You’ll know when it’s over.
Upon impact, a small amount of elastic energy is converted into acoustic energy — that resounding indication of breaking glass. But the majority of the elastic energy stored in the glass will be converted into two — or more — new surface energies. A crack. Or several cracks. With one eye closed, you’ll reach down gingerly, reluctant to turn it over. There won’t be any shards to pick up off the pavement, only a phone with a freshly splintered screen, the jagged lines and spiderwebs forming some kind of painful abstract art.
You’ve just smashed your phone’s screen.
The glass layered on the front of your phone is a lot of things: thin, flexible, transparent. But the only two things that matter when you drop it are its hardness and its strength. Hardness is resistance to abrasion. It’s your screen’s first line of defense against car keys, kitchen tables and concrete. Strength is the relationship between the surface compression and inner tension; it determines, among other things, how many blows a piece of glass can endure before it shatters completely. Glass only breaks in tension, when the force of impact finally overcomes the surface compression. A scratch doesn’t shatter glass, but small stresses will eventually lead to a colossal splintering.
