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Perpendicular Allomancy

You have an allomancer skilled enough to apply forces to parts of objects rather than the entirety of an object. He wants to pick up a brass idol from a pedestal without getting close (scary spiders are at the base of the pedestal). The idol has a mass of 25 kg and its height is 1/6 of the distance between the allomancer and the idol. The bottom of the idol is level with the allomancer's center of mass. For simplicity, assume that gravity on Scadrial creates a downwards acceleration of 10 m/s. In order to overcome gravity, the allomancer needs to exert more than 250 N of upwards force on the ball. Let's double it and say that they want to produce 500 Newtons upward. In order to apply that much vertical force by pushing on the top of the ball, the total force of the push must be (500/sin(9.824°) = 3041.38) N. But this push also results in a perpendicular force of 3000 N away from the allomancer. If he pulls on the bottom of the idol to counteract this force, then the net forces will lift the idol straight upwards. (Also, the idol will start spinning like crazy, so if the allomancer wants to keep applying the force, he needs to be good at juggling his target points.)



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They would need F-zinc or F-steel in order to change their push/pull location that fast, IMO. I'm not gonna attempt the math, but that thing would probably be spinning 10k+ RPM.

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Jofwu

Posted

I don't get the sense they can Push/Pull ALL of an object's mass out of alignment with the center of that mass, however. In other words, if you want to Push only at one edge of the object, you can only Push the mass located at the edge of the object. If you can manipulate the strength of a Push/Pull freely then this isn't TOO big of a problem. But the books suggest they don't have that level of control, and that the strength is a function of how much mass you're Pushing/Pulling.

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Young Bard

Posted

Yeah, I was going to say something similar to what Jofwu said - I think there's a theory out there (I don't believe it's been confirmed) that says we've only ever seen one 'line' coming from a given object because of Cognitive Realm stuff, where the object being Pushed/Pulled perceives itself as one object, so you would only be able to push-pull the object. It's a really neat idea, though - if it were some sort of elevator specifically designed to have two metal plates on the top and bottom, it might work?

Actually... how much torque would this produce? You're Pushing the top and Pulling the bottom, so my 'elevator' idea wouldn't work either (at least not one I'd want to stand on), since it would end up spinning wildly as it rises.

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bacontime

Posted

On 4/15/2019 at 5:14 PM, SwordNimiForPresident said:

They would need F-zinc or F-steel in order to change their push/pull location that fast, IMO. I'm not gonna attempt the math, but that thing would probably be spinning 10k+ RPM.

Say the radius of the idol is 10cm. (That's actually a bit too large for 25kg of brass, but eh, round numbers.) The moment of inertia of a solid ball is (2/5)*m*r^2, which works out here to 0.1 kg m^2.

The depicted forces apply 600 Nm/rad of torque.

So the  angular acceleration is 6000 radians per second per second. (Or ~57000 RPM per second)

In other words, it would take less than a second  for the surface of the ball to accelerate past the speed of sound. Hover juggling heavy objects is probably not possible without holding the bands of mourning.

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bacontime

Posted (edited)

As for the concern about pushing only part of an object: We see both Kelsier and Wax do this in canon. Also:

Quote

Kyrroti

If I were burning iron, where would the line point to on a steel hula-hoop?

Brandon Sanderson

For something like that, it would depend on the Steelpusher's power. For some, it would just be pointing generally toward the center of the hoop--but for skilled Steelpushers, they'd be able to see softer lines pointing in all directions around the hoop.

Skyward Pre-Release AMA (Oct. 12, 2018)

 

Edited by bacontime
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Ethan_Sedai

Posted (edited)

Now, I’m not an expert on physics-I’m not even out of high school yet-but I wonder at what point curveball physics would start applying and curving the path of the object.

also, excuse my bad drawing, but I think this might be more efficient:2BABD8B6-BF94-4828-940B-E086528D277A.jpeg.7ead9563d2ea4a1a50c8771176f6004a.jpeg

and it would work, because it is possible to Push and Pull from different points in your body, Vin does it when she Pushes the Vial of Atium from her belt to in front of her, then Pulls the bead into her mouth, and there are other examples, too, but I’m too busy trying to do this and statistics homework simultaneously.

Edited by Ethan_Sedai
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bacontime

Posted

16 hours ago, Ethan_Sedai said:

because it is possible to Push and Pull from different points in your body,

I totally forgot about this, but their are WOBs that seem to confirm that this works. And this way has the advantage of not causing the target to spin widely.

The downside of course it that it causes the torque to be applied to the allomancer. So they'd need to anchor themself to something solid and burn pewter to handle the strain.

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