Energy transfers in a system

System

An object or group of objects

Closed system

A system in which there is no net change to the total energy

Law of conservation of energy

Energy can be transferred usefully, stored or dissipated, but cannot be created or destroyed

Useful energy transfer

When energy is transferred by a device to energy stores we want

Wasted energy transfer

When energy is transferred by a device to energy stores we don't want

Dissipate

When energy spreads out and is transferred to energy stores into less useful forms

Dissipated energy

Energy which is wasted and is usually transferred to the surroundings, causing them to heat up

Lubricate

When a substance is used to reduce wasted energy transfers by reducing the friction between moving parts

Insulate

When a substance is used to reduce wasted energy transfers by reducing the amount of heat that is transferred to the surroundings

Thermal conductor

A material that allows charge or heat to pass through it easily

Thermal insulator

A material that does not allow charge or heat to pass through it easily

Thermal conductivity

The rate of energy transfer by conduction through a material

Conduction

When heat is transferred through a material due to vibrating particles colliding and transferring energy from one particle to another

Convection

When heat is transferred through a moving liquid or gas due to differences in densities

Radiation

When heat is transferred from a hot object due to the object emitting infrared (heat) radiation