Flexibility!
Glass Fiber can dissipate energy along the fiber, normal glass does not have a structure to dissipate the energy in an even form and proves easier to crack as a result.
Similarly the...
As far as anyone can tell... yes. There has not yet been found an example of glass that is not glass.I say nay, glass is melted sand, so glass is sand.
Yes. Being made of plastic, a straw will float in water. The mass of the straw is typically designed so that it starts floating only after 3 quarters is inside the water and not before.