Kuma can only repel things he can touch with his paws. If sand gets somewhere inside him that he can't reach, there shouldn't be anything he can do about it, at least with his DF power. Not that it really matters now that the fight is over.
But that's not quite true, since how could he have touched Luffy's fatigue? It's not tangible. The closest thing to it would be touching Luffy, and pushing out the fatigue. Likewise, I imagine he could touch himself (not in a dirty way, haha) and remove things that are in his own body.
Exactly that. Fatigue is non-tangible and there are no rules saying what it can and cant pass through. Sand is tangible, even as small fragments, but it's still sand and can't simply pass through his body to get out. It has to go the way it came, which is easier said than done. Also that Luffy had no control of his fatigue... other than adding to it. Where Croc control his sands... (of time)...
But we haven't seen that kind of limitation of Kuma's power, like you describe. In fact, we've seen the opposite. For example, he did not need to touch all the air molecules in order to compress them into a shock wave. It just was contained in a big paw shape. Likewise, Luffy's fatigue was just simply "pushed out" by Kuma's power, and contained in a big paw shape.
About the not touching, you're right. But Kuma's power is pushing, and not space-time ninjutsu. He can't make physical things move through other physical things.
That's because of the quality of air. He's always touching it. He doesn't have to run around touching the air molecules, because more just come to fill the vacuum.
Scientifically, that's not true. Particles of air (N2, O2, CO2) and particles of sand (SiO2) behave the same way, with air particles attracting each other more than the sand particles. I could get into a big discussion of physical science / chemistry, but that is totally not what One Piece is about! Oda keeps things pretty simple and straight-forward.
Wait, who said he could? That's not required. If the sand entered from somewhere, it can exit from the same place. From what we've seen of Kuma's powers, he can just touch himself with his hand, and push the sand back out (assuming he even needs to touch himself with a hand to do it, the sand would already be touching his body).
If it damages his gears, that'd be a problem. Moreover if he doesn't notice the tiny grains of sand.
It would have to be quite a small amount to be unnoticeable, and would need to be in there quite a while in order to cause significant damage. But I could see Croc slipping in a small amount to gum up the gears a little bit and slow Kuma down a bit in the battle.If it damages his gears, that'd be a problem. Moreover if he doesn't notice the tiny grains of sand.
BTW physics corner: particles of air don't really attract / repel, unless they're very close. The very-short-range repulsive force makes them pretty much the same as small hard rubber balls, which bounce off each other. The reason gas holds together is
a) it's in confined space
b) it's in a for example gravitational field
That means if there was no gravity, the atmosphere would immediately disperse.
SiO2, on the other hand, holds together by weaker intermolecular bonds. Grains of sand act like air particles (to a certain extent) in that they bounce off each other, but the effect is negligible due to much worse ratio surface/mass.
Not important, just force of habit
Actually, that's not right. (I guess we can talk about the physics after all, haha, as this is my topic of expertise.)BTW physics corner: particles of air don't really attract / repel, unless they're very close. The very-short-range repulsive force makes them pretty much the same as small hard rubber balls, which bounce off each other. The reason gas holds together is
a) it's in confined space
b) it's in a for example gravitational field
That means if there was no gravity, the atmosphere would immediately disperse.
SiO2, on the other hand, holds together by weaker intermolecular bonds. Grains of sand act like air particles (to a certain extent) in that they bounce off each other, but the effect is negligible due to much worse ratio surface/mass.
Not important, just force of habit
When I said he had to touch something to push it, I meant with his paws. We've never seen him push anything without touching it with his paws. Whether or not sand can be pushed out through a solid object is debatable, but not the necessity of some form of contact with his paws.
It (most likely is going to be) my field of expertise, too... nice to see someone else like this.
), but I'm sure about typical air.
Cool, good luck with it, do what you enjoy!It (most likely is going to be) my field of expertise, too... nice to see someone else like this.
Liquids (and gases) are fluids.
You're right about the polarizability causing intermolecular forces (London dispersion forces in case of air), but those are the very-short-range forces I was referring to. If you compare mean free path (order of tens of milimeters) to approximate distances from which non-negligible polarization arises (order of angstroms), you'll find out that polarization really only governs molecules when they're "colliding".
Viscous forces arise from forces between molecules, it's not good to put these together with elemental forces like London's or G. And internal gravitational forces are even more negligible than London forces. Take 2 molecules of N2 for example, at their mean distance, and calculate the ratio between energy of their field vs. mean kinetic. I get about 10^-30. Energy is not the best for comparison, but there's no doubt in this case. This is caused by both bodies having very low masses. In comparison, the same ratio for an N2 molecule close to the Earth's surface and Earth, vs. mean kinetic energy is 10^4.
So no internal gravity, and close range London dispersion (which btw drops much faster with distance than typical Coulomb force). Diffusion is right, but if there was no gravity, it'd be diffusion air-vacuum, which fits your explanation with sand, too.
I don't dare to definitely say much about how sand acts in comparison (what I said about that before were just "educated guesses"
I work on theoretical particle physics.
London forces are actually electromagnetic, so it's incorrect to arbitrarily separate forces into something you are calling an "elemental force," there's no such thing. We can talk about atomic forces (between atoms) vs. intermolecular forces (between groups of atoms). In the case of a gas or sand, we are looking at intermolecular forces.
