# What is Knife: Definition and 25 Discussions

A knife (plural knives; from Old Norse knifr, "knife, dirk") is a tool or weapon with a cutting edge or blade, often attached to a handle or hilt. One of the earliest tools used by humanity, knives appeared at least 2.5 million years ago, as evidenced by the Oldowan tools. Originally made of wood, bone, and stone (such as flint and obsidian), over the centuries, in step with improvements in both metallurgy and manufacturing, knife blades have been made from copper, bronze, iron, steel, ceramic, and titanium. Most modern knives have either fixed or folding blades; blade patterns and styles vary by maker and country of origin.
Knives can serve various purposes. Hunters use a hunting knife, soldiers use the combat knife, scouts, campers, and hikers carry a pocket knife; there are kitchen knives for preparing foods (the chef's knife, the paring knife, bread knife, cleaver), table knives (butter knives and steak knives), weapons (daggers or switchblades), knives for throwing or juggling, and knives for religious ceremony or display (the kirpan).

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1. ### B Question about collisions -- Knife point piercing a ball of clay

I have a question regarding the collision of two objects, specifically something heavy falling on something with a point. For example, if a 50lb ball of clay fell from 10 meters onto the point of a knife, would the knife's point have to withstand the entire force of the clay before the blade...
2. ### Can You Solve This Motion Problem Using a Simple Trick?

##v^2=u^2+2as## ##v=10m/s## Again ##v^2=u^2+2as## ##a=25 m/s^2## So ##F=(200*25)/1000## ##F=5 N## Wrong answer!
3. ### Is Throwing a Knife with No Spin Actually More Effective?

They say that a rotating knife thrown is more dangerous than a knife thrown straight I find it weird If the knife is rotating, it will experience more air drag than if thrown straight which will also depend on plane of rotation(For some reason, I don't know, it experiences more drag if...
4. ### Fingernail not tough enough for opening tools on a Swiss Army Knife

Is any tool available for a person to use instead of putting their weak finger nail into the groove of one of the functions of a swiss army knife or victorinox knife in order to open that function? Some of our nails are just not tough enough to put into those grooves to pull the function out...
5. ### Is My OTF Knife Configuration Safe for Everyday Carry?

Hey guys, brand new here but looks like I'm in the right place :D I've got an OTF knife (a.k.a. "out the front," where the blade ejects straight out from the handle) that is held in the closed position with 1 lb, 12 ounces of magnetic force. I.e, upon measuring it takes 1 lb, 12 oz. of finger...
6. ### A Metallic Hydrogen as a knife blade

I have never posted a Q here before, but as an old knife and swordmaker, when I saw this article: https://phys.org/news/2019-06-french-scientists-metallic-hydrogen.html It suddenly piqued my interest: IFF one can create a large enough, meta-stable crystal of metallic Hydrogen, and were able to...
7. ### Newton's laws of motion problem -- Knife penetrating cardboard

An open knife edge of mass 200 g is dropped from height 5 m on a cardboard. If the knife edge penetrates distance 2 m into the cardboard, the average resistance offered by the cardboard to the knife edge is:
8. ### Answer out by 2 orders of magnitude....how?

Homework Statement A tradesman sharpens a knife by pushing it against a grindstone with a given applied force. The grindstone is 28kg, 15 cm in radius, is originally going at 200 rpm but is slowed down to 180 rpm over 10 s by applying the knife. The coefficient of kinetic friction is 0.20...
9. ### What is the best knife blade metal for long-lasting sharpness when cutting meat?

hi you'al, i hang in a knife forum and there is a lot of discussion on what steel is "best" for knife blades..latest fad/dream steel is some power made to steel from Hitachi some of what i wander is the "powder" made no for these steels and what adds to the properties of the steel the...
10. ### What's the sharpest knife on earth?

I was thinking about the principle of energy density and how sharp knives cut so easily because their surface areas are tiny and thus any force applied to them is imparted on this tiny area. So my question arises, does anyone know just how sharp the sharpest knife/ sword is? Let's no discuss...
11. ### What is the purpose of the groove in this knife?

It is not a folding knife. And it's too small to act similar to a "Granton Edge" that prevents slices from sticking. https://scontent-b-ord.xx.fbcdn.net/hphotos-xap1/v/t1.0-9/10868213_10152451162981394_4080056179223702862_n.jpg?oh=e21db53eb831b7a175d9c3a5b070f1d5&oe=54FD9088
12. ### Throwing Knife Physics: Why Blade End Hits More Often

When a throwing knife is thrown why does it only hit its blade end ( not the grip end)? The knife has been imparted with a spin and there is a 50:50 probability that its blade end will hit (actually a bit less). It would be better if you explain assuming the blade's CM has velocity 'v' and is...
13. ### Diffraction Across a Knife Edge

I was having a discussion with someone far more expert than I and for whom I have a lot of respect. He was telling me that the path loss of a radio signal from A to B is not necessarily the same as it is from B to A. One of the reasons he mentioned is diffraction over a knife edge which in...
14. ### What force opens a folding knife?

If I flick open a folding knife with a flick of my wrist, what force is that? Is it centrifugal force, centripetal force, or some other force?
15. ### Forces on a wood-hacking machine knife

Please refer to attached figure and help to give a formula of how to calculate the force "F". This is a task from real-world, which means that there was a damage with this machine and now it is necessary to know the mentioned force. The information that is available to complete the calculation...
16. ### Sharpening knife edges, what is actually going on?

Hello folks, my study of physics is 20 years old or so please bear with me. I enjoy sharp knives and blades in general and am curious about what is actually happening when I sharpen them. I know these steels are a matrix composed of different elements tightly bound by nuclear forces, but I'm...
17. ### Exploring Art of Acid Etching Steel Knife Blades

hi , i am newbie here and reading through i find it ... stimulating.. now as to what brought me here.. i have wanted to look into art form of acid etching different knids of tempered steel used in stainless knife blades.. does anyone there know what mask coating will take a fine line...
18. ### Knife edge thickness/surface area

I'm having a hard time finding some documentation on the thickness of a knife edge. I need to calculate the force to slice an apple. I found the skin bursting strength to be 1.1 MPa. That means that assuming the thickness blade to be 10.0 micro-meters and the max length of contact with the...
19. ### Dead man wakes up under autopsy knife

"Dead" man wakes up under autopsy knife http://africa.reuters.com/odd/news/usnN1499758.html
20. ### Puppy Swallows 13-inch Knife - Lives With 8-Inch Scar

http://news.yahoo.com/news?tmpl=story&u=/ap/20050924/ap_on_fe_st/puppy_swallows_knife Six month old puppy swallowed 13-inch serrated knife. Lives with a 8 inch scar.
21. ### Exploring Knife Making & Steel Structure Changes

Hello, I just registered to these forums but already visited this place for a while. I have a question that fits this particular subforum (I hope). It is related to another hobby of mine, which is knife collecting/making. Let me give you first some background info on the subject, in order to...
22. ### What Are the Essential Physical Properties of a Stainless Steel Knife?

i need urgent help can anyone suggest some link that clearly states the physical property needed for a stainless steel knife? i desperately need it today. thz any help will be GREATLY appreciated
23. ### Can you throw a knife that doesnt even rotate or spin

Specially in the movies... i see people throw knives at enemy's neck or the head instantly killing them... some of the knife i saw.. fly straight without any rotations... how can you throw a knife that doesn't even rotate or spin... and travel straight with high velocity ? ( and the mass is...
24. ### Design details for a butter knife warmer

Hi everyone! I need help on how to build a butter knife that gets warm. I know I need to put a nichrome wire in the blade but would anything go at the end? Would I connect the wire to a battery? How do I find out what size battery to use and make it so the blade gets to a specific heat...
25. ### Cut a ball of mercury with a knife it forms into other balls

If I cut a ball of mercury with a knife it forms into other balls why is this