There are several equivalent definitions of temperature. In thermodynamics, temperature is defined as a property of an object that determines the direction of heat flow. Heat always flows from a higher temperature region to a lower temperature region. Heat flow stops when the two regions reach an equilibrium state, called thermal equilibrium. Two objects are said to be of the same temperature if they are in thermal equilibrium. This is also called the 0th law of thermodynamics. This definition only gives a comparison between the temperatures of two objects. In statistical physics, the temperature can be defined without using comparison between two objects. Simply speaking, the temperature is a quantity proportional to the internal energy of an object. Internal energy is defined to be the sum of the kinetic and potential energy of all the molecules inside the object. Internal energy is difficult to...