Basic science

Heat is a form of energy that is transferred between objects of differing temperatures. It is measured in joules.

Temperature is a measure of the average kinetic energy of the random movement of molecules within a substance. It quantifies how hot or cold a substance is, and gives an indication of how likely a substance is to transfer heat energy. Hot objects contain molecules with a higher average kinetic energy and will transfer this energy to cooler objects. The rate of energy transfer is dependent on the temperature gradient and thermal conductivity of the objects involved.

The SI unit for temperature is the kelvin (K), which is defined as 1/273.16 of the thermodynamic temperature of the triple point of water. The triple point of water is where ice, water and water vapour exist in equilibrium at a pressure of 611.2 pascals. Other commonly used scales are the Celsius and Fahrenheit.

There are four laws governing thermodynamics that describe how heat energy and other forms of energy are related.

The zeroth law of thermodynamics states that if two thermodynamic systems are each in thermal equilibrium with a third system, they are all in thermal equilibrium with each other.

The first law of thermodynamics states that in a closed system the total quantity of energy remains constant, as energy cannot be created or destroyed. Shivering generates heat from kinetic energy, which is generated from chemical energy within muscles. This is an example of the mechanical equivalent of heat concept.

The second law of thermodynamics states that the entropy of the universe (as a closed system) will increase over time. Entropy is a measure of disorder within a closed system. This is why heat is transferred from hotter to colder objects and not the other way round.

In the third law of thermodynamics, the entropy of a perfectly crystalline compound is zero at absolute zero. At absolute zero (0 K or –273.15°C), no thermal energy exists.