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What material for weapons and tools would a tribal/medieval society use if there was a magnetic field preventing the use of iron? The iron would be attracted by the ground, obviously. It can`t be used for arrows for example as they would not get to far.

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    $\begingroup$ I don't really understand how a planetary magnetic field could 'prevent' the use of iron. What do you mean by prevent? Does it rust or explode or break or simply fade away? $\endgroup$ – kineticcrusher Dec 28 '18 at 16:21
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    $\begingroup$ Does this mean that no metals that are affected by magnets can be used? Can they even be used to make other alloys? Because not all iron based steels can be affected by magnets. $\endgroup$ – K Mo Dec 28 '18 at 16:28
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    $\begingroup$ @EdwardConstantin - There's a number of different magnetic materials, of which iron is probably the best known. I think a clarifying question would be "how strong is your planet's magnetic field?" and/or "how large an area does the magnetic field cover?". Note that magnetic fields fall off as the cube of the distance, so your field strength would be absolutely enormous - you might want to figure out at what point moving the object generates a noticeable electric charge. $\endgroup$ – Clockwork-Muse Dec 28 '18 at 18:18
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    $\begingroup$ keep in mind that way before the effects on iron weapons can be felt, humans would have a really bad time for being subjected to strong permanent magnetic fields. $\endgroup$ – brett Dec 29 '18 at 11:26
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    $\begingroup$ @Mazura check out the Adverse Events at the end of this article: fda.gov/Radiation-EmittingProducts/…. The thing is MRI is usually performed over a short timespan and there are [albeit rare] side effects. I imagine living long-term in such a field would affect even the less-sensitive people. Plus there's also iron in blood. Some effects would definitely have to be felt over time, if there were such a strong field that would affect iron tools/weapons. $\endgroup$ – brett Dec 29 '18 at 21:47
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Ceramic knifes would be cool:

A ceramic knife is a knife designed with a ceramic blade typically made from zirconium dioxide (ZrO2; also known as zirconia). These knife blades are usually produced through the dry-pressing and firing of powdered zirconia using solid-state sintering.

(Wikipedia)

I'm not sure if this technology is feasible for a medieval society - but its fiction, so why not?

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    $\begingroup$ Well, stone knives have been a thing for a couple years now. Chip away at a pot shard and you should have a reasonable "ceramic knife"! $\endgroup$ – elemtilas Dec 28 '18 at 17:02
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Earth's history is filled with non-magnetic weapons and tools. The Iron Age was named for the increasing use of iron in tools and weapons -- before that, bronze, copper, wood and stone did the same jobs, perhaps not quite as well, but well enough to do the job for many centuries.

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  • $\begingroup$ I don't know what you mean by "Christian Era", here, since iron had been worked for at least a millennium before the birth of Christ, and the iron age itself "ended" (see article) 500 years before then too. $\endgroup$ – Clockwork-Muse Dec 28 '18 at 18:09
  • $\begingroup$ @Clockwork-Muse Okay, thinking about it, I recall the "Bronze Age Crash" being around 1177 BCE, so I was off close to a thousand years. Edited. FWIW, iron working preceded the Iron Age by a bit -- meteoric iron, bog iron, etc. were workable with bronze working tools; the Iron Age was denoted by the ability to extract iron from ore and the near-complete replacement of bronze by iron. $\endgroup$ – Zeiss Ikon Dec 28 '18 at 18:43
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    $\begingroup$ If the magnetic field is strong enough to interfere with using iron weapons, it'll probably induce lethal electric currents in bronze and copper ones when you swing them around. $\endgroup$ – Mark Dec 29 '18 at 2:47
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I used to work for a company that makes 1.5 T and 4 T MRI machines. We used brass tools in and around the magnets.

They did some research into an open magnet design to be used in the operating room during surgeries. The surgeons would have used brass instruments, with ceramic scalpel tips. However, the concept never made it into product.

It should be noted that in a magnetic field, torques are a bigger hazard than linear forces. In other words, you are more likely to have a tool twist your wrist than get "sucked" into the magnet.

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  • $\begingroup$ That means a sword wont be fiable due to the fact that it will always be turned on the wider part and not on the edge. Am I right? $\endgroup$ – Edward Constantin Dec 28 '18 at 22:47
  • $\begingroup$ If it is ferromagnetic (iron, steel), there will be a torque to align it with the magnetic field. However, magnetic fields have no effect on non-magnetic materials (brass, wood, ceramic) and everything would be normal. It's likely that such a culture would skip the iron age and keep using brass and bronze for inventions and weapons. $\endgroup$ – DrSheldon Dec 28 '18 at 23:01
  • $\begingroup$ You are experienced in this domain. If an object has a big speed, lets say 44 m/s trough this field, will it obtain an electric charge (basically making it an electric sword?) $\endgroup$ – Edward Constantin Dec 28 '18 at 23:18
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    $\begingroup$ Theoretically, that will induce a voltage which separates the charges on an object, and is the basis of an electric generator. However, you need a complete circuit for the charge to go anywhere. Also, the voltage induced is far too small to hurt someone -- it's no more harmful than getting hit by a normal sword. $\endgroup$ – DrSheldon Dec 28 '18 at 23:30
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    $\begingroup$ The dielectric strength of air is way too large for that. $\endgroup$ – DrSheldon Dec 29 '18 at 0:27
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Stick with bronze.

You may have heard of the bronze age, a time in which all metal tools were made out of bronze (not iron or steel). Bronze is a non-magnetic metal alloy used in human history to make tools, and weapons, and pretty much anything you would make out of iron.

Bronze is a simple historically friendly answer to a substance that can easily be used in a strong magnetic field.

After the bronze age, a civilization might proceed directly to the plastics age if iron is not feasible.

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    $\begingroup$ Most non-sparking tools are made out of a bronze alloy; the high copper content prevents sparking. This is a good thing in refineries and petro-chemical plants. $\endgroup$ – Catalyst Dec 28 '18 at 19:21
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    $\begingroup$ Note that depending on the magnetic field any conductor and thus all metals could be useless as a weapon due to eddy currents, though the implications of such a magnetic field on society will most likely go far beyond the prevention of certain weapons. $\endgroup$ – Ezra Dec 28 '18 at 20:51
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Use whatever materials you want:

As you say:

The iron would be attracted by the ground

The thing is that arrows already are attracted to the ground - by gravity. You have to ask just how strong this magnetic field must be to noticeably deflect arrows.

Some experiments have been done on this with bullets including by the Mythbusters but they used non-ferrous ammunition.

The following video however shows an experiment with a powerful neodymium magnet and a steel ball from a low-powered air rifle. There is some deflection but they fire very close to the magnet and I don't suppose your landscape is made of neodymium. https://youtu.be/pXDLGNKoR2c?t=279

Firing near a the world's most powerful MRI machine that has a 45-ton magnet and generates a 9.4-Tesla magnetic field would definitely deflect or even stop an arrow but there's nowhere to plug one in during medieval times.

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  • $\begingroup$ The ground would be very magnetic, basically making every iron object much heavier. I think they could use some iron melee weapons in this case if they are very strong $\endgroup$ – Edward Constantin Dec 28 '18 at 17:02
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    $\begingroup$ Let's say arrows are 5 feet above the ground when fired, then nothing short of a multi-Tesla MRI machine will deflect them appreciably. Incidentally the Earths magnetic field is about 10 micro Teslas $\endgroup$ – chasly from UK Dec 28 '18 at 17:06
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Since there were many suggestions of non-magnetic metals: They aren't usable for many purposes, specially for fast moving parts: Eddy currents will slow down the motion.

So the culture should go for isolating materials: Wood, ceramics, and glass.

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