Temperature is directly proportional to the average kinetic energy of the molecules in a substance. If the degree of motion of the molecules inside an object doubles, the temperature will also double.
Temperature is used as a measure for heat in an object by measuring the amount of kinetic energy in the molecules that make up the object. A cold object will have molecules which move very little. When heat is supplied to a cold object, the energy of the molecules in the object increases. This is because heat is a form of energy that can be transferred from the heat source to the molecules, and it can also change its form from heat to movement. The molecules that have gained extra energy will have a higher tendency to move more than the molecules that have not gained the extra energy. Energy of motion is called kinetic energy. When the molecules move or vibrate more, they have a higher kinetic energy, and this is recorded as an increase in temperature.
While on most occasions, supplying heat to an object results in an increase in temperature, there are exceptions to this rule. When the heat supplied causes a phase change in the object (melting, boiling, condensation or freezing), all of the heat energy is used to rearranging the molecules into the new phase. During phase change, change in kinetic energy does not result in a change in temperature.