Energy Stores and Transfers

Where is energy stored?

In energy stores

Gravitational potential store

Energy stored in an object, when it’s lifted above ground. As the object falls, energy is transferred

Kinetic energy store

Energy stored in an object when it’s moving. When the motion changes, energy is transferred

Thermal energy store

Energy stored in objects due to their temperature. When an object is heated or cooled, energy is transferred

Chemical energy store

Energy stored in chemical bonds of substances e.g. a battery. Energy is transferred during chemical reactions

Elastic potential energy store

Energy stored when an object is squashed or stretched. When the object is released, energy is transferred

Electrostatic energy store

Energy stored in charged particles. When particles are attracted or repelled, energy is transferred

Magnetic energy store

Energy stored in magnetic materials. When magnets are attracted or repelled, energy is transferred

Nuclear energy store

Energy stored in atomic nuclei. When nuclei are split or fused, energy is transferred

How is energy transferred?

Between energy stores

What can energy transfers occur?

Between different stores in the same object, OR between the same stores in different objects, OR between different stores in different objects

Mechanical transfer pathway

Energy is transferred mechanically when a force acts over a distance

Electrical transfer pathway

Energy is transferred electrically when charged particles flow

Heating transfer pathway

Energy is transferred by heating when particles transfer energy from a hotter object to a colder one

Radiation transfer pathway

Energy is transferred by radiation when electromagnetic radiation transfers energy

What is an energy flow diagram?

A flow diagram showing the energy stores and transfers taking place within a system

What is a Sankey diagram?

A diagram representing energy transfers. They’re characterised by splitting arrows that show the proportions of the energy transfers taking place

What do the different parts of the arrow in a Sankey diagram represent?

The left-hand side of the arrow (the flat end) represents the energy transferred into the system, the straight arrow pointing to the right represents the energy that ends up in the desired store; this is the useful energy output and the arrow(s) that bend away represent the wasted energy

Total energy in =

Useful energy out + Wasted energy

What a system in physics?

An object or group of objects

What happens when a system is equilibrium?

Nothing changes and so nothing happens

What happens when there’s a change in a system?

Things happen, and when things happen energy is transferred

What is energy measured in?

Joules (J)

What is an open system?

Allows the exchange of energy and matter to or form from it’s surroundings

What is a closed system?

Can exchange energy but not matter to or from its surroundings

What is an isolated system?

Doesn’t allow the transfer of matter or energy to of from its surroundings

What is the principle of conservation of energy?

Energy cannot be created or destroyed, it can only be transferred from one store to another; meaning that the total amount of energy in a closed system remains constant

What must the total energy transferred into a system be equal to?

The total energy transferred out of the system - therefore energy is never ‘lost’ but it can be transferred to the surroundings by being dissipated (spread out) to the surroundings by heating and radiation; dissipated energy transfers are often not useful (wasted energy)