Pushing/Pulling a moving object

[DeadFencer]

So we know Pushing and Pulling have clear rules. Anything more massive than you pushes/pulls you instead, for instance. But what about fast moving objects? If someone shot a bullet directly at a coinshot and the coinshot Pushed it, would the bullet or the coinshot move? Is speed factored in?

[King's Twit he/him]

Speed is factored in, by way of momentum. Bullets travel very fast, but they are too light to have enough momentum to create a significant push-back on a steelpush

[Oversleep]

I favour the theory that Steelpushing/Ironpulling conserve momentum, so both mass and speed is factored in.

If we have person A shooting and Coinshot B, and A and B have the same mass, and Coinshot Pushes hard enough to stop the bullet completely, then he will be thrown back as far as person A while shooting. I guess I could figure out general formula, but not right know; factors would be Force of The push (I believe it's another formula depending on the burn rate and allomantic strenght), mass of the bullet, mass of the Coinshot, mass of the shooter, speed of the bullet. If any person is moving, then his speed is also important.

Good thing allomancy is basically vector physics

[King's Twit he/him]

I favour the theory that Steelpushing/Ironpulling conserve momentum, so both mass and speed is factored in.

 

I guess I was unclear. I meant that speed was a factor, because it is a part of momentum.

 

I think that momentum is conserved, as well.

[Copperkeep]

This is exactly what I love about the idea of double iron twinborn: Have a friend fire off a round from a high-powered rifle, store as much of your weight as you can, and tether yourself to the projectile at just the right moment. The result: Bullet Sledding. I'm a little skeptical about whether or not it's mathematically possible (I'm not really equipped to do the math myself, I'm afraid), but I can't help but think it just feels right. Let's be charitable enough to assume that this is possible, and that the protection iron ferrings have against being crushed by their own weight extends to not suffering any more harm from a fall than they would normally. (Allowing for the fact that whatever they land on, if they were compounding weight, is likely not absorbing the same way it would if they were at their ordinary weight.) There are still any number of ways that the person who decides to do this on a regular basis is embracing their identity as a "Deader" and likely to seriously injure themselves very frequently at the very least, between the G-forces involved in bullet-sledding and the general harm they do to themselves when they're gliding high in the sky at reduced weight, then suddenly pull themselves in the direction of a little bit of metal worn by someone on the ground and start compounding weight once they're already on a collision course.

 

Lord Ruler, now I'm imagining a full Feruchemist/Mistborn with Kelsier's level of control over Ironpulling and Steelpushing. Feruchemical iron to adjust their weight on the fly to manipulate motion even more precisely, compounded Zinc and/or Steel to go into full bullet-time with mental calculations, and you've got a lunatic demigod swimming through the air in a field of bullets flying every direction, casually twisting the trajectories of the ballistics around him, dancing with bullets and shrapnel in a no-man's-land.

 

There's a lot of math on how much weight you can store at once and how much effect a bullet's momentum has on the force involved in manipulating it with iron and steel allomancy, none of which I could begin to do and which I confess feels a little suspect, but... if you could get away with fudging it just enough to allow this, wouldn't you?

 

It helps that, from what I remember, Wax can't usually completely reflect a bullet back the direction it came, can he? So the force of their motion is enough that even with Wax tapping weight to boost the strength of his steel bubble, the bullets are sliding off course instead of arcing backward? Or am I misremembering?

[Eagle of the Forest Path he/him]

It helps that, from what I remember, Wax can't usually completely reflect a bullet back the direction it came, can he? So the force of their motion is enough that even with Wax tapping weight to boost the strength of his steel bubble, the bullets are sliding off course instead of arcing backward? Or am I misremembering?

 

That's because steel pushes out in a straight line from a single point on Wax's body.

 

If the bullets aren't traveling directly towards Wax's center of gravity, it's impossible to push them back along their original trajectory.

[Charononus]

So we know Pushing and Pulling have clear rules. Anything more massive than you pushes/pulls you instead, for instance. But what about fast moving objects? If someone shot a bullet directly at a coinshot and the coinshot Pushed it, would the bullet or the coinshot move? Is speed factored in?

Pushing and pulling seem to use very basic physics.  Force = mass x acceleration  When pushing on a bullet the acceleration change is greater than pushing on a bullet that is just sitting on the ground,  but it's mass is such that it doesn't really matter.  Now in the scifi setting if an idiot mistborn tried to push on something fired out of some kind of magnetic accelerator cannon,  I would predict bad things happening to the mistborn.

[Copperkeep]

That's because steel pushes out in a straight line from a single point on Wax's body.

If the bullets aren't traveling directly towards Wax's center of gravity, it's impossible to push them back along their original trajectory.

I don't mean along their original trajectory. I mean that, from what I remember, he doesn't push them hard enough to force a bullet that was aimed at him to arc and fly off in a direction away from him. And I'm guessing that even a bullet aimed perfectly at his center of mass would be slowed, but not stopped or redirected backward.

If he were pushing them hard enough to change their course and send them flying directly away from him, then any bullet that appeared to just slide off course would be one that had already missed him before he started pushing on it (or was already going to miss him by a wide margin)- bullets actually aimed to hit him would instead ricochet back in the general direction of the shooter, possibly at a very oblique angle depending on what part of him they were aiming for.

Then again, if you *could* push that hard, then anyone who tried to shoot him at close range probably *would* be hit by their own ammunition if they were aiming for anything close to his center of mass.