Attraction force of a small and large area?

  1. Hello!

    There is an interesting effect that I've discovered in magnets while studying E&M and experimenting.
    If the surface area where the magnet will be attracted to,for example the surface area of the steel plate is x4 times larger than the magnet, then there would be a stronger attraction force, it would take a lot of effort to pull the magnet off. However, this does not happen to a small steel nail x4 times smaller than the magnet.

    Nothing but the "area" has changed in both cases however, the magnet is the same in both.

    What is the proper explanation of this?
    I contacted the manufacture of my magnets, they said it's true because of the area being x4 times larger and thicker than the magnet itself that would cause the whole magnetic field of the magnet to be "held". Is this right? What do you all think of this?

    I think they have it posted on their website, I'll try to get the link soon.
    Last edited: Apr 14, 2013
  2. jcsd
  3. Simon Bridge

    Simon Bridge 15,474
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    Well done - I'm a big fan of people discovering physics through experiments.

    Think of it this way - magnets attract iron.
    Therefore it would be sensible to expect that the strength of the attraction should depend on both the distance to the magnet and amount of iron present (maybe some other stuff too).

    When you keep the amount of iron the same, but increase the surface area facing the magnet, you are bringing more of the iron closer to the magnet. So you'd expect that the bigger facing area has the bigger attraction.

    When you changed the nail for the steel plate in your experiments, the surface area was not the only thing to change: you also changed the amount of iron you used. Therefore, you need to repeat the experiment, keeping tighter control of your variables ;)

    If you already have one iron plate in contact with the magnet - how does that affect the strength of attraction to a second steel plate? A third plate? etc. You may also want to investigate how changing the angle of the pull affects how easy it is to pull the iron and magnet apart.
  4. Well thank you Simon!
    Experimentation is a wonderful thing to do and the best way for me personally to lean Physics!
    Indeed! When increasing the amount of iron, there will be a greater force generated.
    My conclusion of the matter is, when most "manufactures" site the "Pull Force" of a magnet(i.e the maximum force a magnet can apply to attract or repel) they should remind us that, that force is achieved with a surface area 2+ times larger than than the magnet itself.

    I thought that when my Neodymium magnet (rated at 2.03lb of pull force) attracts "magnetic" object it constantly applies that amount of force. But I was wrong!
    Thankfully I learned this sooner than later... Phew!
  5. NOTE: Increasing the surface area would allow the magnet to apply its full force, there is a certain number where that is achieved.
    Constantly increasing the surface area after that point would not increase or decrease the force.
  6. Ow, I aslo think that the surface area of the magnet is also important to determine the force! But can't explain it...
    I remember once having a small magnet with a surface field of 5154 Gauss with a pull force of 1.3lb
    and compared it with another larger magnet with a surface field of 1795 Gauss with a pull force of 270lb.

    I still can't figure out the reason as to why the lager magnet would have a weaker field yet have a stronger force. Maybe its because it has more magnetized material thus having a lager surface area thus having a capability to generate a stronger force maybe?
  7. Any interests or comments :) ?
  8. Simon Bridge

    Simon Bridge 15,474
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    Same comments as before - remember - the magnetic field falls off with distance.
    You need to experiment to quantify the effect.
  9. Of course! How could I forget?!

    The distance is one of the most important thing to witness this effect.
    I'll continue hopefully to experiment more and discover more.

  10. Simon Bridge

    Simon Bridge 15,474
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    A proper study of magnetism in more involved - there are a lot of resources online, but to get beyond the basic "how stuff works" type you'll have to look for the college courses. The simple qualitative model above should serve for just what stick to what. Have fun.
  11. Well, I tend to read from college notes and watch some courses.
  12. Simon Bridge

    Simon Bridge 15,474
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    No worries then :)
  13. However, so far I have not found any explanation about the things I discovered from my experiments.
    I do understand a few things about magnetism and from it, I tend to answer my own questions.
  14. Simon Bridge

    Simon Bridge 15,474
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    You'll have to go carefully through the magnetism courses at college level.
    Most of what you have seen is just from the magnetic field spreading out in space... all the courses show you that surely? The rest is getting used to thinking about what they mean without getting distracted.
    You could see if you can find an engineering course on practical magnetism - that could be more direct.
    Certainly a detailed explanation is beyond the scope of these forums.
  15. But after learning the basics and all the main theories what would I gain if I go in depth?
    By knowing the basics I could figure out most problems and set-ups.
  16. Simon Bridge

    Simon Bridge 15,474
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    So... no worries then.
  17. Simon! I wanted you to know...

    I felt a bit guilty after saying this! I felt "un-scienetific"...(I.E not thriving for more knowledge!)
    But I'd like to point out that I've read a lot since!

    Watched many lectures that gave me a lot of insight.
    But thankfully, it supports my point. After learning the basic theories you can move on from there. And the "un-usual" cases I doubt to face, if I did... I'll be coming here to share it! Or try to figure it out.
    The best thing is... linking my experimental discovery to those theories! It feel so euphoric!! :)
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