How close does a magnet have to be to a metal object in order to have an effect on it?
84144
You need to define "effect".  It also depends on the strength of the magnet, but if you're talking about something like a fridge magnet or something like that it's a very small fraction of an inch before the effect is negligible.
105221
Well, the easiest way is to get some wire, wrap it around a iron/steel rod, and apply a current to the wire.\n\nTo get an electromagnet to have a lifting capacity that you specified, it will require a little more engineering work.  Trying to stay in the most basic terms, the power of your magnet will depend on how much current you put through the wire, how many turns you have around the iron rod, and something called the magnetic permeability of the iron rod.  Now there's some trade-offs with all of these factors.  More turns increases the magnet flux (strength), but requires more wire and increases the resistance.  More resistance means that you will need more current to counteract this problem.  Treating your electromagnet strictly as a resistor (which it is not), by following Ohm's law, you increase the current by increasing the voltage.   Too much current and you may end up melting your wire.   You want to keep the wire as small as possible so that you can get the turns as close as possible to your iron rod, but smaller wire has a higher resistance and lower current carrying capability.\n\nIt's a matter of balancing a lot of equations to get the best combination.  Your best bet is a little trial and error.
531203
prooly need ifrared thingy\ntry a industrial magnet
1018515
Any two magnetic fields will interact with each other. The same happens with the Earth's magnetic field and a magnet, although the Earths magnetic field density is very weak in comparison to a magnet. \nThe magnet will locally distort the Earths magnetic field, which can be seen by looking at a compass in just the Earth's magnetic field, then looking at the compass when a magnet is brought near.
969954
I think that metal detectors just work by setting up a magnetic field. When the apparatus move over a location that has a magnetic material a flux is produced that induces an electric current in the metal detector, activating a sensor.\n\nIf this is the case (i'm 95% sure it is), then the only factors affecting it's quaility would be within the machine itself as far the smallest current that activates the sensor.\n\nHeat and moisture would not change the magnetic field (moisture might theoretically alter the detectors magnetic field a little bit, but certainly not enough to measure). The both give the same result.
56297
elements fall under one of three categories: stuff that is always attracted to a magnetic field, stuff that is always repelled by a magnetic field, and stuff that can be magnetized ei you can make a magnet out of it. For example, water (yes i know its not an element) is always repelled by a magnetic feild, titanium is always attracted and iron can be magnetized. To see the effects of water being repelled by a magnetic field, buy some neodymium magnets, (the bigget the better) and place it in a bowl of water so that the magnet is barely covered with water. place it in front of your compurer screen, and look at the reflection of the computer screen in the water just above the magnet. you will notice th reflection is warped just above the magnet.
54860
When talking about a magnet large enough to be handled (and broken), it can be thought of as a collection of smaller magnets.  These smaller magnets are all aligned from north to south poles on each end.  If you got two 1" x 1/2" magnets, and put them end to end, N to S, they would make a magnet double the length of the original, and the ends would attract.  If you take the now 2" magnet apart, you have two magnets.  In practice, this is exactly what happened when you broke the magnet.  The pieces are still magnetic, with a north and south pole.  Therefore if you take the 2 pieces and put north to north or south to south, they will repel, and vice versa if north to south, they will attract.  No one yet has found just a south pole, or just a north pole, and that causes a stir in the scientific community.  You can keep crushing the magnet to bits and the tiny fragments will still have a north and south pole, and act like tiny little bar magnets.
41444
There are some natural magnets. For example, the mineral magnetite is magnetic, and is found in lodestones. \n\nIf you have a magnet, you can stroke a piece of metal (not all metals, but some) and magnetize it; that is, turn it into a magnet. You line up the magnetic domains when you stroke it so it has a net magnetic field. If you put a radio reciever nearby tuned to the right frequency, you can hear the domains flip as you do this; this is called the Barkhausen effect. \n\nThere are also electromagnets. Passing an electric current through a coiled wire wrapped around the right kind of metal (called a shunt) produces a magnet. This is the kind of magnet one finds in MRI machines.
1045884
http://en.wikipedia.org/wiki/Magnets\n\ngo there if u wanna find out, i only know simple version...
605330
well, if an object is moving, there must be some physical force applied to it - magnetic field, static electicity, pull from a sting, air pressure from a fan.
1001462
Magnets have no effect on your body whatsoever.  But feel free to fool yourself into thinking they'll do something anyway.  Science doesn't have the answers, turn to pseudoscience.
927615
Actually paper does interact with magnetic fields.  It "hinders" the magnetic field.  I am referring to the ease with which the magnetic flux can pass through a substance.  Everything has a such a value.  It is comparable to the dielectric constant in capacitors.  Metals pass magnetic fields fairly readily though there is some difference even between the metals.
1008527
It only can be a magnet when it the metal  can be a magnet.\nKeep it near a magnet. (The metal of a loudspeaker)
886336
Different metals have different magnetic field strengths.\n\nFor example, neodymium magnets are among the strongest.
91676
I answered your question already.  Magnetic field strength is governed by amount of current flow.
1180717
It truly depends on the amount of Iron in the magnet as to the strength and the base material that it is made of.  Some of those cheap rubbery refrigerator magnets will deteriorate or dry rot over a period of years and thus lose it's quality.  \n\nHow ever a good solid high iron ore magnet will easily out live you.  (with proper care)
1053942
depends on the type of metal