h a l f b a k e r yMagical moments of mediocrity.
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Take an extraordinarily long track ,either
a
pipe or some sort of walled track a ball
bearing could roll easily through will little
drag, several hundred ball bearings, 1/2
or 3/4 inch, and a few hundred rare
earth
magnets. the idea is this, align the
magnets at calculated (i dont know
the
equations, but I'm sure they're out there)
intervals so that when the ball bearings
leave one side of the magnet, they are
immedately pulled to the next magnet.
lets try an illistration.
O=ball bearing II= magnet.
O_____IIOOOO______IIOOOO
__________IIOOOO
O>___IIOOOO______IIOOOO
__________IIOOOO
_____OIIOOO__O>__IIOOOO
__________IIOOOO
_____OIIOOO______OIIOOO
___O>____IIOOOO
_____OIIOOO______OIIOOO
_________OIIOOOO->
so the fisrt ball is rolled to the magnet,
accellerated into it, so the energy of that
colission is transfered through the first
three bearings of the other side of the
magnet and launches the 4th magnet,
which is the accelerated toward the next
magnet ect.
not sure if there is an upper bound to the
acceleration from the magnets or if this
would work, so anno away all comments
are welcome.
The video that I imagine bleh has seen.
http://www.metacafe...ch/20901/metal_gun/
[st3f, Sep 14 2006]
(?) Baked.
http://demo.physics...ipt.idc?DemoID=1098
They call it a Gauss rifle. [spidermother, Sep 14 2006]
[link]
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I'm not sure where the limit is, but I've seen it demonstrated and the science is sound. Is there a new idea here though? |
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(edit: that is, find a novel use for it, maybe drilling holes in tungsten plate or something, to justify the idea's existence. I for one like it) |
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Umm, as I understand it, the magnetic force operates on an inverse cube law, so it's effect never "ends," it just gets weaker and weaker. I'd imagine that if the ball bearings are accelerated at all, they'll be accelerated only to a particular magnet, or just maybe between two magnets. |
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I believe that most rail guns require electromagnets to be turned on and off at alternating times, or to reverse polarity, and the fluctuating magnetic field is what accelerates the ammo, so a passive rail gun, as you describe it seems to border on perpetual motion territory. |
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Of course, my science isn't exactly up to rocket-engineer level, so I'll refrain from boning until my hunch is verified. |
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[YRZ] has it right. Otherwise you have created a perpetual motion machine. |
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This is feasible, and will work. It won't be nearly as effective as the active rail gun for the reasons brought up by [ye_river-xiv]. |
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The problem you face is that since you can't turn the magnets off, you can't stop them interfering. So the magnet forces won't sum directly. It's certainly won't be perpetual motion, it's a poor rail gun. |
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Not true G_C; google for it and you'll find it. |
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What happens is that the first ball bearing is rolled into the magnet. Magnetic attraction pulls it in (it loses magnetic potential energy) and it transfers its kinetic energy through the magnet and the string of ball bearings, to the fourth ball in the diagram. This ball, being the last in the string, has nowhere to transfer the KE to and is also relatively far from the magnet, so it can escape the magnetic field and does so with a lot of KE. It heads for the next magnet, which accelerates it on the way in, and transfers all the KE it has (including that provided by the second magnet) through the next string of balls. Repeat until the last ball is going very fast. |
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That last ball has all of the magnetic potential energy lost by the balls which are now stuck to magnets, plus the little KE you gave it by rolling at the start. No perpetual motion. |
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[Jinbish], they'll more or less sum directly, because the KE is being passed to a ball that is relatively far from the magnet. The magnetic forces will cancel one another out, except for the period when the incoming ball is closer to the magnet than the outgoing ball (three diameters or so in the four-ball case). As the magnet follows a 1/x rule (I think? it's inverse, in any case) the force exerted while the incoming ball is within those three diameters is significant. |
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I see - like the office toy. In this case you rely on the transferral of KE being close to an elastic collision and the influence of the magnets being inverse square. So, assuming no friction (!) and elasticity, you should gain energy proportionally to :
f(no. magnets, diameter*no bearings) or something similar... |
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Ok, I guess I was not completly understanding what was going on. Calling it a "rail gun" is really confusing me. It looks vaguely like a sort of interrupted mass driver, or an overly complicated newton’s cradle. |
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But you still are not going to get any more energy out than you put in. If you drop the first ball in from a distance of two inches from the center of the magnet, the ball on the other end is going to pop out to a distance of two inches from that same center |
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Momentum seems to be conserved the
pack seems to recoil. |
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Energy seems to be conserved. The
ball bearing entering has a small
amount of kinetic energy and lots of
potental energy due to attraction from
the magnet. The ball bearing leaving is
further from the magnet and therefore
not going to be have to come out of
such a deep potential well. |
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Assuming all the ball bearings are the
same, the factors affecting a compund
weapon of this type would be the limits
of elastic collisions of the ballbearings
and the magnets. As soon as either
starts deforming during a collision
energy would be lost. Imagine
repeatedly dropping a ball bearing onto
a metal surface from increasing heights.
Imagine the impact speed that starts to
damage the ball bearing (or the magnet)
-- that's the
speed at which the efficiency of the
compound magnet gun would start
tailing off. |
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Finally, all this is under the assumption
that all the ball bearings are identical. If
I were building a toy like the one in the
linked video, the ballbearing that gets
fired would be very different to the rest.
It would be non-magnetic to reduce the
retarding force of the magnet on it and
it
would be much lighter to make the
momentum transfer more visible. These
changes would invalidate this toy's use
as a compound weapon. |
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Baked (link)."This is simply a wooden ruler with 4 super magnets taped along the length. Ball bearings are set between them so that the introduction of a new ball bearing at the start (top) causes a rifle-like chain reaction of force that pushes the red ball off at the end" |
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Theirs has only two ball bearings after each magnet, and, yes, the last one is non-magnetic. |
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All but the last ball bearings on the far side of each magnet should be nonmagnetic. Otherwise the magnetism will be transmitted along the line of ball bearings the the one which is supposed to move forward into the next magnet. It would be preferable if the others were carved out of petrified whale testicle. |
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//find a novel use for it//
maybe a defence system built into a tall
tower? suspend the whole thing
vertically so that gravitational potential
is added to the magnetic. im imagining
a fort with these built into the towers.
sevreal in each tower, so that it can
spray whatever chosen ammo out in all
(outward) directions. Given, it would
need to be a really tall tower, but might
work, if its shoting poison darts or
smoke bombs, someting relatively light. |
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[st3f]: hadnt seen the video, and still
cant since my players are outdated and
im lazy, but i saw a picture similar to
the one in [spidermother]'s link but only
a one stage. thanks
to both, i couldnt find again. the idea
was to chain a copious ammount of
these together, and space them so that
they have the same sort (maybe not
magnitude) of acceleration as an active
railgun. I'm not looking to achieve orbit
with one of these, just shoot someting a
fair distance with nearly no energy input
(except setup/reloading). |
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TANSTAAFL=There Ain't No Such Thing As A Free Lunch (or in your case, Launch). |
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Oh, and as a weapon, this is going to have a ridiculously long and complex reload cycle. Each ball bearing is going to have to be moved back to its starting position. Forget just one, and you have a misfire. |
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Considering the time it would take to set for each shot, I don't think using such a device would be practical in a serious offensive role. |
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Ah, sorry [G_C] you beat me to it. |
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//I don't think using such a device
would be practical in a serious offensive
role.// |
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I doubt it would work offensively also,
but defensively in a fort, maybe, im sure
it would be a lot less efficent and
complicated than existing systems, but
i think it would be more interesting.
also, depending on the strength of the
magnets and the ammount of bals you
could suspend from each, it may be
possible to fire several times before
reloading, then the incredibly long
cumbersome contraption could
theoretically be fired in reverse. |
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To phrase it differently: The magnets are attracting the stacks of bearings, which would balance best with an equal number on each side of the magnet. So the bearings are moving "downhill", magnetically speaking, as the gun fires. The stacks of bearing move closer to the equilibrium of equal numbers on both sides of each magnet. |
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That's where the power comes from, and where you could calculate how much energy is available. This is only good for one shot, (maybe another a lot weaker) so it isn't perpetual motion. Recocking will take energy, as the bearings will have to be lifted "uphill" away from the magnets. |
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[Later] This isn't an original idea. Fishbone. |
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The way this is described, it will effectively act like a magnetic "crossbow". Is it possible to actually get a higher projectile velocity with this than a system based on springs? Better novelty value, anyway. |
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I was thinking instead of having regular magnets what about electro magnets so then with the origanal idea- when the ammo goes down the track it gets pulled and then that magnet shuts off before
the ammo gets stuck to it and that just keeps happening, this is actually a gauss cannon/gun/whatever and not a rail/cannon/gun/whatever. but its still pretty cool |
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