Libyan rebels are rejoicing in Tripoli by firing their guns in the air. Little do they know, this is one of the dumbest ways they could celebrate.
It all comes down to our good friend gravity. When a bullet goes up, it must come down and you have little control where it's going to land. Though a falling bullet is estimated to have only 10 per cent of its original muzzle velocity, it still has a good chance of injuring and possibly even killing you.
A 30-calibre bullet falls at 322km/h, while a 50-calibre falls at almost 531km/h. And that's why they kill people. A bullet falling at as little as 170km/h can pierce the skin, while one falling at 217km/h can travel through your skull and into your brain.
Even if the bullet falls at a rate somewhere between 160km/h and 217km/h, it still can knock you on the head and give you a traumatic brain injury. Of course the bullet can miss your head, but it could hit you in the arms, shoulders, and legs. Ouch. [Amazing Facts and The Straight Dope]