what reduces conduction

insulators

what reduces convection

fluid and gas being prevented from moving