18.1 : Temperature and Thermal Equilibrium

Heat and temperature are essential concepts for everyone every day. The study of heat and temperature is part of an area of physics known as thermodynamics. It is not always easy to distinguish heat and temperature.

The concept of temperature has evolved from the common concepts of hot and cold. The scientific definition of temperature explains more than just our sense of hot and cold. Temperature is operationally defined as the quantity measured with a thermometer. Furthermore, temperature is proportional to the average translational kinetic energy, which provides a more physical definition. Differences in temperature maintain the transfer of heat throughout the universe. Heat transfer is the movement of energy from one place or material to another as a result of a difference in temperature. The transfer of heat can change the temperature, and it will affect everything from the behavior of atoms and molecules, to cooking, to the weather on Earth, and to the life cycles of stars. One can feel heat entering the body from the summer Sun or from hot coffee or tea after a winter stroll. One can also feel heat leaving the body from the chill of the night or the cooling effect of sweat after exercise.