The reason why the glass burst is because of its expansion. As soon as hot water is poured into the cup, the inner wall of the cup expands sharply when heated, but the outer wall of the cup remains unchanged. The inner glass suddenly squeezed outward and the cup burst. If you heat the inside and outside of the cup at the same time in advance, and then pour hot water into it, the difference in expansion between the inside and outside of the cup is not so great that it will not burst. However, if ...10000.0000000105