Here's why:

* Bimetallic strips are made of two different metals with different coefficients of thermal expansion. This means that one metal expands more than the other when heated.

* How they work: When the temperature changes, the bimetallic strip bends due to the different expansion rates of the metals. This bending action can be used to control a switch, turning the heating or cooling system on or off in a thermostat.

Let me know if you have more questions!