Thermal Equilibrium

Thermal equilibrium is the condition two objects reach when heat stops flowing between them. Picture a piece of ice dropped into a glass of water at room temperature: heat flows from the warmer water into the colder ice, the ice melts and the water itself cools slightly, and after enough time the two settle to a shared, unchanging temperature. Mix hot water and cold water together and the same thing happens — heat flows from the hot portion to the cold portion until a single common temperature is reached. …