Take 10 rare-earth magnetic spheres and assemble them into a chain. Then, holding the chain vertically over the disk magnet, slowly bring it toward the scale. (You’ll probably need two hands to hold the chain straight, as it will try to veer away.)
> Notice that, if you hold the chain one way, it’s attracted to the disk magnet (click to enlarge the photo and diagram below). If you flip the chain over and hold it the other way, it’s repelled. Since most scales won’t properly measure negative values, you’ll get better measurements if you hold the chain of magnets so they repel the magnet on the scale. (If your digital scale is okay with negative values, though, you can use the stack either side up.)
Hold the chain vertically over the scale and watch the reading as you slowly move the chain closer to the magnet, and then farther away. You’ll see that the reading varies with distance. Because of this variation, you’ll want to have each chain the same distance over the scale as you work, so you can make comparisons with other arrangements.
For consistency, place the chain so that it just touches the marked spot on the plastic container. Hold the chain in place, and record the reading on the scale (see photo below).
Pull the chain apart so it’s only half as many spheres (5, rather than 10). Set this short chain in place above the magnet, as you did before, and record the reading on the scale. Surprised? The new reading isn’t half the original reading. Play with the length of the chain. What do you notice?
Rebuild the chain so that it’s 10 spheres long again. Then fold the chain in half. (It might spontaneously become a circle; if so, just squash the chain flat so it forms a double line 5 spheres long and 2 spheres wide. Click to enlarge the photos and diagram below.)
Bring this new chain near the scale and record the reading, as shown in the diagram below. Are you surprised by the result?
Let’s try something that’s similar but not quite the same. Make the 10-sphere chain again, and then split it into two 5-sphere chains (see diagram below).
Bring the a-e chain towards the f-j chain so that sphere a is near sphere f. As the chains get closer, you’ll see them bend away from each other, as shown in the diagrams below.
Keep bringing the chains together. Once the two chains are close enough, you’ll be able to see them snap into place, with one chain offset from the other chain, as shown in the diagram below.
Bring this pair of chains near the scale and record the reading (see diagram below). How does it compare to the reading for the folded-over chain? How are these two chains different?