# 1.1.1 Energy Stores & Transfers

### Systems in Physics

• Energy is a property that must be transferred to an object in order to perform work on or heat up that object
• It is measured in units of Joules (J)
• This is regardless of what type of energy is stored ie. kinetic or chemical
• Energy will often be described as part of an energy system
• In physics, a system is defined as:

An object or group of objects

• Therefore, when describing the changes within a system, only the objects or group of objects and the surroundings need to be considered
• A thermodynamic system, for example, can be isolated, closed or open
• An open system allows the exchange of energy and matter to or from its surroundings
• A closed system can exchange energy but not matter to or from its surroundings
• An isolated system does not allow the transfer of matter or energy to or from its surroundings

A system can be open, closed or isolated

### Energy Stores & Transfers

#### Energy Stores

• Energy can be stored in different ways, and there are changes in the way it is stored when a system changes
• The principle of conservation of energy states that:

Energy cannot be created or destroyed, it can only be transferred from one store to another

• This means that for a closed system, the total amount of energy is constant
• There are many different ways that energy can be stored, these are shown in the table below:

Types of Energy Stores Table

#### Energy Transfers

• A system can change between stores through different energy transfer mechanisms
• Examples of these are:
• Mechanical
• Electrical
• Heating
• These are described in the table below:

Types of Energy Transfers Table

• An example of a thermal energy transfer is a hot coffee heating up cold hands

Thermal energy is transferred from the hot coffee to the mug and to the cold hands

### Author: Ashika

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.
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