Pans warp due to thermal expansion and contraction. Hot spots in isolated areas cause that portion of the pan surface to expand greater than the surounding areas. And if you've never had a physics class to teach you such things, epansion due to heat can produce tons of pressure. Look at any long bridge, or even the highway. You'll notice that they have expansion joints built in. If they were constructed without them, the roads and bridges would crack.
It is also this uneven expansion that causes glass to shatter when it is forced to rapidly change temperature, as when you place a hot glass in cold water, or vice versa. The outside surface cools or heats more closely than does the inner structure of the glass. This causes enormous stress as the expansion or contraction takes place. And remember, glass is an insulator and takes time to transfer heat energy from the outside in.
The same is true of cast-iron. Though it is a contuctor, it is a poor one. It takes a relatively long time to heat upl, and to radiate its heat away as well, which is why its so good at searing and browning meats. But that's also why it cracks when immersed very into icy water. Also, cast iron is fairly brittle, for a metal.
Steel and aluminum are both more resilient than are either glass or cast iron. They tend to bend, or warp when uneven heat is applied. The reason the thicker steel and aluminum resist warping is that they have time to dissipate the heat energy more evenly than their tinner cousins, thereby avoiding uneven thermal expansion. It's like the difference between my sporting 30-06 rifle, and the old M-14 military rifle. They share similar calibers, and similar heat loads from the amunition. But my rifle has a relatively thin barrel. It is accurate for about three shots, and then begins to war slightly, messing up accuracy. The M-14, and its predecessor M-1, and for that matter, most any military rifel, have either thick, heavy barrels that resist warping under high temeratures, or heat dissipating devices attached to the barrels.
And rocks, well two things can cause them to explode; trappe water within the structure can heat and turn to steam. As it is trapped, it can build enough pressure to create a catastrophic failure of the rock struture, i.e., and explosion. The other potential event is that uneven thermal expansion. Like cast-iron, and glass, rocks are poor conductors of heat. Yet, they are subject to the same expansion forces as all other materials. They won't bend, and are brittle. Sounds like a recipe for a at last a crack or at worst a violent shattering, similar to an small explosion.
Well there you have it, physics lesson 231, the results of stress due to thermal expansion on materials, especially where cooking is concerned.
Seeeeeya; Goodweed of the North
