Pushing and Pulling: Does Placing Magnets Together Always Increase Their Combined Magnetic Attraction?

Problem

Does placing magnets together always increase their combined magnetic attraction?

Materials

• 2 large sewing needles
• bar magnet
• scissors
• ruler
• sheet of paper
• compass

Procedure

1. Lay the two sewing needles on top of the magnet, with the eye of each needIe pointing toward the south pole of the magnet.



2. Allow the needles to remain on top of the magnet for at least one minute.
3. Remove the needles and insert the pointed ends through a piece of paper measuring 4 inches × 4 inches (10 cm × 10 cm). The needles should be as close as possible and the ends even and pointing in the same direction.
4. Lay the compass on a wooden table, with the needle pointing toward the N printed on the compass face.
5. Hold the paper containing the two needles near the side of the compass marked with a W.
6. Observe any motion in the compass pointer.
7. Reverse the direction of one of the needles, so that the needles are close and the eyes point in opposite directions.
8. Again hold the paper containing the two needles near the side of the compass marked with a W, and observe any motion in the compass pointer.

Results

The compass pointer moves toward the ends of the sewing needles when their eyes are together. The compass pointer moves only slightly or not at all when the eyes of the needles are facing in opposite directions.

Why?

Placing the needles on the bar magnet causes the atoms in the needles to line up in a north-to-south direction. The needles become magnetized; their eyes become south poles, and their pointed ends become north poles. laying the needles with their eyes pointing in the same direction puts the needles in a parallel position (with "like" poles together at each end). Both of the magnetized tips of the needles pull on the compass pointer. Combining the strengths of the two needle magnets in the parallel position produces strong force on the compass pointer. Reversing the direction of one of the needles places the magnets in an antiparallel position (two "unlike" poles, a north pole and a south pole, together). Unlike poles work against each other; one is pushing while the other is pulling on the compass pointer. The result is the same as using a weak magnet or no magnet at all.

Let's Explore

1. Would laying the two sewing needles on top of a bar magnet with the eye of each needle pointing toward the north pole of the magnet affect the results? Repeat the experiment, this time positioning the needles so that the eyes both point toward the north end of the magnet.
2. Would other magnetized materials produce the same result? Repeat the original experiment using iron nails instead of needles. The nails could be held together instead of inserting them through a piece of paper.

Show Time!

Use a pencil, three or four round magnets with a hole in the center, and iron filings to measure the strength of magnets in parallel and anti parallel positions. Place the pencil through the holes in the magnets. Support the bottom magnet while standing the point of the pencil in a mound of iron :filings. Slowly lower the magnets until the iron filings begin to move. Perform the experiment with the "like" poles pointing in the opposite direction from each other. The repulsion between the magnets will cause them to float apart. Push the floating magnets together, or as close as possible, with your fingers and slowly slide them down the pencil toward the iron filings. Repeat the experiment with the magnets in an opposite position ("unlike" poles facing each other). The magnets will cling together and be easily lowered toward the filings. Diagrams and photographs of the experiment can be displayed. Display models by supporting the ends of the pencils in clay. Which is stronger? Why?

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Janice VanCleave's Magnets
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