Answer:
local stresses may exceed the limits of the glass
Explanation:
When hot water is applied locally to a portion of a glass vessel, it causes the immediate area to expand. That expansion stresses the region around the expanding area. The stresses may exceed the limit the glass can tolerate, so cause the glass to crack.
__
This was brought home rather dramatically when a strong stream of cold water was run into a glass container full of hot water. The bottom contracted and literally fell out.
