which special component would you need to use in a thermostat so that it can respond to changes in temperature?

The special component needed in a thermostat to respond to changes in temperature is typically a bimetallic strip or a temperature sensor such as a thermistor or thermocouple. A bimetallic strip is made of two different metals laminated together that expand at different rates when the temperature changes, causing the strip to bend and mechanically activate a switch to control heating or cooling systems. This strip responds directly to temperature changes and adjusts the thermostat accordingly. Alternatively, electronic thermostats often use temperature sensors like thermistors (which change resistance with temperature) or thermocouples (which produce a voltage depending on temperature differences) to detect temperature changes and electronically regulate the system. In summary, the key component that allows a thermostat to respond to temperature changes is the temperature-sensitive element, most commonly a bimetallic strip in mechanical thermostats, or electronic sensors like thermistors or thermocouples in modern thermostats.