How to measure the distance covered by iphone during free fall?

Question

During the free fall the iphone is supposed to send acceleration values as 0 on all the three axis. So how to detect the distance covered by the iphone?

Answer 1

Ignoring air drag:

float t; // time since drop
float distance = 9.81f * 0.5f * t * t;

For greater distance (drop from airplane) you also could use the location services. CLLocation contains an altitude.