Nearly every material, whether it is solid, liquid, or gas, expands when its temperature goes up and contracts when its temperature goes down. This property, called thermal expansion, makes a hot air balloon float, and the phenomenon has been harnessed to create thermostats that automatically turn a home furnace on and off. Railroads, bridges, and buildings are designed with this property in mind, and they are given room to expand without buckling or breaking on a hot day. Thermal expansion occurs because a material's atoms vibrate more as its temperature increases.

https://www.miragenews.com/caltech-reveals-why-certain-alloys-resist-heat-1055419/

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