Question

Why does a glass tumbler sometimes crack on pouring very hot tea?

Answer 1

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.

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Answer 2

the crack is caused by different thermal expansion. the part of the glass that the boiling water touches first expand due to 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 sometime too much and break the glass