Anime: Railgun

[TroyGuffey]

I've picked up a new anime "Railgun" about psi(mutant?) powered individuals. Young girls, naturally....

The top psi is an electro-controller nicknamed "Railgun" for her signature ability. She controls electric fields (static and flowing) around her body, and is able to fire off coins at 1024 m/s.

First, is this actually possible (using tech, of course) firing projectiles just through manipulation of electric fields?

Second, how should this be modeled in GURPS? (3e AND 4e)

[Purple Haze]

Every electric field has a magnetic field of equivalent strength perpendicular to it.

So if she can make electricity flow around her body, she must be able to make magnetism do the same.

[whswhs]

When I allowed creation of a character with a similar ability, I based it on his control of magnetic rather than electric fields; that's what real world designs for railguns use. Of course you can set up a moving electric field and generate a magnetic field, per James Clark Maxwell.

Doing it this way, you'd need projectiles made of ferrous metal.

In principle, you could repel small objects electrostatically, but you'd need an opposite charge somewhere, which might attract them. I suppose you could psionically put the opposite charge on your target! Electrostatic repulsion isn't all that powerful; I'd have to dig out Halliday and Resnick to check the equation.

Bill Stoddard

[whswhs]

Originally Posted by Purple Haze

Every electric field has a magnetic field of equivalent strength perpendicular to it.

Only every changing electric field. A static field has no magnetic effects.

Bill Stoddard

[Purple Haze]

Originally Posted by whswhs

Only every changing electric field. A static field has no magnetic effects.

Bill Stoddard

Hence the word "flow".

[Anthony]

There's a fair amount of bad physics in A Certain Scientific Railgun (for example, a coin at 1024 m/s is actually rather underwhelming), but it is certainly possible to accelerate metal objects with electromagnetic effects.

[vierasmarius]

Originally Posted by TroyGuffey

Second, how should this be modeled in GURPS? (3e AND 4e)

I can't answer much for 3rd edition, since I'm no longer using it and don't have the books handy. Might be possible with the Psionics rules, either with Electrokinesis or by adapting Telekinesis.

In 4e, there are a couple ways to handle it. The most literal is with Telekinesis limited to only apply to ferrous objects. You then use your TK strength to "throw" the object. That can get complicated rules-wise though, so I'd recommend building the "throw" as a separate Innate Attack, an Alternative Ability to the Telekinesis. For more details on building these sorts of powers, and a plethora of ready-made examples, I'd recommend picking up Psionic Powers. The Powers book itself would also be helpful.

[roguebfl]

Originally Posted by Anthony

There's a fair amount of bad physics in A Certain Scientific Railgun (for example, a coin at 1024 m/s is actually rather underwhelming),

why? bullets 400–475 m/s, with a bullet weight of ~16–22 grams

of course the heaviest Japanese coin is 500yen Nickel-brass Coin

Material : Cu72%, Zn20%, Ni8%
Diameter : 26.5mm Weight : 7.0g
Edge : Milled
Year of First Issue : 2000

the lightest 1yen Aluminum Coin

Material: Al100%
Diameter: 20.0mm Weight: 1.0g
Edge: Smooth
Year of First Issue: 1955

however speed has a bigger impact the mass.

[whswhs]

Originally Posted by roguebfl

why? bullets 400–475 m/s, with a bullet weight of ~16–22 grams

of course the heaviest Japanese coin is 500yen Nickel-brass Coin

Material : Cu72%, Zn20%, Ni8%
Diameter : 26.5mm Weight : 7.0g
Edge : Milled
Year of First Issue : 2000

however speed has a bigger impact the mass.

For a bullet, you're looking at a minimum of 6.4 kg-m/sec linear momentum, and 1.28 kJ kinetic energy. For the heaviest coin, you're looking at 7.2 kg-m/sec linear momentum, and 3.6 kJ kinetic energy. But I suspect the drag force is going to slow it down and cost you range.

Bill Stoddard

[roguebfl]

also note Iron (Fe), Nickel (Ni), Cobalt (Co), and Gadolinium (Gd) are all ferromagnets.

so nickle in the coins doe give railguns something to work with, but it is inferior to iron for that purpose so takes stronger fields.