Energy stores and transfers
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Explainer Video
Summary
Energy stores and transfers
In a nutshell
Energy cannot be created or destroyed, it can only be transferred from one store to another. There are many different energy stores and four ways in which it can be transferred. You can use transfer or sankey diagrams to represent energy transfers.
Definitions
Keyword | Definition |
| Work done | Work done is the energy transferred to or from an object using force |
| System | A system is an object or several objects |
Energy stores
Energy is the ability to do work and it can be stored and transferred. Energy can be stored in many ways, and the following are the stores you need to learn.
Energy Store | Description | Example |
| Electrostatic | Energy stored when positive and negative charges attract or repel. | Thunderstorms, nylon clothes, two balloons rubbed together |
| Nuclear | Energy stored in the nucleus of an atom. | Fusion in stars, fission reactions in nuclear power plants |
| Kinetic | Moving objects have kinetic energy. | Car, someone running, rolling a ball |
| Thermal | Objects with a temperature above () have thermal (heat) energy. | Everything! Unless something has a temperature of |
| Gravitational potential | When an object is in a gravitational field it has this energy store. The amount of energy stored depends on height, mass and strength of gravitational field. | Skydiver, ball thrown in the air, car at the top of a ramp |
| Elastic potential | Energy stored when objects are squashed or stretched. | Elastic band, spring, slinky |
| Chemical | Energy stored between chemical bonds. | Food, batteries, fire logs |
| Magnetic | Energy stored when poles attract or repel. | Fridge magnets, compasses |
Energy transfers
Energy can be transferred between the above stores in four different ways.
Energy Transfer | Description | Example |
| Mechanically | Energy transfers when a force is applied to an object | Pushing an object |
| Electrically | Energy transfers when charge flows | Electricity in a wire |
| By heating | Energy transfers from a hot region to a cold region | Water being boiled on a stove |
| By radiation | Energy is transferred as a wave | Sunlight |
Conservation of energy
Energy cannot be created or destroyed, it can only be transferred from one store to another.
However, energy stores are not perfect, and some energy gets lost, for example, by heating. Therefore, the total energy put into a system is equal to useful energy and wasted energy combined.
Example
Describe the energy stores and transfers for a toy car going down a ramp.
At the top of a ramp a toy car will have gravitational potential energy. This will be mechanically transferred to kinetic energy as the toy car goes down the ramp. Some energy will transfer into the surroundings in the form of sound or heat.
Energy transfer diagrams
Energy transfers between stores can be represented in two different ways.
Transfer diagrams
Transfer diagrams can be used to represent energy transfers when energy values are unknown. This type of diagram uses rectangles to represent stores, and an arrow to show which energy transfer took place.
Example
Draw an energy transfer diagram describing the chemical energy store transfer from your muscles to the kinetic energy in a bike when you are pushing it.
Sankey diagrams
Sankey diagrams are used when energy values are known. They are drawn using arrows to represent how much energy has been transferred as waste energy and useful energy.
Example
Draw and label a sankey diagram for a lightbulb that requires of energy. has been transferred to light energy, and has been transferred to heat energy.
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FAQs - Frequently Asked Questions
What are sankey diagrams?
Sankey diagrams are used when energy values are known to represent energy transfers. They are drawn using arrows to represent how much energy has been transferred.
What do energy transfer diagrams show?
Energy transfer between stores can be represented in a diagram. Rectangles are used to represent the different stores and labelled arrows are used to explain the type of energy transfer taking place.
What is the definition of the conservation of energy?
Energy conservation means energy cannot be created nor destroyed, it can only be transferred from one store to another.
What are the types of energy transfer?
Energy can be transferred between stores in the following four ways – electrically, mechanically, by heating and by radiation.