Question

Why does a glass tumbler sometimes cracks when hot tea is poured into it
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Answer 1

Answer:

The crack is caused by differential thermal expansion. The part of the glass that the boiling water touches first expands due to the heat, but the heat doesn't conduct through the glass quickly so there is stress between the expanded inside of the glass and unexpanded outside of the glass. This stress is sometimes too much and the glass cracks.

Explanation:

Answer 2

Explanation:

When boiling water is poured into a thick tumbler its inner surface expands. However, due to low thermal conductivity of glass, the expansion of outer surface of the tumbler is quite small. Due to uneven expansion of the outer and inner surfaces, the tumbler breaks.