Energy Stores & Transfers
Energy Storesvideo
Energy Stores
Energy is a property that must be transferred to an object to perform work on or heat up that object
Energy is measured in units of joules (J)
Energy will often be described as part of an energy system
In physics, a system is defined as:
An object or group of objects
Defining the system, in physics, is a way of narrowing the parameters to focus only on what is relevant to the situation being observed
A system could be as large as the whole Universe, or as small as an apple sitting on a table
When a system is in equilibrium, nothing changes, and so nothing happens
When there is a change to a system, energy is transferred
If an apple sits on a table, and that table is suddenly removed, the apple will fall
As the apple falls, energy is transferred
Example of Energy Transfer
Energy is transferred when the apple is falling - the system is changing
Energy is stored in objects in different energy stores
Descriptions of Energy Stores
Energy Store | Description |
|---|---|
Kinetic | Moving objects have energy in their kinetic store |
Gravitational | Objects gain energy in their gravitational potential store when they are lifted through a gravitational field |
Elastic | Objects have energy in their elastic potential store if they are stretched, squashed or bent |
Magnetic | Magnetic materials interacting with each other have energy in their magnetic store |
Electrostatic | Objects with charge (like electrons and protons) interacting with one another have energy in their electrostatic store |
Chemical | Chemical reactions transfer energy into or away from a substance's chemical store |
Nuclear | Atomic nuclei release energy from their nuclear store during nuclear reactions |
Thermal | All objects have energy in their thermal store, the hotter the object, the more energy it has in this store |
Energy Transfersvideo
Energy Transfers
Energy is transferred between stores through different energy transfer pathways
The energy transfer pathways are:
Mechanical
Electrical
Heating
Radiation
These are described in the table below:
Energy Transfer Pathways Table
Transfer Pathway | Description |
|---|---|
Mechanical working | When a force acts on an object (e.g. pulling, pushing, stretching, squashing) |
Electrical working | A charge moving through a potential difference (e.g. current) |
Heating (by particles) | Energy is transferred from a hotter object to a colder one (e.g. conduction) |
(Heating by) radiation | Energy transferred by electromagnetic waves (e.g. visible light) |
An example of an energy transfer by heating is a hot coffee heating up cold hands
Energy Transfers Scenario
Energy is transferred by heating from the hot coffee to the mug, to the cold hands