Final answer:
In the calorimeter example, Option 1; metal loses heat to the water until both substances reach thermal equilibrium. This principle occurs as heat flows from a hotter object to a cooler one.
Step-by-step explanation:
In the calorimeter setup as described, when a hot piece of metal is placed into cool water, heat will transfer from the metal to the water. This is because heat energy naturally flows from a substance at a higher temperature to one at a lower temperature until thermal equilibrium is reached. In this case, the component losing heat is the metal (Option 1). The water will gain the heat lost by the metal, leading to an increase in water temperature. Eventually, the metal and the water will reach the same temperature if the calorimeter does not allow for heat exchange with the environment. This ensures the net heat change remains zero, with the caveat that this is an ideal scenario.