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 diagrams to represent energy transfers.
Definitions
Key work
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 0K (−273°C) have thermal (heat) energy
Everything! Unless something has a temperature of −273°C
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
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.
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 conservation of energy?
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.
What types of energy stores are there?
There are 8 types of energy stores. These are chemical, elastic potential, electrostatic, gravitational potential, kinetic, magnetic, nuclear and thermal.
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