Is it possible to stop a bullet by just using a magnet?

[Omar Ibrahim]

Stop it or deflect it? and what are the laws and the effects that I need to know to determine something like this?

 

[.Scott]

Stopping it would definitely be a technological fete. But, in principle you could do that.
Although lead is not considered a magnetic material, it can be moved by a magnetic field.

To give you a sense of what might be required: Set the experiment up in orbit. This eliminates the problem of having to actually hold the bullet up against gravity when the bullet stops. The vacuum will also make it clear that only the magnetic field is responsible for changes in the bullets velocity. Then fire the bullet through a tube that will match the bullet's trajectory. All along the tube would be powerful electromagnets that would be activated as the bullet passed by - to slow the bullet and keep it in from striking the sides of the tube.

If the bullet has a brass jacket, the effect from the magnets will be better. Here are links to pages with videos showing the effect of magnets on lead and brass.:
https://terpconnect.umd.edu/~wbreslyn/magnets/is-lead-magnetic.html
https://terpconnect.umd.edu/~wbreslyn/magnets/is-brass-magnetic.html

 

[anorlunda]

I like @.Scott 's scenario. But in space, there is no minimum relative velocity for a bullet. So it is trivially easy to stop something moving arbitrarily slow. I could just hold the magnet and let the bullet hit it. Come to think of it, a big heavy magnet can stop a fast bullet if you use the magnet for the target.

OP, you need more effort to properly phrase your question here on PF.

 

[Khashishi]

If you fire a metal bullet through a bunch of magnetic coils, eddy current braking should slow down the bullet some, and there will also be a reaction force on the magnets, so they need to be rather robust. But, since bullets are small (which reduces the size of the eddy currents) and very fast, I'm not sure it will be enough.

 

[rumborak]

Mythbusters has an episode on that topic, where they try to deflect a bullet with a magnet. The best they manage is by lining up a rail of super strong permanent magnets and then shoot the bullet a millimeter above the rail along it. The deflection they get is still tiny and it grazes the last magnet.

 

[davenn]

Mythbusters has an episode on that topic, where they try to deflect a bullet with a magnet. The best they manage is by lining up a rail of super strong permanent magnets and then shoot the bullet a millimeter above the rail along it. The deflection they get is still tiny and it grazes the last magnet.

I remember that episode
If you hadn't mentioned it, I was going to

 

[thejosh]

Well, you would have to have an insanely powerful magnet or otherwise increase the duration of the bullet in the magnetic field such that over time the force would eventually overcome the bullets momentum, such a magnet probably does not exist at the moment and since you need a stronger magnet to increase the force field range or in the case of the myth busters more magnets in the path of the bullet I suggest you take this up with science fiction until technology advances a little more.

 

[Nidum]

Mythbusters has an episode on that topic, where they try to deflect a bullet with a magnet. The best they manage is by lining up a rail of super strong permanent magnets and then shoot the bullet a millimeter above the rail along it. The deflection they get is still tiny and it grazes the last magnet.

The deflection was just as likely to have been caused by aerodynamic effects .

 

[Omar Ibrahim]

Thant you guys, I was working on scientific research about it but I need to take it to science fiction till technology advances

 

[Omar Ibrahim]

Stopping it would definitely be a technological fete. But, in principle you could do that.
Although lead is not considered a magnetic material, it can be moved by a magnetic field.

To give you a sense of what might be required: Set the experiment up in orbit. This eliminates the problem of having to actually hold the bullet up against gravity when the bullet stops. The vacuum will also make it clear that only the magnetic field is responsible for changes in the bullets velocity. Then fire the bullet through a tube that will match the bullet's trajectory. All along the tube would be powerful electromagnets that would be activated as the bullet passed by - to slow the bullet and keep it in from striking the sides of the tube.

If the bullet has a brass jacket, the effect from the magnets will be better. Here are links to pages with videos showing the effect of magnets on lead and brass.:
https://terpconnect.umd.edu/~wbreslyn/magnets/is-lead-magnetic.html
https://terpconnect.umd.edu/~wbreslyn/magnets/is-brass-magnetic.html

what about lenz law ?

 

[rumborak]

The deflection was just as likely to have been caused by aerodynamic effects .

I disagree. If bullets were that susceptible to air fluctuations you couldn't use them for anything.

 

[.Scott]

what about lenz law ?

Lenz Law explains why it is possible to stop a non=magnetic, but electrically conductive bullet with a magnetic field.
As everyone agrees, the issue here is one of technology.
Also, if you don't put this thing is a zero-G environment, the magnetic field will only be able to stop the bullet's horizontal velocity. Attempting to stop its fall due to gravity would involve large eddy currents - likely strong enough to quickly melt the bullet.

 

[.Scott]

Mythbusters has an episode on that topic, where they try to deflect a bullet with a magnet. The best they manage is by lining up a rail of super strong permanent magnets and then shoot the bullet a millimeter above the rail along it. The deflection they get is still tiny and it grazes the last magnet.

In this Mythbuster segment, they rated a James Bond magnetic deflection device as "Busted":
http://www.discovery.com/tv-shows/mythbusters/mythbusters-database/electromagnetic-deflect-bullet/

I couldn't find one involving a rail.

 

[Zachary Burell]

Josh you could have the strongest magnet in the universe but magnetic forces do no work thus they can't change an objects kinetic energy,

 

[thejosh]

Unfortunately Zachary I strongly disagree as I believe that is not a correct analysis as magnets can do work its just gravity that does no work when an object is at a certain distance to the larger body but since a magnetic field is able to pull a body towards it as work is defined as force * distance in the direction of the force a magnet is by definition is able to do work just check out this site https://van.physics.illinois.edu/qa/listing.php?id=17176 .And on top of that kinetic potential energy is defined as 1/2 mv^2 because this formula includes velocity which is a vector quantity anything that changes the direction of an object and/or the motion therefore changes its kinetic energy. . But my point was that the force needed to stop abullet using a magnet is not achievable right now.

 

[mfb]

Magnets don't do work on electric charges. This thread is not considering electric charges, and to deflect something you don't have to change the speed of the object.

A very rough estimate:
Let's be optimistic and make the bullet itself a strong magnet. 1 cm³, 1 T, 7g. It moves towards a target at 300 m/s, quite slow. Ignore aerodynamics. How can we deflect it? It won't feel a force in a homogeneous field, we need an inhomogeneous field. The best quadrupole magnets in the LHC can provide a peak field gradient of about 200 T/m over a few centimeters. This leads to a force of 160 N. If we can let the bullet travel along 1 meter of these magnets, we get this force for 3.3 milliseconds, for a final vertical velocity of 75 m/s and a deflection of 13 cm.
That might be enough to make a bullet miss a head, for example. But it means the bullet has to hit the central spot of a meter-long tube with a deviation of not more than 2-3 centimeters. If we know the bullet will hit exactly there, it is much easier to just move the head out of the way.

If you surround you with a big coil, 10 T/m over a meter is a more realistic (but still optimistic) field gradient, and then you get a deflection of less than a centimeter - towards the coil. On the positive side, this big coil will stop the bullet mechanically, and you don't even have to power it for the mechanical shielding effect...

 

[Nidum]

I disagree. If bullets were that susceptible to air fluctuations you couldn't use them for anything.

A projectile skimming very close to a surface certainly can be deflected by aerodynamic effects . Trying to work out which way it will be deflected is the hard part .

 

[Vanadium 50]

On the positive side, this big coil will stop the bullet mechanically, and you don't even have to power it for the mechanical shielding effect...

This is getting close to "I'll give you this swell magnet if you promise not to shoot me."

 

[Zachary Burell]

Josh you could have the strongest magnet in the universe but magnetic forces do no work thus they can't change an objects kinetic energy,

I always forget that this is applicable to charges. and that magnetic torque on a current carrying loop can do work, now whether this applies to bullets...doesnt seem very likely that one could consider a general bullet to have any amount on non-neglible circulating current...however if one were induced...then bullets would start being made from non conducting materials...and would circumvent any electromagnetic countermeasures

 

[Zachary Burell]

I always forget that this is applicable to charges. and that magnetic torque on a current carrying loop can do work, now whether this applies to bullets...doesnt seem very likely that one could consider a general bullet to have any amount on non-neglible circulating current...however if one were induced...then bullets would start being made from non conducting materials...and would circumvent any electromagnetic countermeasures

also a non-uniform B field will exert a force on any dipole moment , doing non-zero work

 

[Dr. Courtney]

The figure below shows the force stopping a 9mm bullet as it penetrates ballistic gelatin. The stopping distance is about 30 cm. The peak force is about 10,000 N. Of course, the force is greatest right after the bullet impacts and begins to penetrate. Impact energy is close to 600 J.

I like to simplify the physics of stopping bullets into work using the work energy theorem. The average force (in N) times the stopping distance (in m) needs to equal the initial energy of the bullet. If the initial energy is 600 J (typical of pistol bullets) and you can exert a force of 10 N, you need to exert the force for a distance of 60 m to stop the bullet. Exerting a magnetic force over 60 m is hard. Exerting a magnetic force of 10 N on a non-magnetic bullet (copper jacketed lead) is hard. Increasing the force to 600 N to reduce the stopping distance to 1 m is hard. Increasing the distance to 600 m to reduce the force to 1 N is hard.

 

[thejosh]

Its ok that's why we are here to learn, right? And that's why science is so interesting because we never stop learning and improving our understanding of it and it continuously grows and surprises us.

 

[The Wizard]

As Anorlunda stated, you could use a Magnet to stop the bullet, assuming it is strong enough not to break when the bullet hits it, which would be independant of the Bullet's material.

However, bullets come in a variety of materials, some of which would not be influenced by a magnet, for example a bullet made of plastic or rubber or even copper, so the clear answer to your question is No.

The only other way I can think of to stop a bullet using a magnet would be to insert the magnet into the barrel of the gun, that would probably stop the bullet.

 

[Physics_Kid]

short answer is yes, magnets can stop a bullet. how you do it needs engineering, physics, and a transfer 180 degree vector force equal or greater than the KE of the bullet. with losses, you'll need a ton more input energy to get the net transfer needed.

 

[Lowedown]

Yes you can deflect a bullet with a magnet but only if you set the magnet in the path of the bullet and let the bullet strike the magnet.

 

[Physics_Kid]

Yes you can deflect a bullet with a magnet but only if you set the magnet in the path of the bullet and let the bullet strike the magnet.

a super magnetic flux is all that is needed. look at how a disk drive needle works, just scale that up. there will be obvious constraints, but can still be done. and we are talking about electro-magnet, yes?

 

[mfb]

These constraints have been discussed in previous posts already.

 

[Physics_Kid]

super conducting electro magnets can rip you belt buckle off your waist!

magnetic impulse devices are interesting to this problem.

i am not sue OP asked for the engineering of the "how" question. i think with today's available resources is can be done. can it fit in a van, likely not.
perhaps fired in a vacuum tube where the mag flux (in small area) is on the order of stuff you see in far away places in the universe ??

 

[Nidum]

A draughtsman with a wry sense of humour working in No.8 DO once made the comment that if you wanted to stop a speeding bullet all you needed to do was fly along side in a Concorde , reach out of the window , pick the bullet up and put it in your pocket .

 

[Physics_Kid]

An draughtsman with a wry sense of humour working in No.8 DO once made the comment that if you wanted to stop a bullet all you needed to do was fly along side in a Concorde , reach out of the window , pick the bullet up and put it in your pocket .

hah, so in essence, all one needs to do is swing arm very fast and nab the bullet in flight ;)

i forget what show it was, years back now, a science show on tv, the lab builds these crazy high density electro-magnet using a lot of very thin current carrying stacked layers to create the coil (thus, coil density is extremely high). if i recall correctly, the frame was square or polygon shaped and the stack was ~4ft tall and. the darn thing could rip relatively heavy metal objects from across the room.

can it be done with an electro-magnet from ~100ft away, yep, but you need a lot of input energy and possibly some crazy laser light focusing of magnetic flux.

remember, 5w of Rf input to a omni antenna is very different than that same 5w of input power to a yagi. hence why the FCC typically doesn't regulate input power, they regulate spatial Rf power (density). the gross example is a very good high power laser, off to the side the laser is not a danger, get in its' path and you have a hole through your arm.

focus sunlight energy to a point an you get a ut-o.

 

[jbriggs444]

hah, so in essence, all one needs to do is swing arm very fast and nab the bullet in flight ;)

It's actually easier than that. Just adopt a frame of reference in which the bullet is already at rest.

There's probably a joke in there somewhere. A lawyer, an engineer and a mathematician are blindfolded in front of a firing squad...

 

[Physics_Kid]

It's actually easier than that. Just adopt a frame of reference in which the bullet is already at rest.

There's probably a joke in there somewhere. A lawyer, an engineer and a mathematician are blindfolded in front of a firing squad...

what 'for' would that be?

 

[jbriggs444]

what 'for' would that be?

In what frame of reference is the bullet at rest? The rest frame of the bullet, of course. Not sure what you are trying to ask.

 

[Quandry]

A very simple example can address this question. Electromagnetic dampening is used in balance scales, such as those used for measuring powder charges for 'bullets'.
The balance arm has an aluminium or copper extension which moves within a magnetic field. The effect of this is to dampen the balance arm swing so that it comes to rest faster illustrating that energy is lost from the balance arm as the non magnetic material moves through the magnetic field.

 

[Dr Wu]

The magnetosphere of a neutron star would do a pretty good job at stopping a bullet.