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Amount of kinetic energy reached..? (Read 8506 times)
Fëanor
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Amount of kinetic energy reached..?
Jun 10th, 2009 at 8:25am
 
Haven't made my first sling yet but I am getting on it today, was just wondering if any one here has measured kinetic energy or in practical terms the killing power of this weapon.
Saw a clip on youtube claiming 38 m/s with a 100-130 g stone which would translate to 72.2 joules at the low end.
What speeds are most of you experiencing at which weights?
Of course recording speeds are more arduous than range and weight and it still only gives the average speed which doesn't really equate to the actual amount of energy being transfered to the target but it would still be helpfull.
If someone here has access to equipment for measuring the actual hitting power that would of course be awesome but it seems unlikely.
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On the Swedish coast   With Russia in the distance Slinging at the bear. (4accord done it) "Mind must be firmer, heart the more fierce, courage the greater, as our strength diminishes."  The old warrior Byrhtwold during the battle of Maldon in 991 AD.
 
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Aussie
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Re: Amount of kinetic energy reached..?
Reply #1 - Jun 10th, 2009 at 10:07am
 
Greetings Feanor,

Welcome to the forum.

Very in depth question for a first post. Comes up quite regularly but is very difficult to answer because "killing power" is so open to interpretation. There is quite a detailed article by Dr Robert Dohrenwend which comes up with a "lethality index" (can't remember if that's its actual name) comparing various weapons, but there is quite a controversy over the way the data is interpreted. There is even controversy over whether the wound inflicted would invariably be only percussive orpenetrate into the flesh, though I think the evidence is fairly clear that leaden projectiles at least did actually penetrate the bodies of their victims.

However kinetic energy and momentum figures are easily calculated once weight and speed is known. But most of us are enthusiastic amateurs without access to sophisticated speed measuring equipment, so accurate speed measurement can be a bit of a problem. The easiest method of doing this I know using only readily available equipment is to record the sound of the sling,  using a laptop computer or similar, over an accurately measured distance. (I usually use 10m as I assume the speed doesn't drop too greatly over that distance and the sound interval between the swish of the release and the whack of the projectile hitting the target is quite perceptible.) Then examine the waveform of the recorded sound using Audacity or a similar program to accurately determine the time interval. The release usually produces a slightly fuzzy wave but the hit gives a very distinct spike which is easy to place on the time scale. Average velocity over the measured distance is then easily calculated.

From my own and others measurements as well as observing the many video clips of slinging on YouTube it appears that anything over 40 m/s, especially with so heavy a projectile is very good. Anything over 60 m/s would be excellent, over 100 m/s would be Larry Bray's record distance type speed. I don't know if his speed has ever been measured but his record of over 437 m was established with a stone of around 2 oz. You will find that personal preference for what consitutes the ideal weight varies a lot. Many throw 150 g or more whilst others use very light weights in the order of 20 g or even less. Tennis and golf balls are very popular ammunition weighing approx. 56g and 45g respectively.

Hope the above has been of assistance.

Regards,

Aussie
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Fëanor
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Re: Amount of kinetic energy reached..?
Reply #2 - Jun 10th, 2009 at 12:07pm
 
Thank you for your swift reply and the welcome. Smiley
That would be one of the best ways to measure velocity.
Will check out the source you've mentioned.
Did think about it after my post and reached the conclusion that some sort of ballistics clay would be best to measure the energy unleashed at the target.
Realised then that the most economic way to find out would be to send a lot of outlandish claims about slings generating massive amounts of kinetic energy equaling .50 cal rifles and such to the mythbusters.  Grin
Would maybe result in one or two of the more experienced ones from this forum living in the states would get to show of their skills on TV.
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On the Swedish coast   With Russia in the distance Slinging at the bear. (4accord done it) "Mind must be firmer, heart the more fierce, courage the greater, as our strength diminishes."  The old warrior Byrhtwold during the battle of Maldon in 991 AD.
 
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Rockman
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Re: Amount of kinetic energy reached..?
Reply #3 - Jun 10th, 2009 at 12:25pm
 
Measuring the kinetic energy of sling shots is very easy. All you need is to have it on tape to make your calculations.
Foe example, if you know your 100 gram projectile takes .15 secconds to reach the target at 10 meters 10/.15 equals 66.6 meters per seccond.
From there, you can obtain kinetic energy, I always use the link below.

http://www.csgnetwork.com/kineticenergycalc.html

Speaking of, sling shots can indeed have as much kinetic energy as some modern firearms, but this energy does not translate into deadliness. A bullet is more deadly because of their faster velocities and smaller size.
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Fëanor
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Re: Amount of kinetic energy reached..?
Reply #4 - Jun 10th, 2009 at 4:05pm
 
Yes, I understand how to calculate the average kinetic energy over the distance measured but since the energy drops it is at itīs lowest on impact, measuring the actual impact would tell most.

I do not doubt that slings can generate as much kinetic energy as some firearms but I am sure it would take some catapult or trebouchet construction to equal the .50 rifle rounds which according to wikipedia generates 15 000 - 20 000 joules compared to the example you give of 222 joules.

I would say that bullets are more deadly because of the type of damage smaller size and higher velocity does, I mean a joule is a joule whether it is generated by speed or mass.
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« Last Edit: Jun 10th, 2009 at 6:19pm by Fëanor »  

On the Swedish coast   With Russia in the distance Slinging at the bear. (4accord done it) "Mind must be firmer, heart the more fierce, courage the greater, as our strength diminishes."  The old warrior Byrhtwold during the battle of Maldon in 991 AD.
 
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Rockman
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Re: Amount of kinetic energy reached..?
Reply #5 - Jun 10th, 2009 at 4:17pm
 
Fëanor wrote on Jun 10th, 2009 at 4:05pm:
Yes, I understand how to calculate the average kinetic energy over the distance measured but since the energy drops the energy is at its lowest on impact, measuring the actual impact would tell most.

You're right, unfortunatley, such measurment would require an advanced equipment (to my knowledge, no member has such a device) so the average energy will have to do.

I would say that bullets are more deadly because of the type of damage smaller size and higher velocity does, I mean a joule is a joule whether it is generated by speed or mass.


It was explained to me by Aussie that kinetic energy the same in this two scenarios: A high caliber riffle bullet and a truck moving at 5 kph. They both have the same kinetic energy, but the bullet, with it's low mass and high speed kills and the truck's big mass and low speed would only push you to the side. No event is more powerful than the other, it's how you apply such energy that counts for killing power.
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Fëanor
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Re: Amount of kinetic energy reached..?
Reply #6 - Jun 10th, 2009 at 5:25pm
 
Yes, it would take advanced equipment or one could use clay and do some calculations.
I will get back to you all about my results when I have sufficient data.

I am not disputing that you can take the same amount of energy and take extreme ratios of mass and velocity, you could take a speck of dust and shoot it of in near light speed and not be hurt also or the mass of a glacier and die waiting to be hit. Smiley

What I was saying is that if you compare the two types of projectiles we are talking about with equal amounts of kinetic energy a modern bullet would be deadlier because of the type of damage.
Deep penetration most likely resulting in massive blood loss can kill you over time and with losing large amounts of blood you also run a high risk of deadly shock.
That is not as likely with concussive damage, as Aussie said in the case of glans you do have some penetration so there can of course be bleeding or breaking a bone and that causes bleeding but it is not as big a factor as in the deep penetrative damage of a bullet.
Both types of damage can damage internal organs but seems more likely in the bullet scenario.
If we are talking about high velocity rifles or hollow point bullets you also have to deal with lots of dead tissue in the body and with all bullets ruptured intestines and pieces of clothing in the wound, all three will cause sepsis if left without medical attention.

So all I was saying is that penetration damage is in my estimation worse than concussive damage, of course concussive damage can kill but as I see it there are more complications dealing with penetrative damage.

The reason why I am saying it is because your statement about a bullet being deadlier because of it's smaller size and higher velocity is not true but itīs mincing words so lets drop it.
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« Last Edit: Jun 10th, 2009 at 6:53pm by Fëanor »  

On the Swedish coast   With Russia in the distance Slinging at the bear. (4accord done it) "Mind must be firmer, heart the more fierce, courage the greater, as our strength diminishes."  The old warrior Byrhtwold during the battle of Maldon in 991 AD.
 
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Rockman
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Re: Amount of kinetic energy reached..?
Reply #7 - Jun 10th, 2009 at 7:37pm
 
What we need is some kind of test. Me and my friends are trying to decide what to use for simulated flesh and we have a strong candidate, one type of squash. I have seen it, touched it and It's very close to the density of flesh. The other choice is a watermelon, but we're about to discard that idea, the squash is more consistent.

The only time there's been a test of a sling shot to a head replica was on that show Deadliest Warrior, they fired a glande and it got stuck inside the skull. David's shot at Goiliath was done with a rock, it would be intresting to see the same test with the rock, to see what happens.

Firing lead glandes and rocks at the body is something that should be tested on a side of pork, like they do with archery or atlatls. you can't beat the realism of such test.

And yes, I understand why bullets kill. Apparently, when you list the ways to efficiently kill a human, penetration of the organs is among the best. The very fast velocity  and penetration of the bullet destroys internal organs. 

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Re: Amount of kinetic energy reached..?
Reply #8 - Jun 10th, 2009 at 7:42pm
 
As you can see there are quite a few differences of opinion. Dohrenwend emphasizes momentum over energy as being the dominant factor in "lethality" and this favours the heavier, slower moving projectile as KE varies as the square of speed.

There are a quite a few doubtful claims made about sling stones having the same energy as high power rifles etc. Fairly over the top really. Ultimately the energy comes from the slinger's arm, not the sling. Just how much energy can any slinger transfer in the short time he does work on the stone during the slinging action? Let's assume a very generous power output of 1000 W. Let's also assume a generous 0.25 sec during which the stone is being accelerated. Even with 100% efficiency this implies a max. energy of 250 J. Of course even this would be exceptional.
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« Last Edit: Jun 11th, 2009 at 4:37am by Aussie »  

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Mr. Boss
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Re: Amount of kinetic energy reached..?
Reply #9 - Jun 10th, 2009 at 11:34pm
 
Rockman wrote on Jun 10th, 2009 at 7:37pm:
What we need is some kind of test. Me and my friends are trying to decide what to use for simulated flesh and we have a strong candidate, one type of squash. I have seen it, touched it and It's very close to the density of flesh. The other choice is a watermelon, but we're about to discard that idea, the squash is more consistent.

The only time there's been a test of a sling shot to a head replica was on that show Deadliest Warrior, they fired a glande and it got stuck inside the skull. David's shot at Goiliath was done with a rock, it would be intresting to see the same test with the rock, to see what happens.

Firing lead glandes and rocks at the body is something that should be tested on a side of pork, like they do with archery or atlatls. you can't beat the realism of such test.

And yes, I understand why bullets kill. Apparently, when you list the ways to efficiently kill a human, penetration of the organs is among the best. The very fast velocity  and penetration of the bullet destroys internal organs.  

 


On deadliest warrior they slung what looks to be 5-7 ounces of lead at 91 mph, if you doubled (or almost tripled) the speed and used a 4 oz rock, then it would most likely be way more penetration.
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Re: Amount of kinetic energy reached..?
Reply #10 - Jun 11th, 2009 at 4:53am
 
Mate, of course it would. Trouble is you'd have to be Hercules on steroids to do it.
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Fëanor
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Re: Amount of kinetic energy reached..?
Reply #11 - Jun 11th, 2009 at 6:52am
 
But the denser material lead would still be best for penetration, 4 oz lead ball or, to take extremes, 4 oz depleted uranium ball would be even better with the doubled or tripled velocity mentioned.
Ballistics is difficult enough so with the added difficulty of having it affect a body with large variations depending on where you hit it seems to make it a lot easier to rely on empirical data.
Easiest would be to use live pigs and just see if the hit kills it but I am not tempted, dead pigs adds the difficulty of assesing if the hit would kill in cases of torso hits.
How do internal organīs properties change in death?
Reason i pose the question is would say a hit on the spleen that is sufficient to rupture it on a live animal through blunt force also rupture it on a dead animal? Or damage a liver etc.
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On the Swedish coast   With Russia in the distance Slinging at the bear. (4accord done it) "Mind must be firmer, heart the more fierce, courage the greater, as our strength diminishes."  The old warrior Byrhtwold during the battle of Maldon in 991 AD.
 
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Re: Amount of kinetic energy reached..?
Reply #12 - Jun 11th, 2009 at 9:05am
 
My, this discussion is getting cheerful. Just out of curiosity is there any particular reason you want to know how much force is required to rupture a dead pig's spleen? Please let us know how your depleted uranium experiments go, local scrap metal dealer didn't have any last time I asked.
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Re: Amount of kinetic energy reached..?
Reply #13 - Jun 11th, 2009 at 10:42am
 
Feanor, have you made a "first sling" yet?

If so, what kind did you decide on?
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Rockman
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Re: Amount of kinetic energy reached..?
Reply #14 - Jun 11th, 2009 at 2:14pm
 
If the corpse is fresh, then it shouldn't be a drastic difference, only if the body was too decomposed.
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