Welcome, Guest. Please Login
SLINGING.ORG
 
Home Help Search Login


Pages: 1 2 3 4 5 
Send Topic Print
The physics of the sling (Read 34841 times)
Matthias
Past Moderator
*
Offline



Posts: 1418
Gatineau/Ottawa QC, Canada
Gender: male
Re: The physics of the sling
Reply #30 - Aug 24th, 2004 at 12:29pm
 
Yes, I've gone quiet - Smiley I'm following along... and doing some background work. Almost have a high speed strobe and photo/acoustic-trigger built! I'm hoping to be able to provide some classic "lead-glans-penetrating-pumpkin" shots for the gallery. Should be able to get nice attitude-on-impact shots as well (provided I can hit the target). Projectile shape is slow due to a lack of either tools or slinging space depending on where I am. I'm away until the 2nd, but might be able to convince my "almost as crazy as me" family to assist in some sling performance evaluation while I'm visiting. Northern Alberta (prairie) is good sling country. Might finally be able to recover some projectiles!

And what about our "ball series" experiments? Surely some of you guys have some tennis/golf/base/softballs?

Hey and didn't we have some stop-motion pictures promised? David_T mentioned them a while back.

Matthias
Back to top
 
 
IP Logged
 
Thomas
Ex Member
****


Rocks?

Gender: male
Re: The physics of the sling
Reply #31 - Aug 28th, 2004 at 9:28am
 
I once made a simple device for measuring slinging force. It was a retention cord only, with a captive softball.Between the cord and  ball insert a short length of bungee. A piece of string is then used to remember the bungee stretch. Attach the string at one end of bungee and the other end across the bungee held fast by a rubber band. In use this assembly is whirled around to achieve the desired rate. The string has been drawn through the rubber band grip and will remember how far it was pulled. A weigh scale can be used to recover the force. I got approximately 20 pounds from the softball experiment. Of course this spinning achieved less than 70 mph! A recent post by Matthias dealing with a ballistic pendulum described a similar indicator idea. Someone could develop this into a real sling  and get reliable speed and force data. I don’t want to infer that elastic cords should be used in functioning slings.

Thomas
Back to top
« Last Edit: Nov 17th, 2004 at 12:26am by Thomas »  
 
IP Logged
 
Hondero
Senior Member
****
Offline



Posts: 463
Madrid-SPAIN
Gender: male
Re: The physics of the sling
Reply #32 - Aug 30th, 2004 at 12:56pm
 
ROUGH PROJECTILES

Although it´s somewhat incredible, the rugosity of the projectile has to do with the range, in the way of the golf balls, extending the reach, although not as much as in them because golf balls have less density and are affected in greater measure by this effect. Let us consider first a stone spherical projectile.

Re = Air density * Velocity * Diameter/air viscosity

Considering always the same projectile  Re= K1 * V

On the other hand :

Drag force Fd = Cd/2 *  air density * cross section * V^2  (CD = drag coefficient)

For the same projectile: Fd = K2 * CD * V^2

The drag force will vary then with the speed of the projectile, first by itself and secondly by its dependency of CD that varies with Re, that varies as well with V. The relation of CD with Re comes given from experimental form by the curves of Achenbach for spheres:

...

The upper curve, corresponding to smooth spheres, has an almost constant value around 0,5  until arriving at the point in which the speed of the projectile causes a turbulent air flow, falling drastically the CD. Nevertheless, the required speed for this it is higer than the maximum one that can reach a slinger, reason why hardly we will enter this favorable zone.

Nevertheless, if the sphere is rough, we see that the corresponding curve provides lower values of CD, now in the margin of speeds of the slinger. For that reason the air drag force will be smaller and greater the range. The curve shown corresponds to a projectile of rugosity K/D = 0,01250, wich expresses the ratio between the depth of the holes and the diameter of the projectile. Thus, for a projectile diameter of 4 cm the holes would be of 0,5 mm. A projectile like this is easy to make striking a smooth-stone around all their surface with another stone, or with a rounded hammer.

In order to calculate the increase of range of this rough projectil vs a smooth or polished one we will have to make approximated calculations, since the speed of the projectile will be changing as it goes being restrained by the air, and therefore will be changing its CD. In the picture I have selected two zones that corresponds to the variation of speed for projectiles thrown with two initial speeds: 55,55 and 120 m/s, that are the speeds of launching of the considered average slinger and of a recordman.
I have used the Simulator to get in both cases an aproach to the end speed of the projectile, that could be of about 25 m/s and 65 m/s respectively. As it is  very awkward to evaluate the effect of the changing Cd, I have taken an average Cd for each zone, as it is indicated in the figure. For a projectile of 100 gr. the calculated values of the range are:

Speed.......................55,55...........120 m/s
CD (Smooth) ........... 0,5............... 0,47
CD (rough)............... 0,272............0.37
Range (smooth )......167............... 353 ms
Range (rough )........ 208............... 409

We see that for the average slinger the increase of range with rough projectile is of 25%. The recordman, nevertheless, is penalized by the high end speed of the projectile, that does not take advantage of the zone of lower Cd.

The following calcualtions will be with lead projectiles, that surely also are influenced by this rugosity effect  (I progress little by little, but soon I´ll discover the carefully kept secret of Jurek... but I shall not disclose it  Wink )
Back to top
 

He brought a conquering sword..., a shield..., a spear... , a sling from which no erring shot was discharged.&&
WWW  
IP Logged
 
Hondero
Senior Member
****
Offline



Posts: 463
Madrid-SPAIN
Gender: male
Re: The physics of the sling
Reply #33 - Aug 31st, 2004 at 1:43pm
 
Before analyzing the rough lead projectiles, I want to show the Achenbach full graph, that includes a serie of curves corresponding to different rugosity, as it is seen in the figure. The curves can really be interpolated in a continuous way until arriving at the corresponding one to the perfectly smooth sphere.

...

We see as in each one of them the zone of minimum CD corresponds more and more at high speeds. Thus, our recordman of previous post, that had been underprivileged front to average slinger when using a projectile of rugosity 0.01250, does not have to do anything more than to use another projectile of smaller rugosity, like the one of 0.00150 to be able to get an average CD of 0.2, still smaller than the one of the average slinger, and to obtain therefore an increase of range with respect to the smooth projectile of 64%.

These so low values of the CD give rise to spectacular ranges, and make us to believe more and more in the possibilities of the sling if suitable projectiles are used. Each slinger has to choose the rugosity degree adapted to his power to get the best aerodynamic performances of the projectile. The suitable selection of the projectile plays then a decisive rol in the range, more than the simple power, and makes us imaging the high sophistication that could have the modern sling competition. After all, the sling, looking so simple, keep secrets that makes it a sophisticated weapon.

But coming back to the subject of the rugosity, we have seen that for a powerful slinger the optimal degree is quite small, and possibly a natural heavy grain stone without polishing, like the granite, provides the suitable value of rugosity. What we´ll have to avoid is the use of polished or very smooth projectiles.
Another observation is that it is not imperative for the slinger  to be a burly guy, and that a normal slinger, using a suitable projectile, can get excellent ranges.

Back to top
« Last Edit: Sep 1st, 2004 at 11:44am by Hondero »  

He brought a conquering sword..., a shield..., a spear... , a sling from which no erring shot was discharged.&&
WWW  
IP Logged
 
Yurek
Funditor
Past Moderator
****
Offline


The best thing, is a good
sling.

Posts: 942
Poland
Gender: male
Re: The physics of the sling
Reply #34 - Sep 2nd, 2004 at 3:03pm
 
Quote:
but soon I´ll discover the carefully kept secret of Jurek... but I shall not disclose it


Hondero,

Ohh no! It isn't truth. I have just tried to share it all time. But maybe... a bit clumsily Grin

After your last lecture, I should try dimpled glandes again.

Jurek

Back to top
 

In the shape, structure and position of each stone, there is recorded a small piece of history. So, slinging them, we add a bit of our history to them.
 
IP Logged
 
Hondero
Senior Member
****
Offline



Posts: 463
Madrid-SPAIN
Gender: male
Re: The physics of the sling
Reply #35 - Sep 5th, 2004 at 3:32am
 
ROUGH LEAD PROJECTILES

Let´s go on a little with this "saga" on projectiles that is almost arriving at the end. First I must say that the recordman considered until now, able to throw a projectile of 100 grams to 120 m/s seems at present some excessive, although it has helped us to get right percentage relations. The present real data of sling and baseball records indicates an approximate maximum power equivalent to the launching of 55 grams at 110 Km/h with a sling of 105 cm. This power match with a 100 gr. projectile thrown at about 105 m/s. Nevertheless we will continue considering this ideal recordman of the 120 m/s to make comparisons with the calculations made until now, although the ranges that we are going to see will surprise us a little.

I´ve used the same Achenbach curves that we saw for the stone projectiles, the one of 0,01250 rugosity for the average slinger and the one of 0,00150 for the recorman. Now the end speeds in both cases are greater since the lead projectiles has more dynamic inertia. These speeds are 40 and 90 m/s respectively, and the values corresponding to the average CD are 0,23 and 0.14.

Let us see the results in tables to not repeat the graphs:

Initial speed....................55.55.............120 m/s
End speed.........................40...................90 m/s
Average CD (smooth)......... 0,5.................. 0.5
Average CD (rough)............0.23................ 0,14
Range (smooth)................ 229................. 590 ms
Range (rough)................... 267.................990 ms

The increases in range for both slingers using the rough projectile are 17 % and 67 %. We see that the lead projectiles, that are smaller than those of stone (R.stone/R.lead = 1.6), accuse also widely the effect of the rugosity, contrarily whith what could be thought (I´m the first one surprised  Shocked)

Back to top
« Last Edit: Sep 5th, 2004 at 4:43am by Hondero »  

He brought a conquering sword..., a shield..., a spear... , a sling from which no erring shot was discharged.&&
WWW  
IP Logged
 
Hondero
Senior Member
****
Offline



Posts: 463
Madrid-SPAIN
Gender: male
Re: The physics of the sling
Reply #36 - Sep 8th, 2004 at 8:11am
 
GLANDES

Let us consider finally the famous effect of the shape and performances of glandes. The more trustworthy data on drag coefficients I´ve found are from H. Rouse (1946), and come expressed in the following curve:


...


The ellipsoid of the curve has a ratio between axes smaller than the typical glandes, whose average ratio could be 1:2.4, been the most fat of them about 1:2. Also the glandes have the ends more pointed and are more aerodynamic, reason why the values calculated here would be the minimal corresponding to a glans.

I consider again the two slingers of reference and their 100 gr projectile.  We obtain the following values:

Initial speed......... 55.55......... 120 m/s
CD......................... 0,1.............0.06
Range.................... 300............1280 ms

The increases of range in relation to spherical smooth projectiles are 31 y 116 % respectively. We remember that the speed of 120 m/s of our recordman is a little excessive, reason why the probable reach (for 105 m/s) would be of 1010 m. Also we have to not forget that this range is for a perfect orientacion point-first of the projectile, what will not happen exactly in practice although we use special throwing tecniques. In regard to the effect of rugosity I have not found any data, but given their aerodynamic shape, the rugosity could not play an important role, since the trail left by the glans is enough narrow and it would not be reduced as much as for the spherical projectile.

And since we are speaking of glandes we can consider also the glandes of stone that have been used in different times and places, and the clay glandes too that comes from the warlike origin of the sling (Neolithic). The values of Cd are the same that for lead glandes and we considere also the same projectile weight of 100 g. and the two speeds of reference.

Speed...........55.55 m/s.............. 120 m/s
Stone............ 277 ms..................1072 ms
Clay...............267 ms.................. 997 ms

Surprising! There is no excessive difference between glandes of lead, stone or clay!

Arrived at this point it is the moment for summarizing and put together in a table the results of the different calculations made with projectiles of different density, rugosity and shape. The data are corrected for a max. initial speed of 105 m/s.



RANGES WITH PROJECTILE OF 100 GR.
ACCORDING TO DENSITY, RUGOSITY and SHAPE


Initial speed(m/s) ..................55.55..........105
Spherical smooth stone.................167.............319
Spherical rough stone...................208.............508
Spherical smooth lead...................229.............516
Spherical rough lead.....................267.............818
Elliptical lead (1:1.8 ) ..................300.............1010
Elliptical stone (1:1.8 ) ................277..............875
Elliptical clay (1:1.8 ) ..................267..............821


One first conclusion is the great importance of the characteristics of the projectile, that can triple the range for the same weight and are so  important as the power of the slinger.

Another observation is that glandes have an extraordinary performance, been their shape more important than the projectil density.

And a last one, among the many that can be done calculating ratios between the different modalities of projectile, is that the rough spherical lead projectiles can compete with glandes if these are thrown not well oriented point-first.

This takes us to the study of the throwing techniques and to the Yurek´s graphs to study the more suitable position. But that will be another day, after a rest of at least one month or so Cheesy, when the secret to get the possible new Guiness record with lead (around 1000 m) will be eventually revealed  Grin.
Back to top
 

He brought a conquering sword..., a shield..., a spear... , a sling from which no erring shot was discharged.&&
WWW  
IP Logged
 
JohnHorn
Tiro
**
Offline


I love YaBB 1G - SP1!

Posts: 21
Re: The physics of the sling
Reply #37 - Jan 5th, 2005 at 5:09am
 
Excellent in-depth writings you guys have here. Some of it goes over my head, though some of it I understand. Smiley

Now my question:
What is the likely and unlikely exit-velocities of a Balearic slinger with a 1-mina stone (436 gram) - also one must take into account that these are not regular people that have never slung before, they have probably slung so much to the extent that their arms have become especially adapted to it, as well as strong for the purpose. Even so, I don't expect a Balearic slinger to sling a 436 gram smooth stone with 100 m/sec. Wink

Also, what would the likely range be for a Balearic slinger?
I'm working on a realism modification for Rome:Total War. And we need to know what characteristics should apply.

I know Balearic slingers slung more for accuracy, and less for range as they used stones from the beginning, while the Rhodian slingers slung more for range using their lead glandes. Also, at what point in history did the Balearic slingers start using lead bullets? I know that Diodorus says they used 436 gram big stones in 311 BC.


Basically, I would just like to know the ranges for Rhodian lead slingers and 436g Balearic slingers respectively. Based on your experiences and guesswork of course. Smiley

Leshatt na'imot!
That's "for a good year" in Hannibal's own language
Back to top
 
 
IP Logged
 
Paul Bardunias
Guest


Re: The physics of the sling
Reply #38 - Mar 28th, 2005 at 4:40pm
 
Let me commend all of you on this site- very informative. 

I have a question that you might be able to answer.  Doesn't a Glans shaped projectile need to spin in a fashion akin to a rifle projectile in order to fly true?  If it is not spinning along its long axis, the shape seems to ensure that it will spin along its short axis and the same force that aids in rifling would now cause it to veer- assuming a symmetrically weighted glans.

I'm not sure how the spin would be imparted, but if it exists it probably has to do withthe release from the pouch.  Are the pouches on ancient slings different for "bullets" than for balls?

Thanks,

Paul
Back to top
 
 
IP Logged
 
Zwiebeltuete
Descens
***
Offline


Fly! Angel, fly!

Posts: 143
Germany, near Nuremberg
Gender: male
Re: The physics of the sling
Reply #39 - Sep 23rd, 2005 at 8:38am
 
I began last year playing Golf and I noticed that it is not just the swing but many very important additional moves which makes the ball fly far. One very important move is the turning of the hip which might be comparable to the baseball step in slinging. Another move comes from the wrist where the club blade is turned and the club is additionally swung forward. Similar motions where the sling gets a kick with the wrist are probably also used in slinging.
Back to top
 

Slinging since 2005-09-24.
WWW  
IP Logged
 
Gun
Interfector Viris Spurii
Past Moderator
*****
Offline


Slinging  Viking

Posts: 1089
The Ozarks of Ark & Mo
Gender: male
Re: The physics of the sling
Reply #40 - Sep 24th, 2005 at 9:45am
 
Quote:
One very important move is the turning of the hip which might be comparable to the baseball step in slinging.


I use that method baseball step method. I call it the womens fast pitch softball throw. You get some longer ranges with it i believe.
Back to top
 

"A Knifeless man is a lifeless man" Old Nordic Proverb
 
IP Logged
 
Rodders
Tiro
**
Offline


when a date falls from
heaven open your mouth

Posts: 17
uk
Gender: male
Re: The physics of the sling
Reply #41 - Jan 9th, 2006 at 3:22pm
 
Almost obsessive. i have kept a diary of what works and what dont for the past three years. and in my best shots the energy starts from my legs surging up through the back, shoulders, forearm and final flick of the wrist a fair amount of passion tipped  malice i bang that shot out in a base ball come spear throw finnish. ow and hope i kill nothing but the undergrowth. Wink the point im making is for all the physics involved its still a case of skill, muscle, and hope to me.  8)
Back to top
 
 
IP Logged
 
simia
Junior Member
**
Offline


"sumus romanus et non
barbari" latin

Posts: 64
cleavland-akron
Gender: male
Re: The physics of the sling
Reply #42 - Feb 3rd, 2006 at 11:36pm
 
i was bord during study hall today so i came up with a  formula to calculate the speed of the projectile( not to bad for a freshman algebra 1 student) and looking for insite if it is correct.  .  then multiply the lenth of the sling, Both sides including the pouch, by pi.  you then divide this number by the time the total time it takes for the sling to make a full rotation.  this should give you the feet per second for the stone.  i couldn't get outside to get an accurate reading ( Ohio rain in febuary, suposed to snow 6 inches tomarro) but my calculations for indoors is about 90 fps but keep in mind that i just started slinging about 3 days ago so i probubly can get much higher the longer the sling and fast the swinging
Back to top
 

vita gladio, mortis gladio Live by the sword die by the sword
simia+6+6+1943  
IP Logged
 
Matthias
Past Moderator
*
Offline



Posts: 1418
Gatineau/Ottawa QC, Canada
Gender: male
Re: The physics of the sling
Reply #43 - Feb 4th, 2006 at 12:54am
 
Hey, Great (!) this thread got resurrected.

Simia - you are on the right track. Unfortunately, for most slinging styles, the majority of the acceleration is imparted during that last revolution. I use two styles predominantly: a single windup underhand/sidearm and the fig-8 (although I'm trying to develop a solid "Bernini" too*) During an underhand, I don't start putting enrgy into the throw until the sling is over my head, with only 180 deg left to travel. The fig-8 is similar, with most of the fancy footwork just being setup for a fast overhand swipe.

If you break down that last 180 deg further, you'll find that acceleration is usually increasing until the "snap" at release, where you spike. Velocity moves even faster. With a fig-8, I expect that I go from something closer to 10m/s up to 40-45 during the last 90 deg of the throw.

I did a quick analysis of some video a ways back and found that the timewise resolution was just too slow to work out the speeds in the last part of the throw. Durin ghte windup, 30 frames a second gives nice short steps, but the 40-70 that we are capable of ends up being too fast. You get something like 10cm, 10cm, 10cm 12cm, 80cm, where did it go ??? I'm still hoping to find/make a stroboscopic flash that can freeze the throw at (say) 200Hz steps, but no luck so far.

Matthias

*
note the newly named sling style... try it, you'll like it!

Back to top
 
 
IP Logged
 
bigkahuna
Slinging.org Moderator
*****
Offline



Posts: 3894
Delaware, USA
Gender: male
Re: The physics of the sling
Reply #44 - Feb 4th, 2006 at 5:04am
 
OK, How do you do a "Bernini"? ???
Back to top
 

Give a man a fish and he will eat for a day. Teach a man to fish and he will sit in a boat and drink beer all day.
John Walker  
IP Logged
 
Pages: 1 2 3 4 5 
Send Topic Print
(Moderators: Rat Man, Mauro Fiorentini, David Morningstar, Chris, Masiakasaurus, Curious Aardvark, Bill Skinner) - (Moderator Group: Forum Moderator)