Ebabil bir kustur (Ababil is a bird)

Today, without any apparent reason, I started murmuring an old song from a -- now not-existing -- Turkish band called "Grup Vitamin". The song's name is "Ebabil bir kustur" (Ababil is a bird).

http://www.youtube.com/watch?v=DaIJv02R4-s

Then, I realized that I have no idea what kind of bird "ababil" is. I searched google and found out that it is a swift, and in Turkish it is "dag kirlangici": http://en.wikipedia.org/wiki/Swift

Then, the question was how this word got into this song. More google search revealed that it is an Arabic word, and it has a famous story among Muslims. According to the story, an evil king tried to destroy Kabah in Makkah. God sent many gigantic flocks of swifts on the army of this king. Each bird was carrying chickpea-size baked-clay stones. They dropped these stones on the army and all army was killed.

OK, now how can a stone at that size kill a human? It has to be very fast when it reaches the ground, almost as fast as a bullet. How fast is a bullet?

http://hypertextbook.com/facts/1999/MariaPereyra.shtml

The speed of bullet, of course, depends on the gun and some other factors, but it looks like a bullet can be as slow as 200 m/s and can be as fast as 1500 m/s or more. Probably, 200 m/s is fast enough to cause fatal damage to a human.

If we get back to the stone story: Swifts can fly as fast as 60 m/s according to Wikipedia. Let's assume that just before leaving the stones, they flew vertically towards ground, giving  the stones an initial vertical velocity of 60 m/s. If they dropped stones from 200 m elevation, it would take about 14.7 seconds to reach ground level (according to basic free fall assumptions). In 14.7 seconds, the stone would gain about 147 m/s speed. If we add the initial speed of 60m/s, the final speed is 207 m/s. This is fast enough to be considered as "like a bullet".

Conclusion: Birds are dangerous.