Les Jones

Science > The Blogosphere's Rockin' Physics Fun Zone

A while back Uncle posted this:

Junior has one of those Magna Doodles that has three pieces with one side of a magnet exposed (square, triangle, circle) for imprinting shapes onto the Magna Doodle. I take two magnets each of which only has one side exposed and the other side is covered by plastic (we’ll say circle and square) and they stick together. I conclude that one exposed side must be positive and one exposed side must be negative. However, I touch both exposed sides to the triangle separately, and they both stick to it. This had me understandably puzzled.

Is there some new kind of gay magnet or something?

So we haven't bought any Magna Doodles, but we bought Katie some magnetic letters for the refrigerator. I was noticing the magnets on the back, and thought of Uncle's post. The magnet is actually two bar magnets attached end to end, presumably at opposite poles.

When I put the magnets from two letters together, they always stick. There's a repulsion at some points, but they always settle into an attractive state, because within a few millimeters there's a pole they find attractive. I'm guessing Magna Doodles use a similar trick.