Summary

Temperature is an indicator of the presence of thermal energy: when the temperature of an objects increases, energy has been added to it.

Many physical properties depend on temperature. The most common kinds of thermometers make use of thermal expansion.

Objects placed in contact will exchange energy, and when isolated from other sources of energy will come to have the same temperature.

The important ways to move thermal energy from one place to another are

It takes energy to cause a change of phase (solid into liquid, or liquid into gas), without having any change in temperature at all. The amount of energy is large compared to the amount of energy required to change the temperature of the object by a few degrees. Assuming that there is no change of phase involved, the amount of energy required to change the temperature of an object is proportional to the amount of stuff in the object (mass or number of atoms), and to the change in temperature. It also depends on the substance of which the object is made.

There are two fundamental laws of physics governing heat: