You have two identical looking metal bars. One of them is a magnet, with North and South ends. The other is simply an iron bar (which is attracted by magnets).

How can you tell which is which, using only these two bars?

Choose one of the bars and run the end of it along the length of the other bars a number of times.  If the bar you chose is the magnet then it will create a magnet of the other bar and you will have two bars which can repel each other.  If the bar you chose is not the magnet then it will have no effect on the other bar and you will still have two bars which appear to attract each other (even if you place the end of one up to the centre of the other)

Posted by Fletch on 2005-01-25 15:30:29