Energy and Temperature

Energy

Energy is measured in joules (J), and it can exist in various forms, known as energy stores.

For example:

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

Energy is linked to temperature; when the thermal energy store of an object increases, its particles vibrate more rapidly. When talking about liquids or gases, you can describe vibrating particles as moving more.

As the thermal energy store of the object increases, the object’s temperature 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.

A vertical thermometer displaying a temperature scale in degrees Celsius. The scale ranges from -20°C to 50°C, with clear markings at each 10-degree interval. The red mercury column inside the thermometer reaches approximately 20°C, indicating the current temperature.

  • Temperature is measured in degrees Celsius (°C)

Thermal equilibrium

Energy naturally transfers in this direction: from hot objects to cold objects.

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

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

A steaming cup of coffee on a saucer. The cup's surface is labelled with a temperature of 30°C. Four red arrows pointing towards the cup from all sides indicate that the surrounding temperature is 10°C each.

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

A steaming cup of coffee on a saucer with a temperature label of 10°C on the cup's surface. The surrounding temperature around the cup, displayed at all four corners, is also indicated as 10°C.

Energy transfer by heating

Thermal energy can be transferred from a hot object to a cooler one by conduction, convection and radiation.

A diagram illustrating the three methods of heat transfer using a cooking pot on a gas hob. The pot contains water with arrows showing upward movement representing convection. The handles of the pot are labelled "Conduction" with a red gradient, and orange waves going out from the flames below the pot represent "Radiation".

Conduction: Energy is transferred by direct contact

Convection: Particles with more thermal energy take the place of particles with less 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 comparison between a swimming pool and a kettle filled with boiling water.

Even though the swimming pool has a lower temperature than the kettle, the swimming pool has much more energy in its thermal energy store. This is because the swimming pool contains a much greater number of particles.

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