Is an Iron Feruchemist's Energy Conserved? Could the Lord Ruler fly?

[Eric]

@Eric, good point about a diamond's brittleness. I had forgotten to take that into account. However, even though you mentioned the key concepts, you totally missed them. What stops a bullet is hardness and elasticity, primarily. What saves a person in a car crash is mass. That is why you were wrong.

Hardness and other factors are important in a car crash, but the major damage comes from a massive object transferring its kinetic energy to a less massive one. Because of the mass differences, the energy produces more damage. Equalize the masses, and the two objects will fair similarly. Increase the mass on the lesser object significantly, and the damage to it is reduced. Indeed, increase it enough and the damage from this transfer of energy can be largely negated. All the other damage still remains, of course.

Bullets function along the same way. They cause damage by transferring kinetic energy from a more massive object (a lead alloy bullet) to a less massive bit of flesh. But wax can increase his mass, so he can negate that damage to a decent extent. However, bullets cut into the skin, and cutting, though it involves mass, has more to do with hardness, elasticity, etc, which tapping "weight" doesn't influence. Thus, while Wax should be able to survive the punch of a bullet better, they are still going to cut him, they'll still cause him to bleed, etc.

I'm beginning to think we're talking across one another. The added weight/mass doesn't make Wax harder or more elastic. When a bullet or a car strikes a person, the initial damage is determined by those factors. Secondary damage from a car crash is taken from being thrown, which weight and mass will affect to a greater degree. Which is why I said storing weight to a massive degree might help, as you take all that energy as acceleration before it has a chance to overcome the elasticity of tissue and hardness of bone, and turn it into motion which can be bled off through drag.

And since we know that storing weight actually stores mass (as flying, which Sanderson confirmed, wouldn't work with weight but does with mass), it makes perfect sense that Wax could survive the impact of a car but still get cut by bullets.

Why does flying not work with weight instead of mass? Honest question, as this is further outside my comfort zone of what I remember from science classes. It seems (again, from mostly a layperson perspective) to imply that all flying machines work in any gravity, but one could easily infer that if there is less force acting on an object to keep it immobile (drag, gravity, or even anchors), it becomes easier to move in any dimension. Flight seems like it should be affected by weight.

Or, to put is another way, mass should help him endure crushing wounds, but not piercing ones.

Actually, tapping mass should make the bullet a little worse, in that it will definitely transfer all its energy to his body (more massive cells should drag on the bullet more, causing it to slow more, and reduce the chance of it exiting). It might be that storing "weight" would actually help survive bullet wounds, because the bullet it more likely to pass through the body easily, and thereby not fully transfer its energy.

Same as my stance about the car above.

As for cotton candy, interesting idea. I am not entirely sure, though, as you'd have to line up so much cotton candy to create enough drag that I might expect gravity to finish the bullet off first.

Potentially true. However, there's a way test this that eliminates gravity as the primary slowing factor. We just need someone to stuff a long vertical tube with a literal ton of cotton candy and fire a bullet down into it. That sounds so cool. Mythbusters would love it.

But all of this contradicts Wax's statement that it doesn't affect bullets striking him. Yes, it is entirely possible for him to be wrong, and it's a tactic used by Sanderson before, but the statement used as an assumption leads directly to the conclusion I made before. (Even then, I acknowledged it as physics-defying.)

@Satsuoni: Genius post. Also, #5 - Hydrostatic shock. Another one of my pet science items to read about; I haven't found serious evidence linking it to complications of any of the situations we're talking about. It's certainly a potential danger, but the way the valves in the veins and the pressure of the arteries work, it seems like you need lethal levels of impact before it becomes an issue anyway. Barring aneurism, naturally.

[Thought]

I'm beginning to think we're talking across one another.

Sounds like it.

As for why mass, not “weight,” has to be stored for flying to work, the reason is simple: “weight” isn’t a thing itself but the interaction of two other things (mass and gravity, or W=mg). If W decreases when an iron ferring stores, but m remains constant, then we know that g is what must be decreasing. So, if an iron ferring isn’t storing mass, they must be storing gravity’s influence on him or herself. The problem is, in order to fly, an iron twinborn would have to not only compensate for gravity, they’d have to overcome it. How is upward acceleration obtained? Well, by pulling on the counterweight. But, because for every action there is an equal and opposite reaction, by pulling himself up, he also pulls the counterweight down. Well, he pulls is back up, then. Except that the forces this time will be the exact same as the forces from the other pull. The counterweight accelerates the twinborn downwards just as much as it had accelerated him upwards. And, throughout that all, gravity is still effecting the counterweight at the very least. Thus, sustained flight is impossible.

In contrast, by changing mass, a twinborn can change every interaction of forces (F=ma), resulting in a net acceleration of “up.” A twinborn increases mass, pulls on a counterweight, and it goes shooting up while he is pulled downward by the same force. Because m is different between the two objects, even though the force is the same, the acceleration will be different as well. So, with a lot of mass, the twinborn accelerates downward just a little, while the counterweight accelerates upward a lot. Twinborn stores his mass instead and pulls again. This time the reverse: the force remains the same, but the counterweight is pulled downward with less acceleration than the previous interaction, and the twinborn upwards with more. Thus, he flies!

Of course, storing “weight” might actually store both mass and gravity. The point is just that storing weight has to store mass, not that it can’t store gravity as well.

But all of this contradicts Wax's statement that it doesn't affect bullets striking him.

Perhaps we’re still talking across one another? Wax says that bullets still cut him, even when he taps his metalmind. You said that the quote proves “weight” doesn’t protect him from impacts. Yet, my point was that bullets cause damage in two ways, one by cutting into the person, and the other by transferring kinetic energy through impact. Even if tapping weight helps him resist kinetic energy, it wouldn’t help him with the piercing damage. Thus, Wax’s statement remains true regardless of if he taps mass or not.

[Oudeis]

I wish this discussion had diagrams...

[happyman]

Perhaps a simple example will explain the relevant differences:

Mass is what you have the same of no matter where you go. In orbit, on the moon, on Jupiter, you have the same mass. In normal physics, it is what determines your acceleration in response to given forces. In F=ma, m is the mass.

Weight is the total force that you feel due to gravity. You have less weight on the surface of the moon than you do on Earth. On an earth-like planet, it can be approximated as F=mg, with 'F' the weight, 'm' the same mass as in F=ma, and g being planet- and surface-dependent.

Another important concept is pressure. Pressure is the force per unit area. Pressure is typically what causes slicing damage; the total force is not very high, but it is only on a small part of the material. The material gives. A little extra mass in the part that gives would technically increase its resistance, but likely not enough to make a life-saving difference.

Changing mass would be consistent with the statements: "bullets still go through me" and "I weigh less". It would also be consistent with the statement "Bullets, on average, tend to do less damage, as do long falls. But bullets are still plenty dangerous, thanks the same."

Changing weight (e.g. the lashing with the planet) would also keep the first two statements, but the third would become false; bullets would be exactly as dangerous as before.

Long falls, on the other hand, are more complicated.

[Eric]

Chiming in later than I wanted to because I lost connectivity while trying to post last night.

Sounds like it.

<snip>

Of course, storing “weight” might actually store both mass and gravity. The point is just that storing weight has to store mass, not that it can’t store gravity as well.

Okay, that makes sense now. Thank you!

EDIT: Actually, there may be another (really wonky) way it could work. Gravity is (G*m1*m2)/(d^2), yes? If storing 'weight' actually stores 'proximity', it would increase d. This seems very unlikely for three reasons; 1) the body can handle the change in weight, which it shouldn't be able to if you aren't utilizing mass on some level, 2) the gains and losses are relatively minor compared to what you'd expect from an exponential function, and 3) tapping enough 'proximity' to reduce d to 0 would create effective weightlessness, which is really weird compared to how it normally works. But it could have interesting effects on gravitational time dilation and perhaps the FTL built in to the metallic arts, so it might be worth considering anyway.

Perhaps we’re still talking across one another? Wax says that bullets still cut him, even when he taps his metalmind. You said that the quote proves “weight” doesn’t protect him from impacts. Yet, my point was that bullets cause damage in two ways, one by cutting into the person, and the other by transferring kinetic energy through impact. Even if tapping weight helps him resist kinetic energy, it wouldn’t help him with the piercing damage. Thus, Wax’s statement remains true regardless of if he taps mass or not.

My point is that 'cutting' isn't different from 'impact' when dealing with bullets. The 'cutting into' is achieved by imparting kinetic energy in sufficient amount to overcome the resistance of the tissue (happyman explains this really well, so I'll leave it at that). I'm therefore confused as to why the distinction exists; I think this is probably the part where we keep missing one another. We're pretty much entirely on the same page now.

Edited January 9, 2013 by Eric

[Phantom Monstrosity]

The thing is... increasing your mass *does* decrease impact depth.

There's a nice diagram on that wikipedia page... but basically, when something like a bullet is penetrating another body, the momentum gets fully transferred after it displaces its own mass of the target. It's a very good approximation for bullets.

So something seriously screwy is going on with this, and it's worth watching.

Edited January 9, 2013 by Phantom Monstrosity

[Thought]

I'm therefore confused as to why the distinction exists...

My justification, at least, is that because the "cutting into" damage of a bullet isn't its only effect, and it is governed by different qualities of the thing being hit than the other damage.

The ideal "bullet" will enter a person's body, go almost all the way through, but not leave the body. That maximizes all forms of damage to the individual. A bullet that does exit the body is wasting its energy, and is thus "unideal."

A hard, high-velocity, somewhat-massive-but-not-nearly-as-massive bullet could cut all the way through a body, cause all the same cutting damage as a less-velocity-more-massive bullet that doesn't leave the body, but ultimately leave a person in better shape.

While it's all related to kinetic energy eventually, the amount of that energy diverted strictly and solely to cutting is relatively minor and localized primarily to the cavity the bullet creates (if I understand it correctly, and I make no claim I do, the "cutting" creates a temporary cavity, while the rest of the effects is what creates a permanent cavity). That, of course, can still puncture veins, arteries, muscles, vital organs, etc. But all that cutting damage isn't effected that much by mass differences. The trauma to tissue surrounding the cavity is more related to mass, as is any breakage of bones (and thus damage to organs so protected).

So, related, but different. Thus, Wax being able to be cut by bullets even when he's at a higher "weight" doesn't mean that "weight" must be affecting something other than mass, which is what I read your original comment to mean.

As a side note, I like your idea about the gravity of "weight" possibly also influencing time dilation, though I can't say I fully understood your comments thus.

[Eric]

My justification, at least, is that because the "cutting into" damage of a bullet isn't its only effect, and it is governed by different qualities of the thing being hit than the other damage.

Okay. There's our disconnect. Insofar as I'm aware, the cutting *is* the only effect.

The ideal "bullet" will enter a person's body, go almost all the way through, but not leave the body. That maximizes all forms of damage to the individual. A bullet that does exit the body is wasting its energy, and is thus "unideal."

This is absolutely true. (Well, it doesn't need to go 'almost all the way through' to be ideal, just remain inside where the vitals are.)

A hard, high-velocity, somewhat-massive-but-not-nearly-as-massive bullet could cut all the way through a body, cause all the same cutting damage as a less-velocity-more-massive bullet that doesn't leave the body, but ultimately leave a person in better shape.

I'm right with you up to this point.

While it's all related to kinetic energy eventually, the amount of that energy diverted strictly and solely to cutting is relatively minor and localized primarily to the cavity the bullet creates (if I understand it correctly, and I make no claim I do, the "cutting" creates a temporary cavity, while the rest of the effects is what creates a permanent cavity). That, of course, can still puncture veins, arteries, muscles, vital organs, etc. But all that cutting damage isn't effected that much by mass differences. The trauma to tissue surrounding the cavity is more related to mass, as is any breakage of bones (and thus damage to organs so protected).

The piercing of the bullet does create a relatively small cavity. What creates the larger cavity (neither are really 'temporary' or 'permanent', as both can potentially be healed by remain until then) is typically either deformation of the bullet (in hollow point or fragmenting rounds) or tumbling (most everything else). I think the tumbling is what you're thinking of as a non-cutting type of damage, but it really is. It's just cutting with the bluntest possible parts of the round, which means a more ragged, wider wound. It's still the exact same concept and energy, but no longer focused on the tip of the round. Hollow points, of course, increase surface area to bleed off more energy into the target, achieving the same basic effect. Fragmentation increases surface area and spreads out like shot, but only after it hits the target, and thus achieves the greater surface area without sacrificing the cutting ability as much. (It can produce deeper ragged wounds, but isn't as good against armor, which is why they aren't used all the time.)

So, related, but different. Thus, Wax being able to be cut by bullets even when he's at a higher "weight" doesn't mean that "weight" must be affecting something other than mass, which is what I read your original comment to mean.

Ah. I actually meant that it seemed to be selectively ignoring the mass increase (hence the addendum "In a weird, physics-ignoring way..."), in the same way the the time bubbles don't actually cause red/blue shift like they should. (Which is sort of a precedent for minor deviations from the laws of physics like this would be.)

As a side note, I like your idea about the gravity of "weight" possibly also influencing time dilation, though I can't say I fully understood your comments thus.

I'm not sure myself how it might help, I just think that it might provide some insight. The short version is that more massive two objects are and the closer the centers of those two objects are, the greater the force of gravity exerted. The closer you are to a center of gravity, the slower time passes for you (per relativity and confirmed via experiment). If you could couple that slowing of time with some of the acceleration tricks proposed in the FTL threads, it might be more effective.

For example, say you have a car going 60 km per hour, as measured by the speedometer in the car. Say the car is made the center of a gravity source, and the driver now experiences time at half the speed that those outside do. If one hour for those in the car equates to two hours for those outside, then those outside will perceive the car going 120 km/h, without any added energy being used. It's only a possibility (and an unlikely one, as I mentioned before), but it could explain a lot.

[Thought]

Okay. There's our disconnect. Insofar as I'm aware, the cutting *is* the only effect.

Aha! So, to my understanding (which isn't authoritative in the least: damnation it, Eric, I'm a historian, not a doctor!), ballistic trauma can be separated into cutting, crushing, stretching, and tearing aspects. Stretching damage, for example, is caused by the creation of the cavities as it pushes otherwise uncut tissue into an abnormal shape. Likewise, there's a lot of crushing damage that surrounds the wound. And so on.

[Eric]

Okay, there we go. They are all part of the same process, in precisely the same way that they are all part of the same process as a pair of scissors cutting paper (which your examples of stretching and crushing can be readily seen if you look), so I wasn't separating them. But, after looking it up, people do indeed.

"Cutting tissue is far more efficient than crushing it, and crushing it is far more efficient than tearing it apart by stretch (as in temporary cavitation)." -'What's Wrong With The Wound Ballistics Literature, And Why', M. L. Fackler, M.D., Letterman Army Institute of Research

The author is specifically talking about why energy output alone is a poor indicator of the damage of a wound, but it's a nifty quote to support your divisions.

"The wound area can be divided into the central primary track (the permanent cavity), which depends on tissue elasticity; the contused muscles near the tract; and the outer concussion area (changing congestion), which inversely depends on the transferred energy (relatively low if any, in low-velocity “civilian” gunshot wounds which may explain why it rarely requires a full wound exploration." -'Chapter 2: Wound Ballistics and Tissue Damage' from 'Armed Conflict Injuries to the Extremities: A Treatment Guide', Nimrod Rozen and Israel Dudkiewicz, Eds. A. Lerner & M. Soudry

(Contains graphic images. Not safe for work, children, or for those with weak stomachs.)

This sort of segregation is probably where my disconnect came from. These are closer to what I had learned in the past when researching this sort of thing before, and they're all described as essentially regions of the same effect.

Woot! I learned something today! Many thanks, Thought!

Edited January 10, 2013 by Eric

[happyman]

Now that I see Eric's latest post, I am thinking that efficiency really is the key question, and how it relates to storing weight/mass/whatever.

The thing about bullet wounds is that (unless the bullet actually goes through you) all of the energy gets transferred into the person shot. There are different ways that that energy can be delivered, though. Some of it goes into heat. Some of it gets translated into destroying chemical and physical bonds (e.g. ripping organs apart, breaking bones, etc). Some of it gets converted into the kinetic energy of the entire person. How much it does of each would depend on how storing/tapping affects the physical properties of the person hit. They also would affect how likely the person is to survive the wound.

For instance, if storing/tapping weight just changes the force of gravity, but nothing else, bullets would have exactly the same effect on the feruchemist as on a normal person.

If storing/tapping weight changes the mass of the person, and all accompanied parts proportionately, it would do less damage overall (because feruchemical mass change in this case does not conserve energy, and any resulting kinetic energy transfered, either as heat or total kinetic energy, would be experienced as less by the feruchemist), but the proportions which affect the transfer would also probably change.

Basically, it comes down to how much the other fundamental forces which hold the atoms/molecules/cells together react to the change in mass. Since at this point, I'm pretty sure that the cosmere doesn't act like the real world at this level (see: surges on Roshar) I think we should conclude that (a) Brandon's presentation isn't necessarily nuts, but (B)/> isn't necessarily like the real world, either.

Edited January 10, 2013 by happyman

[Kurkistan]

<snip>

Basically, it comes down to how much the other fundamental forces which hold the atoms/molecules/cells together react to the change in mass. Since at this point, I'm pretty sure that the cosmere doesn't act like the real world at this level (see: surges on Roshar) I think we should conclude that (a) Brandon's presentation isn't necessarily nuts, but ( B ) isn't necessarily like the real world, either.

The oddness of surges seems pretty well defined, as far as I can tell. The Basic Lashing takes advantage of the Spiritual nature of connections between everything, of which gravity is only another connection, to be manipulated in the Spiritual Realm. All the forces, then (atomic/molecular bonds, gravity, etc.), likely rest in the Spiritual Realm. They are the same connections as in the real world, but can be manipulated separately from their Physical trappings. I'm not sure what this entails for Iron Ferrings, but it's a good thing to keep in mind going forward.

Edited January 10, 2013 by Kurkistan