Linear motor with permanent magnets. Where is the sticky point?

  1. Hello, recently I have found this diagram
    Also seen some videos on youtube.
    If this really work in moving a magnet linearly, the first thing that someone may think is why not to combine this linear motor into a circle, to move a magnet continuously?
    Where is the sticky point that prevents from doing so?
  2. jcsd
  3. mfb

    Staff: Mentor

    To get a force on a magnet, you need an inhomogeneous magnetic field. Making a long, homogeneous field is pointless. A magnet (or anything ferromagnetic) will accelerate until it reaches the homogeneous region of maximum field strength, and everything beyond that is pointless.
  4. That device could give a one time shove on a magnet and so forth but you couldn't do continuous work with it, it needs switchable magnetic fields for that. The fields inside a 3 phase motor, for instance, is basically rotating around inside the stators which is why the motor can spin in the first place. It is MOVING magnetic fields that do work, not static fields. Just like static electricity, a voltage builds up if you rub a glass rod against a cat and you get a single spark. But the energy from that comes from the fact you moved the glass rod against the cat or fur piece or clothing, whatever, YOU are supplying the energy for that spark. The spark is gone, no more electrical work possible.

    Think of a surfer on the beach. The surfer moves through the water because of the moving wave. When the wave stops, the surfer stops, it's as simple as that. There has to be a moving magnetic wave to do work otherwise those fields are just like a smooth ocean, you get no free lunch there, if you want to move, you paddle your butt around on the surfboard, the ocean will do nothing to help you move till the next wave comes by.

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