The $g$-force of common objects hitting the floor At my friend's work they have an accelerometer which measures the force with which certain objects hit the ground. He claims that from four feet high, cell phones hit a solid metal surface with a $g$-force of over 2000. Is this right? It seems like that number is way too high.
I understand that $g$-force is calculated by (acceleration in m/s2)/9.8. I suppose if an object instantly decelerates it would have a very high $g$-force. However, is 2000 a legitimate number? It just seems extremely high.
 A: updated calculation
As a rule of thumb the "g force" of an impact is the ratio of the distance of the fall, and the distance it took to stop falling. This is based on a simple work done argument - $F_1\Delta x_1=F_2\Delta x_2$, and of course $F=m\cdot a$. This approach is the same as used in this article describing a 'bubble wrap drop' Mythbusters experiment. There may be a factor 2 there depending on whether you assume a constant decelerating force (crushing bubble wrap) or an elastic deceleration (where force increases with displacement).
I estimate that when a phone drops on a hard surface, it distorts by about 0.2 mm - based on observation of the small dent on the corner when my wife did in fact drop her phone. But see video below for a much larger distortion...
Taking the ratio $\frac{1200 mm}{0.2 mm}\approx 6000 g$ - meaning that your 2000 g is a reasonable number.
I found a slow motion video of an iPhone breaking - it shows that the distance over which it moves / distorts is significantly greater than I estimated so the g forces will be less:

Source of image
When you put your iPhone in a case that provides even a couple of mm of "give" during a drop, the g forces will be much lower and you will improve the chances of surviving a drop on a hard surface very significantly.
A: using an accelerometer app I saw that dropping you phone onto a blanket only makes the phone hit like 6 to 8 g's and it doesn't cause harm. Humans in fighter jets widthstand these forces also without harm so it makes sense that it would takes thousands of g's to break it. 
