Why does your phone screen crack from the slightest fall but stay intact when dropped from 1000 feet? Check out the video above for the scientific answer.
Every smartphone owner has felt terror grip their soul whenever their phone slips from their hands and smashes against the pavement. And for good reason, modern phone screens have the unfortunate tendency to break quite easily. But how was a man able to drop his mobile phone from an airplane last year without a scratch on it? Allow us to explain.
A 1000 foot fall
In August 2017 pilot Blake Henderson lost his phone while pursuing a biplane in the sky. The aircraft kept track of the entire fall (from about 1000 feet above sea level) up until the moment it was found by a man in his yard. To his surprise, the pilot was able to recover his smartphone intact, a feat all the more impressive since we know the propensity for phone screens to break at the slightest impact.
A screen under tension
The outcome of the fall does not solely depend on altitude explains Peter Houk, director of an M.I.T laboratory dedicated to the study of glass to the website Livescience. The surface on which the phone lands, as well as the angle of the fall also play a role in how the screen is affected by the impact.
Glass is a material that can withstand high compressive forces, which is why a phone that falls flat on its screen usually withstands any damage. However, if glass can easily withstand that kind of pressure, it’s a different case when it comes to tension. Just try folding a glass plate in half to see (don’t try this at home of course).
A glass like no other
In order to remedy this, the glass used to cover phone screens, the same kind used for car windscreens and window panes, is not the same as the kind used for a jar of mustard for example; it is known as tempered glass. The glass goes through a chemical or thermal tempering, which gives it increased strength and, in case of breakage, causes it to shatter into several small fragments which are not dangerous, instead of long, sharp blades (as seen in the video).
For smartphones, manufacturers often use Gorilla glass, a glass chemically toughened in potassium salt baths, a technique that according to Houk makes it particularly strong and resistant to scratches. However, it is difficult to make glass completely devoid of flaws, and this material also does not have the crystalline makeup which gives a diamond its strength for example.
The result is if your phone falls on its edge or on one of its corners, the pressure builds up and these small imperfections can cause the glass to reach a breaking point. The risk of breakage is greater if the phone falls on a hard and irregular surface. This is how Blake Henderson’s phone survived a fall of more than 1000 feet, by falling at an angle that limited the risk of a pressure build up, onto the soft surface of a stranger’s lawn.