Physics question involving heat and force.

[Traab]

Ok, so ive watched a few of "Because Science" videos where they are sponsored by the new mortal kombat game. For those who dont know, he basically does episodes seeing if the crazy stuff that happens there COULD happen in reality, as an example, sub zero and his ice ax. The one I just watched is testing scorpions fatality where he cuts you in half with a red hot chain. Now, they "established" that it wouldnt work but the comment section is ablaze with arguments on all the ways they messed up, the question on my mind is, one of the arguments is that scorpion is clearly exerting plenty of pressure and force on the chain where they just draped it over the material they wanted to burn through. For the math wizzes out there, how much of a difference would it have made if instead of just resting on the material, it was wrapped around and pulled tight?

For the record, these episodes are way more cringey in content than normal imo, it just feels sloppy as heck, likely because he had to crank them out in short order, so dont sneer at him too harshly.

[Lord Torath]

If it is swinging fast enough, a non-red-hot chain can cut you in half. Is the question whether or not Scorpion (a human ninja, with presumably human strength) could swing that chain fast enough to cut someone in half? I'm going to say "no". He could wrap it around your waist, but I seriously doubt he could cut a human in half.

My personal thought is that it doesn't matter whether the chain is glowing red-hot or not. The chain will have to pass through the body quickly enough that there will not be time for any meaningful transfer of heat from the chain to the body (I haven't seen video of Scorpion using this move, but I assume it takes no more than a second or two). Human bodies are mostly water, and water has one of the highest specific heats of any substance. It takes a LOT of energy to warm water up.

Wait, Scorpion cuts you in half lengthwise? Yeah, no. A chain is too blunt to cut cleanly through bone. And there's a LOT of bone to cut through: skull, neck , spine, sternum, pelvis. Maybe if you had 200 tons of force behind it. But unless you perform this cut in a thousandth of a second, you're going to crumple the person, not slice them in half.

[Traab]

If it is swinging fast enough, a non-red-hot chain can cut you in half. Is the question whether or not Scorpion (a human ninja, with presumably human strength) could swing that chain fast enough to cut someone in half? I'm going to say "no". He could wrap it around your waist, but I seriously doubt he could cut a human in half.

My personal thought is that it doesn't matter whether the chain is glowing red-hot or not. The chain will have to pass through the body quickly enough that there will not be time for any meaningful transfer of heat from the chain to the body (I haven't seen video of Scorpion using this move, but I assume it takes no more than a second or two). Human bodies are mostly water, and water has one of the highest specific heats of any substance. It takes a LOT of energy to warm water up.

Wait, Scorpion cuts you in half lengthwise? Yeah, no. A chain is too blunt to cut cleanly through bone. And there's a LOT of bone to cut through: skull, neck , spine, sternum, pelvis. Maybe if you had 200 tons of force behind it. But unless you perform this cut in a thousandth of a second, you're going to crumple the person, not slice them in half.

Oh I fully agree with it failing on realism, my main question was, would it have gotten further wrapped around the target and pulled tight than just left resting on the body. Like, in the video it ignited the crotch on fire and did melt a little way through it, but not much, but would some guy hauling on it as hard as he could let it burn/melt its way in further?

[Mastikator]

Oh I fully agree with it failing on realism, my main question was, would it have gotten further wrapped around the target and pulled tight than just left resting on the body. Like, in the video it ignited the crotch on fire and did melt a little way through it, but not much, but would some guy hauling on it as hard as he could let it burn/melt its way in further?

The thing is that humans don't really melt, we're made out of water and carbon, carbon evaporates at 3620C which is well above the boiling point of iron.

Even if it was a tungsten carbide chain you'd have to continuously feed it with thermal energy to actually cut through a human using heat.

[warty goblin]

The thing is that humans don't really melt, we're made out of water and carbon, carbon evaporates at 3620C which is well above the boiling point of iron.

Even if it was a tungsten carbide chain you'd have to continuously feed it with thermal energy to actually cut through a human using heat.

The limiting factor on the ability to burn through a person is almost certainly going to be all the water they contain. Until you've cooked at least the local area dry, you aren't going to raise the temperature of flesh over 100 Celsius; and it takes a lot of heat to do that. Think of how long it takes to cook a steak to well done; and that's a small piece of already bled dry flesh.

[Knaight]

Assume 100% heat transfer. Using No. 80 welded steel chain (which is about as heavy as you get for light applications, which is a pretty heavy chain all told) there's a mass of 5 pounds per foot. For a 20' chain (which is about as long as I can justify as a weapon) that's 100 pounds. Call it 50 kg, to get this in convenient units. Red hot steel can be a good 800 C, which with optimal thermal assumptions has 0.5 kJ/(kg*K). Cooling that entirely to 100 C transfers 2500 KJ of heat. So, let's talk water. The latent heat of vaporization of water is 2260 kJ/kg. The specific heat is 4.18 kJ/kg. This lets me do some real convenient math, where if I assume someone is already at 42.5 C (hot, but not so hot it's totally infeasible) this heats and vaporizes 1 kg of water. There's more than 1 kg of water in the cross section of the person cut in half by the chain times the chains width, and that's without getting into thermal conductivities here (where heat transfers within the water far faster than from the chain to the water). It also involves ignoring everything but the water, starting with lots and lots of bones.

The chain being red hot is completely negligible in the context of it being a cutting tool here.

[factotum]

In fact, a thinner wire would cut better than the chain because it has less material to push aside. He could probably cut someone in half lengthwise with a sufficiently thin, strong wire, but such a thing would have to be made of SF material like Sinclair monofilament chain from Larry Niven's books.

[Chronos]

Quoth Mastikator:

The thing is that humans don't really melt, we're made out of water and carbon, carbon evaporates at 3620C which is well above the boiling point of iron.

We're not made of "water and carbon". We're made of water and carbon compounds. Carbon compounds have completely different physical properties (like melting point) than elemental carbon. Which is irrelevant anyway, because melting isn't the only way for heat to destroy a solid object, and most of those carbon compounds are flammable.

[Knaight]

We're not made of "water and carbon". We're made of water and carbon compounds. Carbon compounds have completely different physical properties (like melting point) than elemental carbon. Which is irrelevant anyway, because melting isn't the only way for heat to destroy a solid object, and most of those carbon compounds are flammable.

They're not flammable at temperatures below the boiling point of water*, and while you can get surface burns easily enough with the hot chain you're not going to get meaningful amounts of additional energy out of the chemical reactions of flesh burning. Elemental carbon is completely irrelevant here, but burning is similarly pretty irrelevant in the context of cutting. There's a reason that actual burn/cut mechanisms generally provide continuous heat.

*Fluorine atmospheres and the like aside.

[Kato]

I'll agree with what seems to be the majority: cutting people with heat just isn't the same as with e.g. metal. Wet stuff acts differently and were plenty wet. I'm a bit less sure if we were talking just bone / skeleton.
Of course higher force would help a lot and if you used something that delivers more energy per second, like a laser, you could make it work with just the heat.

[Traab]

Ok thanks all, that answered my main question of if yanking his chain would have made a difference.