Heat is the transfer of thermal energy between objects that have different temperatures. Thermal energy always moves from an object with a higher temperature to an object with a lower temperature. When thermal energy is transferred in this way, the warm object becomes cooler and the cool object becomes warmer. Sooner or later, both objects will have the same temperature. Only then does the transfer of thermal energy end. Assume that a cool spoon is placed in a cup of steaming hot coffee. Once in the coffee, the spoon quickly heats up. The fast-moving particles of the coffee transfer some of their energy to the slower-moving particles of the spoon. The spoon particles start moving faster and become warmer, causing the temperature of the spoon to rise. Because the coffee particles lose some of their kinetic energy to the spoon particles, the coffee particles start to move more slowly. This causes the temperature of the coffee to fall. Before long, the coffee and spoon have the same temperature.

Questions

How is heat defined in physical science?
Describe how thermal energy is transferred.
When does the transfer of thermal energy end?