On the BBC panel game QI last night (4th May) the contestants built electric motors, (or at least spinning rotors) using the sole components of ; a short length of wire, an AA battery, a large woodscrew, and a small round magnet.
I've tried it myself, and it really works - but how?
The screw always rotates in the same direction, and is self starting. The wire in contact with the magnet is clearly acting as a commutator, and the field lines produced by the permanent magnet and the current passing through the screw must provide the motive power, but I can't see how.
Try it yourself - place the magnet on the head of the screw, suspend the screw point uppermost from one end of the battery (you need a powerful magnet, about the same size as the screw head), then use the wire to connect the other end of the battery to the side of the magnet.
While you are at puzzles anyway, would anybody help me explain a friend why planes flying against the rotating of the Earth have to fly forward at all - he claims they could get off and stay up there until the Earth turns the destination right below them.
could get off and stay up there until the Earth turns the destination right below them
If they could do 1000mph (approx, at the equator) they would. They would be doing 1000 mph relative to the earth's surface while the earth was spinning at the same speed the other way - i.e. the plane would be standing still relative to an observer out in space.
Speed would need to be less at different latitudes.
Actually, thinking about it, I don't believe it is Fleming's left or right hand rule, but actually Maxwell's corkscrew rule that makes it work.
Incidentally, there's no need to use a screw, a small symmetrical Yale type key works well. The best visual effect I've found is to use a large keyring with a small ball-bearing on top to reduce friction.
Location: Dublin, Ireland. (No, I just live here.)
Posts: 654
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Originally Posted by probes
While you are at puzzles anyway, would anybody help me explain a friend why planes flying against the rotating of the Earth have to fly forward at all - he claims they could get off and stay up there until the Earth turns the destination right below them.
Because planes fly against the air, and the air is generally following the rotation of the earth. It doesn't do so perfectly, of course, and when it doesn't, that's what we call "wind". If planes went above the atmosphere, as satellites do, that would be a different matter entirely.
While you are at puzzles anyway, would anybody help me explain a friend why planes flying against the rotating of the Earth have to fly forward at all - he claims they could get off and stay up there until the Earth turns the destination right below them.
How big a conveyor belt would he need to try it, can try to knock one up out of wood, fairy liquid bottles and sticky-back plastic tomorrow......
but actually Maxwell's corkscrew rule that makes it work
Touche! Actually it's the magnetic field that makes it turn, and you could call that Marjorie or Derrick and it would still work.
Quote:
While you are at puzzles anyway, would anybody help me explain a friend why planes flying against the rotating of the Earth have to fly forward at all - he claims they could get off and stay up there until the Earth turns the destination right below them.
has he tried jumping into the air to see how much the earth turns before he Lands?
Question: in order for it to rotate, does the Elephant have to lie on his back and sort of juggle with his feet ? If not and the Elephant remains upright, I don't see how it can rotate at all.
Desert Dingo's Video above says "Build a Simple Electric Motor in 5 minutes. Why is it a 17 and a half minute video?
