You have four metal bars. When bar 1 is placed in a line with each of the other three bars, the force between them is attractive. If bar 2 or bar 3 is flipped over, the force between each one and bar 1 is still attractive, but when bar 4 is flipped over, the force between bar 1 and bar 4 is repulsive. When bar 2 and bar 3 are placed in a line with each other, the force between them is attractive, and when one is flipped over, the force is still attractive. Which of the bars are permanent magnets? Explain the source of the attraction for each of the following sets of bars: bar 1 and bar 2, bar 1 and bar 4, bar 2 and bar 3.

You have four metal bars. When bar 1 is placed in a line with each of the other three bars, the force between them is attractive. If bar 2 or bar 3 is flipped over, the force between each one and bar 1 is still attractive, but when bar 4 is flipped over, the force between bar 1 and bar 4 is repulsive. When bar 2 and bar 3 are placed in a line with each other, the force between them is attractive, and when one is flipped over, the force is still attractive. Which of the bars are permanent magnets? Explain the source of the attraction for each of the following sets of bars: bar 1 and bar 2, bar 1 and bar 4, bar 2 and bar 3.