Recently I saw a commercial for a phone that said that the screen of this phone could not be cracked. This got me thinking of all the stories that people have told me about their phone cracking and what truly causes this to happen. A few times I have dropped my phone and assumed that when I picked it up it would be completely shattered, but I was wrong. Why is it that a phone can shatter on a short fall, while other times it sounds as if it were hurled at the ground and it ends up without a scratch on it?

That question can simply be answered with luck. The likeliness of a phone to crack is dependent on where on the phone makes initial contact with the ground. If the phone falls directly on the face it is not very likely to crack because the impact is spread throughout the whole surface of the face. If a phone is dropped on its corner, the force of contact with the ground is much more concentrated in one area, making it more likely that the glass screen will not be able to survive the fall. A phone that falls from a short height and lands on its corner is more likely to crack than a phone that falls from a greater height and lands directly on the face. 

The strength of a phone screen is dependent upon both the surface compression and inner tension of the phone. This strength determines how many blows the screen can take before shattering. Glass only shatters if the force of an impact is greater than the surface compression. So if a phone is only dropped from a short height, it is not likely that it will contact the ground with enough force to shatter the screen. You can't really measure the exact strength of a piece of glass because that is dependent upon the makeup of the glass, but you can get a pretty good idea of how strong a glass phone screen is. 

The likeliness of a phone to shatter is also dependent on the surface that it lands on. It seems obvious, but a phone is more likely to crack on concrete than on a pillow because there is a greater force applied to the phone upon impact when it hits the concrete rather than the pillow.

So if you ever drop your phone and are worried as it falls through the air that it is going to crack, just hope that it falls directly on its face. Or, better yet, buy a good case for your phone. That way you won't have to worry so much about the ability of your phone to take the force of impact with the ground.