# Energy and Temperature Changes

## Energy

Energy is measured in Joules (J). There are several different energy stores.

For example:

• Thermal energy
• Chemical energy
• Gravitational potential energy
• Elastic potential energy

Energy is linked to temperature. When a substance’s thermal energy store increases, its particles vibrate more. In the context of liquids or gases, you can describe vibrating particles as moving more rapidly.

As the thermal energy store of the substance increases, the temperature of the substance increases.

## Temperature

Temperature is a measure of how hot or cold something is. We can measure the temperature by using a thermometer, which you can see below.

Temperature is measured in degrees Celsius (°C)

### Thermal equilibrium

Energy always transfers from hotter objects to cooler ones.

This process will continue to occur until thermal equilibrium is reached, which is the point at which both of the objects are at the same temperature. Once this occurs, no more energy is transferred between the objects.

For example, if a cup of coffee is 30 °C and the temperature of the room is 10°C, heat will be transferred from the hotter coffee to the cooler surroundings.

This process continues until the coffee and the room reach the same temperature, indicating thermal equilibrium.

### Energy transfer by heating

Energy can transfer from a hot object to a cooler one through conduction, convection and radiation.

Conduction: Energy is transferred by direct contact

Convection: Warm particles rise and cooler particles sink, leading to a circulation of particles and the transfer of thermal energy.

Radiation: Energy is transferred by electromagnetic waves

## Energy vs Temperature

An object can have a higher temperature than another object but have less thermal energy.

For example, consider a lukewarm swimming pool and a kettle filled with boiling water. While the kettle may be hotter, the swimming pool has a larger thermal energy store due to its volume. This is because the swimming pool contains a greater number of particles.

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