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  • magnets

    i just found out that a neodyme magnet will stick to a kitchen type magnet much less than to steel. also there is no repulsion when you turn it around. i also see that the kitchen magnet only adheres to steel with one side (once you remove the plastic). i also have "regular" magnets, that stick to steel with both sides and there is repulsion with the neodyme magnets.

    why is that? are magnets not just magnets?

  • #2
    You could get hurt if you fingers get between two good Neodymium magnets.

    A friend of mine deigned some light weight power generation equipment for the military that used them. He never got his fingers between the magnets, but he was working overtime for stock options in an non publicly traded company and got burned.

    My favorite Neodymium trick, I was shown this 15 years ago:
    Get a big neodymium magnet and put it next to your ear.
    Drop a dime [Copper] on it.
    It does not make a sound, due to eddy current counter EMF.
    There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. -Ernest Hemingway
    The man who makes no mistakes does not usually make anything.-- Edward John Phelps

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    • #3
      Ferrous material can be magnetized with the poles in various places, not just on the opposite ends. Considering it's purpose, I'd expect the kitchen magnet has both poles on one side with a space between them. A test with some iron filings might show this is the case.

      Since the flexible kitchen magnet has ferrous material in a matrix of rubber, the attraction of the stronger magnet is less than it would be for solid steel.

      The neodyme magnet is so much stronger than the kitchen magnet that it overpowers it regardless of how the poles are arranged.
      Any products mentioned in my posts have been endorsed by their manufacturer.

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      • #4
        The refrigerator magnets are actually made up of small particles of ferrite bonded in a nitrile rubber matrix. The particles can be magnetized in any direction. Typically, for the best attraction for a ferrous surface, the particles are magnetized in long narrow parallel strips of alternating North and South poles with an internal u-shaped return field between the poles. If you rub the faces of two bonded nitrile magnets together in the right direction you will feel the "cogging" between the magnets as the poles slide past each other.

        Now for the Neodymium magnet: The strength of these magnets are such that they can force the fields of the weaker ferrite magnets to saturate and rearrange. As an example, if you rub the North pole, say, of a Neodymium magnet all over the surface of the refrigerator magnet you will find that the refrigerator magnet may not be as strong as it originally was. You have rearranged the field so that only one pole is against the steel refrigerator and the opposite pole has to take a longer path out through the air to complete the return path for the magnetic circuit.

        I demonstrated this phenomenon to useful purpose in the Summer 2008 issue of Digital Machinist by selectively "reprogramming" refrigerator magnet material to build a rotary encoder. Also, in the Fall 2008 issue of DM, I carried it a bit further by "programming" a long belt of bonded nitrile magnet with musical note patterns, to be "played back" with a series of Hall sensors, much like a player piano. In the next article I used the output of the Hall sensors to drive a solenoid-operated glockenspiel.
        Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
        ~Practitioner of the Electromechanical Arts~

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        • #5
          Steel can conduct a lot more magnetic field lines that the 'fridge magnet can. Hence the strong magnet will attract less strongly to the 'fridge magnet. Put another way, to a very strong magnet, the 'fridge magnet is only 'partially there'.

          An interesting experiment, for me at least, was to see what interaction could be had between a super magnet and a speaker ring magnet. The super magnet could easily create a 'dead' spot on the ring magnet. I'm sure it could also enhance the strength of the magnetic field if you built a magnetic field path around the two magnets.
          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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          • #6
            Straighten a 3/8"x three or four feet copper tube as best you can.
            Get some neodymium magnets smaller than the tubing so they will free fall through it.

            Hold the top by your ear with the bottom on the floor,drop the magnet through the tube and listen.

            You expect to hear"sliiiide,click". Not the case at all.

            I progressively stacked more magnets together. At five magnets it took six seconds for them to free fall 40"

            At six, the weight overcome the EMF and they started picking up speed again.

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            • #7
              so how exactly does the magnet interact with the copper?

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              • #8
                The moving magnetic field induces current in the copper.

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                • #9
                  And the induced field interacts with the magnet, thus slowing it down.
                  I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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