On Wednesday, May 20, 2015 at 2:37:19 PM UTC-4, wrote:
I've always wondered if it's possible to use a very powerful magnet to
remove nails from lumber? I'm sure that the magnet would have to be a
really strong electro-magnet, such as the ones they use to lift cars at
auto junkyards.

However, if this is possible, it may not be something that should be
exposed to the public, because it could become a weapon. In other words,
someone drives up to your home, activates the magnet, which removes all
the nails as well as steel plumbing, metal electrical boxes, your
appliances, and so on. This, in a matter of seconds, your home would be
nothing but a pile of lumber, with all your (non-iron) furnishings
buried in the pile, and all your iron metalic furnishings as well as all
the nails from your home, leaving the scene by some crook.....

And, dont forget, your belt buckle is metal. Say goodbye to your
pants!!!

Here's a source for an electromagnet that lifts 2,000 pounds:

http://www.adamsmagnetic.com/magneti...tromagnets.php

One thing to consider is that magnetic force, like gravity, decreases with the square of the distance, so an electromagnet weapon would have only limited range. Besides the electromagnet, you'd need a generator to power it.