Energy transfers
Systems and stores
The capacity for doing work. can remain in the same store for millions of years or sometimes just for a fraction of a second. There are energy transfers going on all the time - whenever a An object or group of objects. changes there is a change in the way some or all of the energy is stored.
Examples of energy transfers include:
Image caption, A swinging pirate ship ride at a theme park
Kinetic energy is transferred into gravitational potential energy
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Transferring energy
In each of these examples, energy is When something is moved from one place to another. This may be people, objects or energy. by one of the following four types of energy transfer:
- mechanical work - a force moving an object through a distance
- electrical work - charges moving due to a The potential difference (or voltage) of a supply is a measure of the energy given to the charge carriers in a circuit. Units = volts (V). This is the voltage between two points that makes an electric current flow between them.
- heating - due to temperature difference caused electrically or by chemical reaction
- radiation - energy transferred as a wave, eg light and infrared - light radiation and infrared radiation are Energy is 'given-out' by the material and the internal energy of the material will decrease. For example, infrared radiation from the Sun is emitted into space. from the sun
Doing 'work' is the scientific way of saying that energy has been transferred. For example, a grazing cow, a firing catapult and a boiling kettle are all doing 'work', as energy is being transferred.
Energy flow diagrams
Diagrams can be used to show how energy is transferred from one store to another. Two examples are the transfer diagram and the Sankey diagram.
Transfer diagrams
In transfer diagrams the boxes show the The different ways in which energy can be stored, including chemical, kinetic, gravitational potential, elastic potential and thermal stores. and the arrows show the The different ways in which energy can be transferred from one store to another includes heating, by waves, electric current or by a force moving an object..
For example, a transfer diagram for a child at the top of a slide may be:
Gravitational energy stored in the child at the top of the slide is transferred as mechanical work done to speed up and to do work against friction. The result of this is a shift of energy from The energy stored by an object lifted up against the force of gravity. Also known as GPE. to kinetic energy and internal energy (raising the temperature of the child and the slide).
Sankey diagrams
Sankey diagrams start off as one arrow that splits into two or more points. This shows how all of the energy in a system is transferred into different stores.
Sankey diagrams are really useful when the amount of energy in each of the energy sources is known. The width of the arrow is drawn to scale to show the amount of energy.