Question

Why does glass tumbler breaks when we pour hot water in it

Answer 1

Glass comes in the insulator class of material which means it is a poor conductor of heat,when you pour a very hot liquid into a thick tumbler what happens is, the surface of glass that comes in contact with the hot liquid heats up and expands as per its coefficient of thermal expansion, while the outer layer still remain cold and does not expands (because glass is a poor conductor and does not carry heat quickly). This leads to development of thermal stresses which eventually causes cracking.

Detail Explanation :

Glass tumbler break due to the difference in thermal expansion of their inner and outer surfaces.Glass is known as a bad conductor of heat.Hence when the tumbler is suddenly filled with hot water,the inner layer of the glass gets heated immediately as it comes into contact with hot liquid.But the outer layer remains at a lower temperature for some more time as the heat is conducted through the glass only slowly.

As a result,the inner layer tends to expand more than the outer layer.This leads to cracking.Thick-walled tumblers and tumblers made of special quality glass withstand such cracking to a certain extent.