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

The special component you would need to use in a thermostat so that it can respond to changes in temperature is a bimetallic strip. Here are the steps explaining how it works:

1. A bimetallic strip is made of two different types of metal (such as brass and invar) bonded together. These metals have different rates of expansion when heated.

2. When the temperature changes, one metal in the strip will expand or contract faster than the other. This causes the strip to bend.

3. In a thermostat, this bending motion is used to open or close an electrical circuit. When the temperature rises, the strip bends one way and can turn off a heater. When the temperature falls, it bends the other way and can turn the heater back on.

4. This simple mechanism allows the thermostat to respond to changes in temperature and maintain a desired temperature level within a space.