Shulou(Shulou.com)11/24 Report--

There is a case that proves that the sharpest object in the world cannot cut anything. We've all cut apples with knives, and it's obvious to us that knives are sharp. But if the tool is sharp, then it should be easy to cut things. So the phrase "the sharpest object in the world can't cut anything" sounds counterintuitive, so what's going on?

Like most other concepts, scientists try to pin down sharp definitions. The first object that may come to mind when hearing the word "sharp" is a knife, and studying the exact details of the shape and its geometric characteristics provides a starting point for us to define sharpness. If we zoom in on the blade, we see that it has a wedge shape. Intuitively, the "sharpness" of a wedge seems to boil down to two main attributes: how sharp it is and how narrow it is. Therefore, scientists created specific measures of "sharpness" and "narrowness" to try to define sharpness!

Starting with sharpness, if we expand the edge of the knife, we will find that the wedge tip does not shrink to an infinitely small point. Instead, it will eventually contract into a tiny curve. Think of this curve as forming part of a circle whose radius can ultimately determine how small the edge of the knife is. There's a word here called edge radius, which is our geometric way of describing the "sharpness" of a blade. A smaller edge radius means a smaller curve, and the knife edge is closer to the ideal perfect sharp corner shape.

But the edge radius is not the whole sharpness, because even knives with the same radius may have different thicknesses. Therefore, in order for Edge Radius to be useful, we must also identify the Narrow section. This is defined by what is known as the wedge angle: the angle between the two planes of the wedge. A smaller angle means a thinner wedge, which usually means a sharper blade.

If a blade has a fixed small wedge angle, the edge radius determines sharpness. For example, some surgical scalpels have sapphire blade edges with radii as small as 25 nanometers, which is equivalent to only a few hundred atoms! Because the blade is so sharp, scars left by sapphire scalpels actually heal faster than steel scalpels. In addition, the blade is made of hard sapphire, which is very durable.

But even these ultra-sharp sapphire scalpels are not the sharpest; a sharper blade is made of obsidian. Obsidian is a volcanic glass that can be made into blades with an edge radius of just 3 nanometers. That equates to just a few dozen atoms, making it one of the sharpest objects we know of. Today. We still use obsidian blades for certain types of surgery because their super-sharpness allows cutting without applying too much pressure. In fact, obsidian blades can even cut a single cell in half. So the edge radius and wedge angle combine to describe obsidian's incredible cutting power.

So, this gives us the illusion that defining sharpness is easy. Unfortunately, the geometric attributes we have discussed so far have some disadvantages, such as describing the sharpness of needles, since their tips also shrink to a curved surface, we can use the concept of edge radius. But unlike knives, they do not have two flat surfaces forming a wedge, so the wedge angle has no meaning here.

We can use other types of angles, but they all have their own problems. For example, for an injection needle, there is an angle between the inclined edge and the straight edge, known as the "bevel." A 2012 study found that placing multiple bevels on the same needle improved its ability to pierce the skin, which is important for reducing pain and improving efficacy. This goes against our intuition about sharpness.

As for edge radius, the smallest radius we have achieved on artificial tools is tungsten nanoneedles. It is a scanning tunneling microscope probe that generates tiny electrical currents that jump between the needle and the surface. By doing so, the tip can identify the location of individual atoms on the surface and help us build an image of what the material looks like. The tip of this probe is only one atom wide, and we can't get any smaller than that. It is also because of this ridiculously small radius that Guinness World Records declares tungsten nanoneedles to be the sharpest man-made object in the world.

But as we said at the beginning, this needle cannot cut or pierce anything! An object that is only one atom thick is so brittle that even if it has super "sharpness," it will not improve the cutting ability or piercing ability of the needle. If we try to put any pressure on it, it will break.

And it's not just the tungsten nanoneedles that are the problem. Those obsidian scalpels we mentioned earlier aren't going to be used all the time either, because they're also brittle and risk breaking if the surgeon isn't careful. Therefore, sharpness does not necessarily apply when describing the ability to cut or perforate. It describes only the geometry of an object, not its function.

This article comes from Weixin Official Accounts: Vientiane Experience (ID: UR4351), by Eugene Wang

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.