Final answer:
Two objects not in thermal equilibrium will exchange heat until they reach the same temperature, thus achieving thermal equilibrium.
Step-by-step explanation:
Two objects that are not initially in thermal equilibrium will experience a transfer of thermal energy from the warmer object to the cooler one. This process continues until the temperatures of both objects reach equilibrium. Consider two objects, object X at a higher temperature, Tx, and object Y at a lower temperature, Ty. When they are brought into contact, the heat naturally flows from object X to object Y. This results in a loss of thermal energy for X and a gain for Y until the two objects achieve the same temperature and reach thermal equilibrium. In real-world applications, this principle is critical for understanding heat exchange between systems, such as cooling a warm beverage by adding ice.