You have a bar magnet who'se poles are not marked. How can you find which poles is no and which is south by using only a piece of string?

One way to determine which pole is north and which is south on an unmarked bar magnet using only a piece of string is to suspend the magnet from the string so that it can freely rotate. The magnet will align itself in the north-south direction due to Earth's magnetic field. The end of the magnet that points towards the geographic north pole is the north pole of the magnet, and the end that points towards the geographic south pole is the south pole of the magnet.

1. Tie the string to the center of the magnet.
2. Suspend the magnet from the string so that it can rotate freely.
3. Wait for the magnet to stop rotating.
4. The end of the magnet that is pointing north is the north pole. The other end is the south pole.