Q. Why is a glass broken, when hot water is poured into it?
A. Because the inside of the glass is expanded by the hot water, and not the outside; so the glass snaps for want of flexibility.
Q. Why is not the outside of the glass expanded by the hot water, as well as the inside?
A. Glass is a non-conductor of heat; and, therefore, breaks before the heat of the inner surface is conducted to the outside.
Q. Why does a glass snap, because the inner surface is hotter than the outer?
A. Glass is expanded by heat; and as the inner surface expands, it stretches the outer surface till it snaps.
Q. Why is a china cup broken, if hot water be poured over it, or into it?
A. China is a non-conductor; and, as the inner surface expands by the heat, before the outer one, it forms an arch, and pulls the parts of the cup asunder.
Q. Why does the bottom come off, if a glass beaker be set on a warm hob?