Why Does Iron Bend When it is Hot?
We all know that things vary in the way they behave when something tries to alter their shape. Some things will rather break than bend; others will bend and then come back again to their old shape; yet others after bending will stay in the new shape. Various names are applied to these different properties of matter. A general rule that applies almost always is that the colder a thing is, the more rigid it is. This applies even to the three great states of matter, solid, liquid and gaseous; for it is only in the coldest of these - which is the solid state - that things can have any rigidity at all, and, as a rule, the colder a solid thing is. the more rigid (unbending) it becomes. We believe that when a thing is made hot, the molecules of it are thrown into a state of greater motion, and we know that they are farther apart, for the thing expands. But if the molecules are farther apart, and if they are moving about more violently, they can not be holding on to each other so tightly and rigidly as before, and so the thing which, when it was cold, could not be bent, can now be bent. Directly we understand the nature of heat, we see how reasonable it is that iron should behave as it does.
