Question

thick walled glass tumbler frequently cracks if hot water it is poured into it

Answer 1

This is all because glass is bad conductor of heat i.e. Heat can't be able to pass through the glass easily.

It's quite easy .Here the inner surface of glass expands more than compared to outer surface,since inner surface is direct in contact with warm water.

Since unequal expansions take place in same body simultaneously causing it to be unstable i.e. crack.

Hope you got it.

Thanks !!!