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• Solid State Physics

# Why does glass crack in the freezer?

Wiki User

2013-02-07 15:27:28

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Glass is a brittle solid. The characteristic "brittle" means that if you apply force, it breaks (cracks) before it bends much.

There are two reasons a glass container may break when it changes temperature.

1. If the glass object contains a solid that changes size with temperature so that it becomes larger in size in size than the glass container, it exerts a force on the glass and if the force is large enough, the glass will break. Here is a discussion of that.

In reality, no the glass will not crack unless you have stored something inside that will expand (water based) when it freezes. It is not the temperature that cracks the glass, more the expansion of the contents will exert great pressure on the walls of the container.

A non-messy example can be made simply but filling a small plastic (not brittle) bottle to the brim with clean water, adding a lid and then freezing it. You will find the ice will have made the bottom of the container bow out (or possibly break) as a result of the increased volume ice has over water.

If you take a jam jar, fill it with water to the brim and place a lid on then freeze it, the jar will crack. If however you fill it with a substance that will either not freeze or is not water based (so doesn't have the expansion issue that water does when it turns to ice) then the jar will be fine.

2. Glass, like most materials, changes size when heated or cooled. If a glass object is heated or cooled so the temperature is different in different parts of the object, then the different parts of then a stress is created because the object is being stretched in a nonuniform fashion. Stress is a force. Strain is the distortion due to the force. If the object is brittle, then nonuniform strain will cause it to crack.

In practical terms that means that brittle objects can will crack unless heated slowly so that temperature is nearly uniform and strain is small.

That is also why the kind of glass used in cooking is different than the kind of glass used for holding liquids. Some forms of glass are more brittle than others.

2013-02-07 15:27:28