Last night, in honour of National Science Week, we made things fall very slowly.
About a year ago we made a living room Gauss gun, and still have dents in the walls to prove it. Last night, using much the same stuff, we went for slowing things down rather than speeding them up.
The procedure is very simple, take a few rolls of aluminium foil and tape them together: We used duct tape and some bamboo skewers for stability. Then take a rare earth magnet or two and drop it down the tube. Then laugh delightedly when the magnets take an unexpectedly long time to pop out the other end. Our rough tests had the magnets falling at about one-fifth their normal speed.
What’s happening? Well this is down to one of those clever Germans – Heinrich Lenz who, in 1883, came up with a law of electromagnetic induction. Basically, the law says that when a current is induced in a conductor, a magnetic field is generated that opposes the action that produces the current. Dropping the magnet down the tube produces a current, thanks to the interaction of the magnetic field and the conductive aluminium, which in turn generates a new magnetic field that acts against the magnets and so slows their fall.
While I’d seen this done before with copper pipes in science museums, the revelation for me was that you could use a standard kitchen aluminium foil tube. It makes sense when you think about it, I guess I just hadn’t done that thinking.
This all works fine with just one roll of aluminium foil, but when you extend it out to three it becomes quite demonstrably spectacular. Next stop, six tubes and a ladder!
Now I’m perfectly well aware that this is not anti-gravity, but it’s feels like I imagine anti-gravity would. And it made for a much better title for this article than something about falling magnets, didn’t it?