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In the given link of a video. The maker puts hot lava on different kind of types of glass .
my question is why does glass break into innumerable pieces rather than just cracking into two pieces or melting
As far as I understand glass is a bad conductor of heat and wont pass energy to all molecules within seconds so how does this happen
car glass has been chemically or thermally treated during its manufacture to contain large amounts of compressive stresses which tend to squeeze cracks in its surface shut, preventing the glass from breaking to pieces when struck or thermally stressed. when those residual compressive stresses are released (under sufficiently great stresses) the energy stored in the stressed glass is sufficient to break the glass into small pebbles which are less "dagger-like" than ordinary pieces of broken glass and hence less injurious during an accident.
This is why the different types of glass fracture in different ways.
