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Suppose I have a magnet and I put a piece of iron next to it, then the magnet will attract it.

Now if I put a piece of wood in front of the magnet and the piece of iron, the iron will not get attracted. Why?

Now I have heard that gravitation is also magnetism, so it should also show the properties similar to that of magnet but it is not so, even if I put a big building between ground and the object it gets attracted. Why?

ACuriousMind
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user5954246
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  • What? I'm pretty sure most wood does not significantly block magnetic fields (there are even wooden toy blocks with magnets inside!). Also, gravitation is not magnetism. At all. – ACuriousMind Feb 27 '16 at 18:07
  • Gravitation, unlike electromagnetism, is not a force. In Newtonian physics gravitation is an acceleration and in general relativity it is a distortion of spacetime. Unlike electromagnetism gravity doesn't require the existence of charges inside the objects that are subject to it. Electric fields can only attract (or repel) objects that carry an electric charge (or dipole moment) and magnetic fields can only exert forces on objects with electric currents or magnetic dipoles in them. That's why there can be non-magnetic objects. Gravity doesn't require any such charges, so one can't prevent it. – CuriousOne Feb 27 '16 at 18:37
  • Possible duplicates: http://physics.stackexchange.com/q/2767/2451 , http://physics.stackexchange.com/q/19896/2451 and links therein. – Qmechanic Feb 27 '16 at 18:56
  • Some magnets have very weak fields which become inconsequential at a few millimeters. Unless the wood is very thin (~1 mm) you won't notice any attraction. – Bill N Feb 29 '16 at 23:00

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There are a couple mistaken assumptions in your questions, which render your questions meaningless.

First, wood has almost no effect on a steady magnetic field. The relative permeability of wood is $1.00000043$, which for most purposes is negligibly different from the relative permeability of air ($1.00000037$) or vacuum ($1$).

Second, saying that "gravitation is also magnetism" isn't really true. Kaluza-Klein theory provides a unification of gravitation and electromagnetism into one theory, but that doesn't mean that gravitation and electromagnetism are the same thing any more than the electromagnetic force and the strong force can be said to be the "same thing" because quantum field theory provides a model which encompasses them both. Gravitoelectromagnetism also points out similarities between gravity and electromagnetism, but gravitoelectromagnetism is only an analogy that's only approximately valid under a limited set of circumstances. Gravitation and magetism are different phenomena.

Red Act
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