Temperature

Temperature is intuitively associated with the sense of hot and cold. Put your finger in a pan of hot water and energy flows as heat from the water to your finger; you say that the water is at a higher temperature than your finger. Now put your finger in a glass of ice water and energy flows as heat in the other direction. The direction of energy flow as heat is the basis of our definition of temperature. Temperature is the property of objects—or more generally, systems—that determines the direction of energy flow as heat when the objects are put in direct contact with each other. Energy flows as heat from objects at higher temperature to ones at lower temperature. When energy as heat ceases to flow, the objects are at the same temperature and are said to be in thermal equilibrium.