We can all remember that one time (probably more) when you dropped your phone.
I'm probably most guilty of this crime against technology, and I'm always covering up my valuables with the giant bulky cases that could probably stop bullets. But how do these work?
When your phone falls and hits the ground, the impulse is dependent on its mass and velocity. Since velocity increases the further the phone falls, a greater distance means a greater impulse. That's why it's safe to drop your phone on a table, but not the driveway.
The surface of the ground also plays a part. A phone falling a few feet onto tile is sure to shatter your screen, but you'd have a better chance of it surviving a fall onto your bed. This is because a harder surface stops the phone much quicker, and so it feels less of the impact. This is also why putting a case on your phone can make it live much longer.