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I was thinking in a character who has a...kind of Steam powered Chainsaw, and a sword, what make them special is because the blades of the chainsaw are one-dimensional, same with the sword, they are made of iron.

I was actually curious what could they cut and what not, or anything with that level of edge can cut everything ? and, if that is the case, Could a one-dimensional paper cut with "ease" a Steel spoon ? Or my Iron Chainsaw could cut a armor made of Nuclear pasta ? ((just assuming that somehow someone manage to "deactivate" the gravity that thing should apply over everything, also assuming that material is solid, this is just a crazy totally hypothetical scenario, i actually don't want that kind of armor in my story))

Or be one-dimensional actually would made these thing very fragile ? if that is the case, just the edge part is one-dimensional (With one dimensional i am referring to something with thickness of one atom, only less if is scientifically possible) I would really appreciate it if someone clarify my doubts, thank you

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    $\begingroup$ Assuming your blade didn't snap, it could, but the cut would be so fine, that the two parts would recombine as soon as the blade was past. For all practical effect, your blade would simply pass through solid objects as though it didn't exist. $\endgroup$ – nzaman Mar 16 at 7:30
  • $\begingroup$ reddit.com/r/explainlikeimfive/comments/2lsgdf/… $\endgroup$ – Ville Niemi Mar 16 at 7:31
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    $\begingroup$ Its called a "monomolecular edge". Graphene for example would fit the bill as its a monolomecular structure 1 Carbon atom wide and a lot stronger than steel. Unfortunately the thinner the edge the easier it is to break the edge as well. $\endgroup$ – Demigan Mar 16 at 11:20
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    $\begingroup$ Chainsaws (or any kind of saw) don't work the same way swords do. Swords just slice (or stab). The cutter teeth of a chainsaw cut thin strips of material, and remove the material from the cut. So a 1-D chainsaw wouldn't work as a chainsaw. $\endgroup$ – jamesqf Mar 16 at 17:42
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    $\begingroup$ "One dimensional" is not the same at all as "thickness of one atom". $\endgroup$ – StephenG Mar 16 at 19:13
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Ok, assume you have wire that's a single atom wide. You have each atom bonded with only two atoms left and right of it. If these bonds are weaker than the bonds of the material you want to cut, well, there goes your wire. As such, no cutting steel with a 1D paper "blade".

Next point is force. You need to supply forward force strong enough to move your "blade" through the material. When you cut something with a wire, all that forward force comes from the wire tension times the curvature of the wire. A straight wire simply cannot have any forward force to cut. The tension of the mono-atomic wire is limited by the strength of its chemical bonds, again. This puts a strict limit on the width of the material you can cut. If the material to be cut is to wide, you either cannot apply enough force to push the wire through, or your wire snaps. You may get away with cutting some soft stuff in the range of millimeters, but you won't be able to cut anything macroscopic.

Finally, if you try to cut wet stuff, well that's difficult. Since your "blade" is only separating stuff by the width of a single atom, the wet stuff will just rejoin after the "blade". Thus, you'll be able to pull your "blade" right through most living cells, and the cell will live on just like nothing happened. This does not apply to muscle cells where severing the structural proteins would cut the muscle, but your muscle cutting ability is already heavily limited by my second point above. Same story for bones. Anything else should survive your "cut" just fine.

So, bottom line: While a 1D blade sounds very dangerous, it's actually not dangerous at all.

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No. First off, there are no truly one dimensional structures, but if you assume there are: Cutting requires getting into the material and separating it. You need some sort of wedge for that, the tip digs into the material, and the flanks move the material apart.

Sharpness only helps to some degree, it makes it easier to get some indent for the wedge to move in, but beyond that a sharp edge mostly ensures a cleaner, less jagged cut.

To separate a chunk of metal, you need to provide enough force to drive in the wedge, and move the material out of the way.

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  • $\begingroup$ Such a wedge is called a blade. You can't cut glass with a razor blade. Not even if you sharpened the edge to be one atom thick. $\endgroup$ – chasly from UK Mar 16 at 11:11
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A one dimensional thing would be a row of atoms. Think of it like a very thin rope. it could only work to transmit tension, any other load would make it nonfunctional:

  • compression: any tip load would buckle the line, ruining it
  • shear: same here, the line would simply bend and be useless
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If we assume that the blade has the structural integrity to retain it’s shape, it would be useful but could not cut through everything.

Even if the edge of the blade is a single atom thick, it doesn’t mean it will be able to cut through steel. The blade still has some measure of width, no matter how small, which will mean it will get stuck in the material it is trying to cut through. This is because it has to force apart the steel and push through it but, because of the friction generated, it is likely to get stuck. If the whole blade was this thin, it might cut through steel but, as others have mentioned, wounds caused would not be very thick and might reseal after the blade passes through.

Something else to consider is how long he blade will retain it’s edge. He thinnest edge used on a blade historically was made of obsidian, also called volcanic glass. The edge, if made correctly, can be a few nanometers in thickness (which is so fine you can’t see the very edge with the human eye) but even this can’t cut through steel. The reason being is that, as soon as the blade comes into contact with any material, it will start to dull.

This is true for any material, how well something retains an edge is a key component in the manufacturing of swords. It is also why we aren’t using paper in swords, although it can be very sharp on the edges, it will very quickly dull and won’t have the same level of sharpness. If we assume your blade is made of iron, as stated in the question, it will have a better edge retention but the idea still applies. Whilst it will still be very sharp after the first cut, it will no longer be one-attom sharp.

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