Useful Applications of Thermal Expansion

Physics is not just for the scientists. There are many applications of physics the the lest scientific among us, many of them making our lives much easier.

Glass is a much used material in the kitchen. Glasses and jars are often made from them, and they are often used with hot liquid. Care must be taken however. Glass is brittle and a very poor conductor. If a hot liquid is poured into a cold glass jar, the inside will expand, but heat will not be quickly conducted to the outside surface of the jar so that it can expand. The result may be that the jar cracks. Cracking can be expanded if the jar is slowly heated in an oven. Heating will be more more even and the jar can expand with less strain.

Many items of cookware are made from types of glass with very low thermal expansivity – pyrex and pyrosil. They expand by a small fraction of the amount that ordinary glass expands to when heated so that strain throughout the material is less. These items may be plunged from a hot oven into cold water without cracking.

Glass stoppers in glass bottles or glasses stacked inside each other may become tightly fixed. The tops on jars may be screwed on overtight and become impossible to remove. Increasingly warm water may be poured over the outside of the bottle, the outside glass, or the overtight lid. The stopper/glass/top expands more than the stopper/inside glass/top and become much easier to reomve.

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