Bimetal

Metal 1 expands more with higher temperature than Metal 2. Connecti them together and heating forces the bimetal to bend.

Bimetal means two different metals joined together. Instead of being a mix of two or more metals, like alloys, bimetallic objects are made of layers of different metals.

Bimetallic strips move when they are heated up. They are the most common bimetallic objects. They are often used in electric kettles as a temperature switch.