What is temperature?

Temperature is a measure of the internal energy of a system. Internal energy is kinetic energy associated with the motion of atoms, molecules, and electrons making up the system.

What is heat?

Heat is energy transferred between a system and its surroundings because of a temperature difference between them. Heat naturally flows from higher temperature to lower temperature.

What is the connection between them?

The First Law of Thermodynamics links temperature (via internal energy), heat, and work. Adding heat generally corresponds to an increase in temperature, although not always. Examples of exceptions include:

• If all the heat goes into doing work, the temperature will not change.
• During a change of state the internal energy increases without any change in temperature.