Magnetizing a Nail

why must a nail be stroked in the same direction and same pole?will the number of strokes affect the strength of the magnet?
- isabelle (age 10)
Singapore

One part of the question you can answer yourself. Take a nail and stroke it with a magnet, then measure how magnetic it is. Keep doing that and you'll find out how the magnetism changes with number of strokes. But how can you measure the magnetism of the nail? One way would be to hang it by a thread near another nail that isn't magnetized. The stronger the magnetization is the more you'll see the two nails pull toward each other. Another way would be to see how far the nail could be from a little compass and still turn the compass needle some amount- say 30°.

Now if you switched poles used to stroke the nail, the opposite pole should magnetize the nail the opposite way. Whatever the North pole does, the South pole does the opposite. That would end up cancelling and giving very little magnetization. You can try alternating poles and see if that prediction is right. 

I'm not sure what effect the direction of stroking has. My guess is that if you stroke with a North pole it tends to make the bail's South pole in the end you're stroking toward. Then if you alternated stroke directions, you'd get the same sort of cancelation that I bet you'll find alternating poles. But the experiment will tell you the real answer.

Here's another question you can test: what if you alternated both poles and directions? Say you stroked North toward the nail point and then South toward the nail head, alternating? Again, you can do the experiment.

We'd love to hear the results.

Mike W.

(published on 07/06/2015)