Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

If e-magnetism is billions of times stronger than gravity then why a small magnet is

  1. Aug 30, 2008 #1
    not able to pick up a 1 kg iron object off the ground by overcoming the gravitational force between earth and the object.

    Consider this : It can pick up a 1 gram (iron) object easily. Then, the increase (from 1gm to 1 kg) would be by a 1000 times. Clearly that increase cannot account for the factorial difference of billions of times between electromagnetism and gravity. What gives?

    I know, I am making a simple mistake in my thinking somewhere but can't really figure it out.
     
  2. jcsd
  3. Aug 30, 2008 #2

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Re: If e-magnetism is billions of times stronger than gravity then why a small magnet

    You are misinterpreting the comparison. You can't compare bulk material, because a number of factors can affect the strength of the magnetic field (such as the purity of the material, and the temperature).

    What you CAN do is compare the magnetic "force" between two electrons, and then compare the gravitational strength between them at the identical distance.

    Zz.
     
  4. Aug 30, 2008 #3

    Dale

    Staff: Mentor

    Re: If e-magnetism is billions of times stronger than gravity then why a small magnet

    Without realizing it you are mixing a bunch of different topics. First, Newtonian gravity and Coulomb's law are both inverse square laws, but an ideal magnet is a dipole which does not follow an inverse square law. Second, the difference in the mass of the earth and the mass of your chunks of iron is much more than a factor of "billions". Third, you are comparing magnetism at a distance of a few inches to gravity at a distance of thousands of kilometers (assuming an ideal spherical earth).

    The first point is probably the most important for your practical experiment. If you placed your 1 gram object at the same distance from the magnet as the far side of your 1 kg object it probably would not lift even the 1 gram object.
     
    Last edited: Aug 30, 2008
  5. Aug 30, 2008 #4

    atyy

    User Avatar
    Science Advisor

    Re: If e-magnetism is billions of times stronger than gravity then why a small magnet

    http://www.youtube.com/watch?v=lmSyJSSuFpM&feature=related
    http://www.youtube.com/watch?v=kHXpZpcMLTA&feature=related

    To expand a bit on DaleSpam's and Zz's posts, consider the analogy of picking up a small piece of neutral paper with a charged comb. The charged comb induces a tiny polarization on the neutral paper that allows you to pick it up. You won't be able to pick up a stack of papers because the tiny polarization remains the same.

    A key thing is that the piece of paper itself is neutral, and the comb only induces the charge. It is different for objects with net charge. If a comb can pick up a small object with 1 net charge, it can pick up an object 1000 as big with 1000 net charges. For electromagnetism, there are positive and negative charges which cancel each other out to a very high precision (a tiny grain of salt is neutral, even though it has gazillions of charges). For gravity, there is no opposite charge, and so even though it is weak, it builds up over large distance. The neutrality of matter is why even though the electromagnetic force is much stronger than gravity, it tends not to be apparent at large distances.
     
  6. Aug 31, 2008 #5
    Re: If e-magnetism is billions of times stronger than gravity then why a small magnet

    Thanx guys, I think I am getting it. But, if anyone wants to add something, it'd be great.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: If e-magnetism is billions of times stronger than gravity then why a small magnet is
Loading...