Riddle: If boiling water is poured into a thick drinking glass as well as a very thin wine glass, of the two, which is more likely to crack?
Answer: The thick glass is more likely to crack since glass is a poor conductor of heat. In a thin glass, the heat passes more quickly from the glass into the surrounding air, causing the glass to expand equally. When hot water is poured into a thick glass, the inner surface expands, but the outer surface does not. It is this extreme stress on the glass that causes it to crack.