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Nathan Gilleland





Joined: 25 Apr 2008

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PostPosted: Thu 18 Jun, 2009 10:04 am    Post subject: watermelon vs. head density         Reply with quote

I was watching a murder mystery/ forensics science show recently, and in the show, they state that a watermelon is the same density as a human head. Eek! This intrigued me, and so I did some online researching, but wasn't able to locate a reputable source to confirm this claim. Worried

My question is this:

Does anyone know whether a watermelon is accurately comparable to a human head in terms of density and cutting medium?

(Morbid, I know, but it intrigued me) Eek!

If you could post a source that backs up posted information, it would be greatly appreciated. Happy

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Allen Jones




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PostPosted: Thu 18 Jun, 2009 10:29 am    Post subject:         Reply with quote

I don't know for sure but I would say no. I have always heard that a coconut is as hard as the human skull. If that is true than the watermelon wouldn't be good for testing blunt force trauma. The truth of the matter is that there are lots of quality products that simulate bone and tissue that a forensic scientist would use before fruit. I don't know what they were doing but the plus for using a watermelon on TV is that is roughly shaped like a human head, cheap and easy to find (in season) and full of red stuff.
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Martin Murd




Location: Pärnu, Estonia
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PostPosted: Thu 18 Jun, 2009 11:10 am    Post subject:         Reply with quote

Watermelon: Shell is softer than skull and interior does not remind brain tissue in any way. At least, when it is ripe. Not much use for cutting exercises as well (You can cut watermelon in half with piece of rebar, without much trouble).

But it looks good on forensic shows and dinner table Happy

Merlon
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Steaphen Fick





Joined: 01 Jan 2007

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PostPosted: Thu 18 Jun, 2009 11:25 am    Post subject: inside ballistic gel         Reply with quote

I want to put together some ballistic gel targets, but I'd like to put in some bone substitutes. Does anyone know what I could use for the skull, ribs and arms?

I really don't want to use the plastic skeletons, as I don't think that would be as accurate as it could be.

Thanks everyone.
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Dan P




Location: Massachusetts, USA
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PostPosted: Thu 18 Jun, 2009 11:26 am    Post subject:         Reply with quote

Strictly speaking in terms of DENSITY I'd guess they'd be pretty close overall- since both a head and a watermelon are mostly water.

In terms of structural strength, cutting resistance... much different. But a better question might be "what level of blunt trauma or cutting impact would it take to render the structural differences between a head and watermelon irrelevant when determining the final result" Eek!
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David E. Farrell




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PostPosted: Thu 18 Jun, 2009 1:43 pm    Post subject: Re: inside ballistic gel         Reply with quote

Steaphen Fick wrote:
I want to put together some ballistic gel targets, but I'd like to put in some bone substitutes. Does anyone know what I could use for the skull, ribs and arms?

I really don't want to use the plastic skeletons, as I don't think that would be as accurate as it could be.

Thanks everyone.


go to a butcher and get some bones. Sometimes you can get lucky, though it would be pretty nasty to work with. But if you are trying to make something human shaped, that won't work so great.

I once heard from a friend that worked testing fans that they had to use wet bones (usually chicken leg bones to simulate finger bones) in some tests, as clean, dry bones were often more brittle.

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Douglas S





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PostPosted: Thu 18 Jun, 2009 3:15 pm    Post subject:         Reply with quote

One thing's for certain, and well-known to medical science: dry (dead) bone is more brittle that live bone. It may appear stronger in some ways, but will shatter more easily.

Steaphen, there are studies that have been run by the military on traumatic wounds. I wouldn't know where to go searching for it, though.
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Addison C. de Lisle




Location: South Carolina
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PostPosted: Thu 18 Jun, 2009 6:55 pm    Post subject: Re: inside ballistic gel         Reply with quote

Steaphen Fick wrote:
I want to put together some ballistic gel targets, but I'd like to put in some bone substitutes. Does anyone know what I could use for the skull, ribs and arms?

I really don't want to use the plastic skeletons, as I don't think that would be as accurate as it could be.

Thanks everyone.


I'm pretty sure that this question has been asked before, and Peter Johnsson recommended using PVC piping as bones. I believe that wet newspaper was also suggested as a simulation of meat. Hope this helps.

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Michael B.
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PostPosted: Thu 18 Jun, 2009 8:35 pm    Post subject:         Reply with quote

So, this sparked my interest so I ran down to the gorcery store and bought a coconut. After going through a couple noodles and 15 waterfilled bottles, I put the coconut on the stand....
Yeah, not easy. In fact, I took off the top of the cocout and sent it flying, but for the life of me I was having a hard time cutting the rest of it. If that's not close to bone, I'll be surprised.

Note: I was using an Albion Tolhoffer with a good edge.

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Michael Bergstrom
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Alan Schiff
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PostPosted: Thu 18 Jun, 2009 10:07 pm    Post subject:         Reply with quote

I've cut watermelons before and they are definitely not a good substitute for skulls. It takes almost no effort at all to slice one completely in half with an axe or sword, even if it's not very sharp. I don't know about coconuts.

As far as bones go, when the Mythbusters were re-making their test dummy Buster, they did several tests on different human bones and several substitute media and figured out that poplar dowels and squares have similar breaking and stress-handling characteristics to bone. I seem to remember that a 3/4 inch poplar square was equivalent to a human femur in their tests. I don't remember what they used to simulate the skull.

You might want to check out their website and see if they have those results, and if not you could perhaps email them, or I know that there is a forum there somewhere as well.

Hope this helps,
Alan
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Nat Lamb




Location: Melbourne, Australia
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PostPosted: Fri 19 Jun, 2009 7:13 am    Post subject:         Reply with quote

Watermelon also much more susceptable to fists. I can quite happily punch a hole in a watermelon, but I have never seen a fist get stuck in someone's head in a fistfight.
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J. Scott Moore





Joined: 25 Nov 2008

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PostPosted: Fri 19 Jun, 2009 12:59 pm    Post subject:         Reply with quote

Nat Lamb wrote:
Watermelon also much more susceptable to fists. I can quite happily punch a hole in a watermelon, but I have never seen a fist get stuck in someone's head in a fistfight.


Not without a blade attatched to said fist, anyway. like a katar. or other like weapons...

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M. Eversberg II




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PostPosted: Fri 19 Jun, 2009 5:59 pm    Post subject:         Reply with quote

It's also decidedly more delicious than head.

M.

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Sam Gordon Campbell




Location: Australia.
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PostPosted: Sat 20 Jun, 2009 12:58 am    Post subject:         Reply with quote

M. Eversberg II wrote:
It's also decidedly more delicious than head.

M.


Eek! I lol'd Laughing Out Loud

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Peter Johnsson
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PostPosted: Sat 20 Jun, 2009 12:55 pm    Post subject: Re: inside ballistic gel         Reply with quote

Addison C. de Lisle wrote:
Steaphen Fick wrote:
I want to put together some ballistic gel targets, but I'd like to put in some bone substitutes. Does anyone know what I could use for the skull, ribs and arms?

I really don't want to use the plastic skeletons, as I don't think that would be as accurate as it could be.

Thanks everyone.


I'm pretty sure that this question has been asked before, and Peter Johnsson recommended using PVC piping as bones. I believe that wet newspaper was also suggested as a simulation of meat. Hope this helps.


Hi,

I do not think PVC pipe is a good substitute for bone. It is much too brittle.

In a thread ages ago, the same, or similar questions were discussed. At that time I said:

-----------
Something I find seful as a target is wet newspaper rolled up.

I use a plastic pipe as a core. It is of a type marketed as Fusiotherm, used for plumbing instead of copper pipe. It has especially good characteristics fro test cutting as it pretty similar to living bone. It is hard buyt still tough. Hacking through it with an axetakes some effort and time. A good clean hit with a sword will sever it, however. You can get it in different diameters.

http://www.fusiotherm.com/306.0.html
http://www.fusiotherm.com/?id=333

At around 15 mm diameter is useful in pairs taped together with duct tape (=lower arm?).
At around 25-25 mm diameter is useful to mimic upper arms and leg targets.
At around 30 mm you get something like upper thigh or spine/neck.

25-30 milimeter is demanding for a single hand sword. 15 mm is easy.

Around this I wrap thoroughly soaked newspaper (back fold cut away to remove staples: it also helps getting the pages thoroughyl soaked). Put a pile of pages into a tub and fill with water. Let sit for a little while and makesure the water has reached all surfaces. Do not let the paper soak for too long as it will turn into a pulp.

When wrapping around the plastic pipes I apply enough pressure to squeze out most of the water, but not so much it becomes completely compact.
This material feels very similar to a sharp edge as raw meat. It is wet and fibrous, providing both resistance and lubrication. The mass (density and weight) is about the same as well.

I seal this with a layer of duct tape. This helps keeping the paper in place and also comes close to skin.

A telling target, it is a bit morbid. By using different diameters of pipe and varying the amount of paper wrapped around it, you can get targets of different difficulty.
I cannot guarantee the correspondense is absolute to a living target of same size and mass, but it is pretty close.
-------------------

The thread is here:
http://www.myArmoury.com/talk/viewtopic.php?t=9239

Ballistic gel would not be a good target to simulate flesh. Gel will probable cause drag, while wet newspaper is self lubricating in the same way as raw meat.
Wet newspaper will work well in this regard.It is both fibrous, offers some resistance and is also self lubricating.
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Addison C. de Lisle




Location: South Carolina
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PostPosted: Sat 20 Jun, 2009 3:22 pm    Post subject:         Reply with quote

Very sorry to misquote you Peter; I remembered wrong and couldn't find the thread. Thanks for correcting my mistake!
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Michael B.
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PostPosted: Sat 20 Jun, 2009 3:56 pm    Post subject:         Reply with quote

A new project! Thanks for the description! Yes, it's a bit of a morbid subject, but it's also relevant when it comes to the martial aspect of studying sword fighting.
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Michael Bergstrom
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Timo Nieminen




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PostPosted: Sat 20 Jun, 2009 7:52 pm    Post subject: Re: watermelon vs. head density         Reply with quote

Nathan Gilleland wrote:
I was watching a murder mystery/ forensics science show recently, and in the show, they state that a watermelon is the same density as a human head. Eek! This intrigued me, and so I did some online researching, but wasn't able to locate a reputable source to confirm this claim. Worried

My question is this:

Does anyone know whether a watermelon is accurately comparable to a human head in terms of density and cutting medium?


A human head - and most any part of the human body - is mostly water. A watermelon is mostly water. Both have - in the most common technical usage of "density" (i.e., mass/volume) - about the same density. If this is the intended usage in the show, it's accurate.

Not a similar cutting target, though, since resistance to cutting depends on much more than just density. (Just consider: a bucketful of water has about the same density as well, and water can be cut rather easily.)
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Chris Artman




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PostPosted: Sat 20 Jun, 2009 8:07 pm    Post subject:         Reply with quote

Bone is NOT mostly water, therefore your argument is invalid. The density of bone, also measured by xray attenuation is approximately 500 Houndsfield units avg wtih the cortex being even more dense. The brain is similar to watermelon, not the head which includes the skull. For reference the Houndsfield scale is a quantitative measure of radiodensity water has an attenuation of 0 Hounsfield units (HU) while air is -1000 HU and metal is about +1000 HU.

Its all about the skull...
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Michael B.
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Location: Chugiak, AK
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PostPosted: Sat 20 Jun, 2009 8:58 pm    Post subject:         Reply with quote

Chris Artman wrote:
Bone is NOT mostly water, therefore your argument is invalid. The density of bone, also measured by xray attenuation is approximately 500 Houndsfield units avg wtih the cortex being even more dense. The brain is similar to watermelon, not the head which includes the skull. For reference the Houndsfield scale is a quantitative measure of radiodensity water has an attenuation of 0 Hounsfield units (HU) while air is -1000 HU and metal is about +1000 HU.

Its all about the skull...


ZOOM!!!! Right over my head....errr skull. Except that bone isn't mostly water, I got that part.

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Michael Bergstrom
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