Is it a good idea to shoot a gun in the sky, since what goes up (bullets in this case) must come down? I always wondered about this. I heard somewhere that this is a bad idea and that you might kill your-self (not good).

If you shoot the gun straight up (90 degrees) the bullet will stop at the apex of the trajectory. It will then fall at terminal velocity (The max speed an object can reach in freefall), and since it is very lightweight and also tumbles it won't have that much kinetic energy..

You'll probably get a lump on your head, but nothing more...

If you fire the gun at less than 90 degrees angle, the situation changes completely. The bullet will then have what is called a ballistic trajectory, and won't loose kinetic energy. It will infact gain kinetic energy once it has come to the top of its path, and starts to fall down again.

There has been many cases of those "Lost bullets" killing people miles away from where they were shot.. That's why many states in USA has a prohibition on fireing guns into the air.

Oh, thanks for answer.

This was tested some tine ago. It is, to date, the only myth to be busted, plausible and confirmed.