Card throwing

[insane_alien]

Okay, so i just watched the mythbuster episode with the killer deck myth. i know it can't actually kill people but i thought "hey that would be a cool thing to do" and since i only have two urgent things for uni i done some solid practice at it.

 

i must be doing something right because my plasterboard wall is covered in tiny cuts everywhere and my mum looks like she's going to rip my throat out via my nostrils.

 

through experimentation i know its all about spin and most of that comes from the wrist but how fast do these things have to be spinning to cut half a centimeter into plasterboard(drywall in the US i believe)?

[5614]

Well I'm guessing not that fast seeing as the guy on MythBusters could only throw his at 25mph, whilst that probably isn't a world record I would estimate you throw somewhere in that region.

 

So I guess what we'd like to know is why it is cutting so deep into the plasterboard.

 

Well the mechanical version on MythBusters threw the card at 155mph, this is a lot faster than you have any chance of throwing your card, however it only caused a small cut when the card was aimed at a human.

 

So we have:

155mph --> small cut on human

~25mph --> 5mm cut on plasterboard

 

I reckon the explanation of your 5mm cuts is more to do with the material (ie. plasterboard vs skin) and not that you can throw the card significantly quicker than 25mph.

 

I'm in the UK, but I know it isn't that hard to make a dent in the average internal house wall, just from occasionally throwing things, or hitting the wall whilst carrying a heavy object.

 

Two things to conclude with: firstly I can't really replicate this experiment at home due to technical difficulties (the air keeps stopping my card from reaching the wall at a decent speed!) and secondly 5mm is actually quite a deep scratch just from a card, is that an accurate value? And is this from just a standard playing card? And so is the cut about 0.5mm wide (roughly the width of a standard playing card)?

[insane_alien]

well, its a standard pack of cheap cards(plastic coated) and its roughly 5mm, when they went in it was at least 2 mm and i measured one at 6 although there is probably an error of ~ +/- 1 mm.

 

the depth seems to depend more on spin than lateral velocity as i got cards to stick in even if they are going way less than 25 mph.

[bored_teen]

guys, i just now joined this forum for the sole purpose of correcting you. but it looks...interesting. anyway...........

 

the reason the 155mph card did jack shit was because they didn't account for spin. a card flying at you spinning at 155mph would probably cut to the bone. spin, in essence turns a card into a flying buzzsaw. furthermore, you can kill someone with a card. but that requires accuracy, as well as power. you need to either cut through an artery/vein, or hit them at a pressure point.

[Bignose]

guys, i just now joined this forum for the sole purpose of correcting you. but it looks...interesting. anyway...........the reason the 155mph card did jack shit was because they didn't account for spin. a card flying at you spinning at 155mph would probably cut to the bone. spin, in essence turns a card into a flying buzzsaw. furthermore, you can kill someone with a card. but that requires accuracy, as well as power. you need to either cut through an artery/vein, or hit them at a pressure point.

 

Can you cite any scientificly determined proof for this (as this is a science board)? You really need to justify a statement like this with some sort of proof/evidence. Like, an order of magnitude calcuation or a video or something... For example, here are some order of magnitude calculations: For a "buzzsaw" I looked up "mitre saw" in google and used the first one I saw (I think it was on Home Depot's webpage).

 

It was a 12 inch saw which spun at 3800 rpm, and the saw blade was 2.8 lbs.

 

The moment of inertria for a spinning disk is [math]I = \frac{1}{2} m R^2[/math]

 

R = radius of the disk = 0.1524 m

m = mass = 1.27 kg

So, the moment of interia for a saw blade can be calculated as equal to 0.0147 kg m^2

 

Multiply the moment of inertia by the angular velocity and you get the angular momentum. The angular momentum is important since that is the momentum that will have to absorbed to stop the blade or card.

 

So, 3800 rpm times the perimeter of the blade means the blade spins at 3638 m/s. Mulitplying that all together, the angular momentum of a saw blade is 53.665 kg m^3/s

 

Now, let's look at a card spinning at 155 mph. The moment of inetria of a rectangle is [math]I = \frac{1}{12} m B H^3[/math] where H>=B (H is the longer side). Poker cards traditionally are 2 1/2 by 3 1/2 inches, and a deck of 52 cards weighs about 100 grams, so 1 card is about 2 grams.

 

So, calculating the moment of inertia of a card (and converting the untis to metric), I estimate

 

I_card = 7.4358 *10^-9 kg m^2

 

multiplying this by the edge speed of 155 mph (69.29 m.s) the angular momentum of a card can be found to be: 5.15 * 10^-7 kg m^3/s

 

Or, in other words, a saw blade has over 100 million times more angular momentum than a playing card spinning at 155 mph. I can confidently say that your statement "in essence

turns a card into a flying buzzsaw" is quite an exaggeration.

 

But, maybe you are right. That's why I'd like to see some objective proof, and not just take your word for it.

[kindadevil66]

jeez some ppl put way too much effort in small things the fact is a card spinning at 155mph has a much greater velocity and kenetic energy that a card traveling at 155mph so as bored teen says a card spinning could probably cut bone

no offence bignose i think your calculations are absolutly correct and all

[bored_teen]

i honestly don't know what you just said, Bignose. i'm 15 years old. i can honestly say that yes, it was an exaggeration. but did you take into account that a buzzsaw has many edges on the blade, while a card has only 4?

 

lemme rephrase my previous post. on Mythbusters, they made a device that shoots a card at 155 mph. but that device didn't take into account spin; the card didn't spin when it was shot, it flew straight. that makes it more of a slap than a cut. a spinning card will cut while a non-spinning card won't. i'm not sure why. i'm not sure why a lot of things work. my informal theory is that a spinning card will create friction on impact, cutting the skin. the same reason why you can touch a razor and not get cut unless you run your finger over the blade.

 

Bignose, i respect you for coming back at me with complex equations, but i'm not impressed that you lacked the sense to notice such an eccentric hyperbole. i don't really know where i'm going to find these sources. but i'm a bored teen, so maybe i'll stumble across something.

[Rocket Man]

if you have a disk or other cutting device, you can generally cut something softer than the disk material. paper cannot cut bone!

 

i can see where this guy is coming from;

since paper has a sort of grain, i'm thinking that a spin applies a slicing action to the subject, reducing the workload on a single portion of the card while also utilising the abrasive properties of cardboard. (paper cut)

 

an impact with the edge of a card basically dents it and flattens the edge increasing surface area and reducing working pressure.

 

the only problem with this theory is that mythbusters maximised both spin and velocity.

if you check any high speed of a flying card, only one edge impacts. multiple impacts will move the card out of the existing slot making the first and most effective utterly useless.

 

it's not about friction, or energy. it's about pressure and momentum. a diamond bur blade can cut bone and rock but is absolutely incapable of cutting skin and flesh.

on hard objects, only a few diamonds touch the compund at a time. they have a minimum working pressure.

skin increases the working area requiring far more pressure to do the cutting.

 

it's the same for a card. if you take the edge of a playing card under a microscope you'll find it looks similar to a bur blade. efficient at cutting hard objects and poor at cutting elastic ones. the momentum serves only to apply greater forces for more time.

[bored_teen]

one edge may only hit, but it only becomes a slap if it is stopped completely at the time of impact. if you can (no, i'm not making fun of you or suggesting you are unable; most people can't do it very well because they haven't done it before), throw a card at a wall. it bounces off, usually. it hasn't completely stopped. it continues to spin, which causes friction, which may/may not cause a cut/abrasion to the surface of the wall, depending on various factors.

[Bignose]

bored_teen. I understand that you have a theory. I disagree with your theory, and I went into detail to explain why I disagree. What I would like is some concrete objective evidence (again, like a video, or some order of magnitude calcuations) from you that supports your theory. If you have none, then we have to begin to seriously doubt the validity of your theory. Not to put too fine a point on it, but this is a science forum and this process of providing objective support for a theory is exactly how science works. So, can you provide any evidence?

[bored_teen]

i have yet to find any evidence online. so for now, all i have is my experience with throwing cards, and examples such as the knife one. but you already rebuked that one into submission. i have no calcuations, as i'm a sophomore in high school next term. i honestly don't know what your calculations meant, so technically i can only accept those equations as based on your word. but i'm okay with that. i will continue my search for evidence, attempt to come up with various scenarios involving the cutting of flesh due to various factors, and if all else fails, create some sort of experiment to dis/prove this. after all, it's called the scientific method. also, you didn't answer one of my previous questions, being did you account for the card having only 4 edges.

 

by the way, i'm a sarcastic person by nature, i'm sorry if it comes out that way. i in no way am making an attempt at sarcasm.

 

and Rocket Man, a card may be similar to a bur blade on the microscopic level, but microscopic edges only cause microscopic cuts.

[bored_teen]

i was just looking for evidence, and it just occurred to me that i'm not sure what it is that needs proving. i'll say it up front, this is not some gimmick to make you forget that i have no evidence. i'll be the first to tell you that. but after re-reading the posts, i'm not sure what it is i'm being asked to prove. that cards can cause cuts? that a card can be turned into a buzzsaw (which is different from a mitre saw, and it also needs to be said that that metaphor was an exaggeration)? or am i proving the reason cards cut skin is because of friction?

[Bignose]

a card flying at you spinning at 155mph would probably cut to the bone.

 

This specific sentence, right here, is what I'd like to see evidence of.

 

And, yes, I treated the card as just a rectangle. It was only a comparison between the angular momentum of a card (considering its mass, size, and speed) compared with a saw (and it's mass, size, and speed)

 

Actually, looking at that quote I quoted, I am curious why you consider spinning to be different from lateral movement? Either way, the edge is moving at 155 mph, the same speed means that the penetrative power is the same, and a card embedded in flesh would probably come to rest pretty quickly, so i don't think that the spinning isn't going to make a lot of difference anyway. I think that spinning would only change the way the card embeds in the flesh, not the depth it embeds.

 

As much as anything, the problem with your theory is that a card is only 2 grams of mass. Compare that with a poker card sized sheet of aluminum or lead -- much more mass and hence momentum & energy behind it. You have to get something very light moving very, very fast to have a lot of momentum and energy.

[bored_teen]

hmm point taken. and looking back at it, it is a rather far-fetched claim. cut bone maybe, but not necessarily cut to the bone. to cut to the bone, a card would have to penetrate the skin, then blood and muscle, to the bone. and a card cutting muscle tissue is unlikely. i retract that statement. Bignose, i concede.

 

i recently rewatched the Mythbusters episode, and the card did in fact spin. the last time i had viewed this episode was the original air date. to me at the time the card looked like it went straight. i don't know why. i won;t let this sort of situation reoccur.

[Rocket Man]

speaking of bones, i'd like to pick one too.

 

you can't cut bone with paper!

 

the only reason a burr blade works is because the burrs are harder than the object getting cut.

the only reason a hack saw works is because the teeth are harder than the object getting cut.

any cutting tool you can find, i guarantee the blade is harder than the object getting cut.

 

show me some experimental evidence that plastic coated cardboard, a very soft material can cut bone, a very hard material.

 

cutting plaster board is different to bone and flesh. there's not much pressure you can apply to it before it starts crushing. if i had a sample, i would drive a card into it removing velocity from the equation to demonstrate that card is infact harder than plaster board.

(and don't argue that plaster board is just brittle, "hardness" is measured by pressure)

[bored_teen]

i said maybe...

 

and that depends on the type of bone, the condition of the bone, etc. maybe it is a bone from a 2 year old, not fully formed and hardened. maybe it's the bone of a mosquito (do they even have bones?), which would be really small.

[bored_teen]

are we all in agreement that you can kill with a card by striking varios pressure pints, nerve clusters, etc.?

[insane_alien]

maybe if your in space and the card comes at you at a few kilometers per second.

 

other wise, a couple of shallow cuts is the best you can do.

[bored_teen]

yes, but it's not about cutting. a card coming at you at 25 mph will still cause impact, which is why they usually cause stinging welts. if you hit someone at a pressure point at 90 mph, they would probably die, right?

[insane_alien]

no. they wouldn't.

 

a card just doesn't have the mass or the strength. you'll draw blood sure but there'll be no serious damage.

[Rocket Man]

i'd be surprised if any animal had bone softer than cardboard at any stage of develpoment.

you can snap a mosquito's exoskeleton without th use of pressure, but that's not a cut, that's snapping under force. you can't cut any thing harder than paper with paper in just the same way as you can't fashion a tungsten carbide tip using mild steel

[foodchain]

I am sure if the card was traveling around 4000mph it could do some serious damage, but that’s besides the point and I don’t even know if the card would hold up to such speeds or stress. I have played around with throwing cards and such, and going from the concept of a paper cut, which is not to difficult to obtain if you do it just right the card might be able to cut on throwing strength of an "average" person, but giving the sort of blunted edges on most cards this probably makes such that more difficult.

[AceThrower]

Can you cite any scientificly determined proof for this (as this is a science board)? You really need to justify a statement like this with some sort of proof/evidence. Like, an order of magnitude calcuation or a video or something... For example, here are some order of magnitude calculations: For a "buzzsaw" I looked up "mitre saw" in google and used the first one I saw (I think it was on Home Depot's webpage).

 

It was a 12 inch saw which spun at 3800 rpm, and the saw blade was 2.8 lbs.

 

The moment of inertria for a spinning disk is [math]I = frac{1}{2} m R^2[/math]

 

R = radius of the disk = 0.1524 m

m = mass = 1.27 kg

So, the moment of interia for a saw blade can be calculated as equal to 0.0147 kg m^2

 

Multiply the moment of inertia by the angular velocity and you get the angular momentum. The angular momentum is important since that is the momentum that will have to absorbed to stop the blade or card.

 

So, 3800 rpm times the perimeter of the blade means the blade spins at 3638 m/s. Mulitplying that all together, the angular momentum of a saw blade is 53.665 kg m^3/s

 

Now, let's look at a card spinning at 155 mph. The moment of inetria of a rectangle is [math]I = frac{1}{12} m B H^3[/math] where H>=B (H is the longer side). Poker cards traditionally are 2 1/2 by 3 1/2 inches, and a deck of 52 cards weighs about 100 grams, so 1 card is about 2 grams.

 

So, calculating the moment of inertia of a card (and converting the untis to metric), I estimate

 

I_card = 7.4358 *10^-9 kg m^2

 

multiplying this by the edge speed of 155 mph (69.29 m.s) the angular momentum of a card can be found to be: 5.15 * 10^-7 kg m^3/s

 

Or, in other words, a saw blade has over 100 million times more angular momentum than a playing card spinning at 155 mph. I can confidently say that your statement "in essence

turns a card into a flying buzzsaw" is quite an exaggeration.

 

But, maybe you are right. That's why I'd like to see some objective proof, and not just take your word for it.

 

 

Speaking of the world record, it is the record for the fastest and longest throw of a standard playing card. The record is 216ft. 4in. thrown at 92mph by Rick Smith Jr. of Ohio (US). If you look him up or visit his website (RickSmithJr.com), you'll come to find he made an appearence on Time Warp (http://ricksmithjr.com/cleveland_magician.php?targetScript=media.rs.php). You can see, with the help of a high speed camera, Rick cutting through various articles of food in slow motion. One in particular, the carrot which is substantially denser and harder on the surface than human skin, is easily cut with one swift motion. Assuming his record is the fastest he can throw (92mph), if a card were to be thrown at 155mph (verticle speed) with the angular momentum and force on impact of the mimscule area acheived with Rick's technique, calling it a "flying buzzsaw" might not be so far off, given the right medium the card enters.

[Doc. Josh]

The card dosnt have enough density to penetrate the skin. The skin is ( flexible, Rubbery) per say and absorbs the impact force needed to penetrate. If in fact the card was denser heaver and flew true then it is plauseable. but a standard playing card being thrown from a human hand will do no more then a paper cut.