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Question: Lobbing vs. Throwing

Lobbing    
  5 (12.2%)
Throwing (flatlining)    
  19 (46.3%)
Both have their place    
  15 (36.6%)
I like to kick rocks.....    
  2 (4.9%)




Total votes: 41
« Last Modified by: TheSlingin-Injun on: Nov 18th, 2013 at 9:20am »

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Lobbing vs. Throwing (Read 38565 times)
Thearos
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Re: Lobbing vs. Throwing
Reply #45 - Nov 19th, 2013 at 12:01pm
 
But what is the loss of speed of the stone ? There's the rub. Apparently, a pitched 150g baseball loses .44m/s every 2m or so. A So over 20m, that would be a 4m/s loss. Let us assume that a heavy stone loses less than that. So my completely made up guestimates of speed at impact are perhaps roughly OK.

I hope Aussie would have found this interesting.
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Dan
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Re: Lobbing vs. Throwing
Reply #46 - Nov 19th, 2013 at 3:17pm
 
In order for me to actually throw a stone with a noticeable arc at less than 40 yards, its more like 50% of the original power of the throw, even with tennis ball sized rocks of quartz.

This thread convinced me to practice lobbing more, and I did. I was actually less accurate because it felt like I was 'forcing' a weak throw.  After some practice it wasn't too bad, but even slinging 110% (normally not very accurate) was more accurate than lobbing for me.

So if there is significantly less velocity and KE and no accuracy advantage (usually less accuracy), it's really not very helpful to me at least, perhaps others can find more use for it.

Lobbing also cuts down on the sling's ammunition versatility. If you require such heavy ammo to sling pretty much every thing egg sized and under is out.

Don't take the above as animosity, I'm just explaining why I find flat lining superior (as apparent by the poll, most people already do).
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"Like tying a stone to a sling is the giving of honor to a fool" Proverbs 26:8
 
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Thearos
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Re: Lobbing vs. Throwing
Reply #47 - Nov 19th, 2013 at 4:53pm
 
Trying to adjust my figures--

Shooter B, lobbing a 200g stone at 30m, with a 37m/s initial velocity, will have (I assume) a better velocity retention than a pitched baseball. The pitched baseball would lose .44m/s every 2m, so about 7m/s over 30m, so the velocity of the stone on impact would be BETTER than 30m/s, so KE > 90.

Shooter A whangs a 80g stone at 30 m, with a 48 m/s initial velocity; we assume the same loss of velocity (i.e. something like a pitched baseball, not so good, though, as the heavier stone), so around 41 m/s at arrival, so perhaps a mite above 67 J, or even a bit lower if drag and speed loss is significant.
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Thearos
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Re: Lobbing vs. Throwing
Reply #48 - Nov 19th, 2013 at 4:56pm
 
"Good news for batters, the "muzzle velocity" of a pitched baseball slows down about 1 mph every 7 feet after it leaves the pitcher's hand"

http://www.bostonbaseball.com/whitesox/baseball_extras/physics.html

1 mph = .45 m/s
7ft=2m 13.
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Masiakasaurus
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Re: Lobbing vs. Throwing
Reply #49 - Nov 19th, 2013 at 5:31pm
 
Smiley I like where this thread has gone.

Thearos, your math is good. I don't know about your assumptions on skin friction, though. I will find some measurements for a hand filling stone and calculate the drag on a smooth sphere in laminar flow to give us an idea how quickly the stone will decelerate when we neglect acceleration due to gravity.

FD=1/2ρv2CDA

Stop focusing so much on maximizing energy, guys. I maintain that in ballistics it is momentum transfer that is important, not energy transfer. And, lucky for us, in the equation for momentum (p=mv) both mass and velocity vary linearly.

Edit: Found a primary source for Maori sling stone dimensions close to the size of a baseball. I'm using 84mm in diameter and 28 oz for my calculations.
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Pikåru wrote on Nov 19th, 2013 at 6:59pm:
Massi - WTF? It's called a sling. You use it to throw rocks farther and faster than you could otherwise. That's all. 
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Thearos
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Re: Lobbing vs. Throwing
Reply #50 - Nov 19th, 2013 at 6:00pm
 
I think both points-- that re. drag, I have no idea what I'm talking about, and that momentum transfer must be what matters-- are very well put, and show how my laborious calculations are mere possibilities and starting points, nothign definitive.
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Re: Lobbing vs. Throwing
Reply #51 - Nov 19th, 2013 at 6:15pm
 
I don't mean to sound arrogant so please do not take it that way, but I have a set  of 42g darts that I use. this is very light to me. The stones that I am "flat lining" at over 25 yards are between 180g minimum and 260g maximum. you can see the size of rocks I use in my videos and I have weighed them. Point being. Thearos, The dramatic weight difference that you are using in your examples is what is misleading your math. you have doubled the weight in your example and only have a velocity difference of 10 m/s. this is also misleading. As I have not done chrony tests it is impossible for me to speculate accurately on the actual velocities, but I can assure you it would exceed the proposed 10m/s.

Where was I going with all of this Huh
coffee time Wink

you do not have to decrease to weight of the projectile that much to gain double the velocity. Lets not forget to, that this is all depending on the persons physical capabilities and how well they can harness the mechanical advantage gained by the sling. I am assuming that by your examples a 200 gram stone is heavy to you. where I would find something exceeding 350 grams heavy(a weight I would need to lob)

use a slightly lighter rock than one you would need to lob and you will gain much more velocity/ power. or just strengthen your muscles and practice maximum efficiency with the larger rock and before long you will be rocketing that bigger rock. win...win. Cool
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Masiakasaurus
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Re: Lobbing vs. Throwing
Reply #52 - Nov 19th, 2013 at 6:24pm
 
At 20o C and 101.325 kPa, dry air has a density of 1.2041 kg/m3

I will borrow vi=50 m/s because I have no clue what to make up in its place.

CD=0.47 for a sphere

A=πr2=0.005541769 m2 or 55.41769 cm2

So:

FD=0.5(1.2041 kg/m3)(50 m/s)2(0.47)(0.005541769 m2)=
3.92029588108 N


Given a mass of 28 oz or 0.793787 kg the acceleration is going to be roughly
4.9 m/s2
in the free stream direction at the moment of release.
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Pikåru wrote on Nov 19th, 2013 at 6:59pm:
Massi - WTF? It's called a sling. You use it to throw rocks farther and faster than you could otherwise. That's all. 
~Engineers like to solve problems. If there are no problems handily avialable, they will create their own problems.~
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Bill Skinner
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Re: Lobbing vs. Throwing
Reply #53 - Nov 19th, 2013 at 6:26pm
 
Mas, I think the weight in the pictures are wrong.  I think somebody long ago messed up converting grams to ounces.  Rock A is 2/3rds the size of rock B but is 1/2 the weight, Rock C is is 3/5th the size of B but only 1/4 the weight.  Something isn't correct.
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Masiakasaurus
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Re: Lobbing vs. Throwing
Reply #54 - Nov 19th, 2013 at 6:38pm
 
Bill Skinner wrote on Nov 19th, 2013 at 6:26pm:
Mas, I think the weight in the pictures are wrong.  I think somebody long ago messed up converting grams to ounces.  Rock A is 2/3rds the size of rock B but is 1/2 the weight, Rock C is is 3/5th the size of B but only 1/4 the weight.  Something isn't correct.


Well, that sucks. Let me compare it to a baseline density for basalt of 2.8 g/cm3. (Thank you, ask.com!)

V=4/3πr3=0.000310 m3=310 cm3

2.8*310=868 g=0.868 kg

I'd call that acceptable error, but since I have a new mass for the sphere:

a=4.51646990908 m/s2
in the free stream direction.

Now, the force due to drag will vary with the square of the velocity but we can use snapshots with respect to velocity to approximate it since we know that it is parabolic. If I were a nice person I'd calculate the drag at a couple more velocities and draw a graph, but I'm not going to. Tongue
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Pikåru wrote on Nov 19th, 2013 at 6:59pm:
Massi - WTF? It's called a sling. You use it to throw rocks farther and faster than you could otherwise. That's all. 
~Engineers like to solve problems. If there are no problems handily avialable, they will create their own problems.~
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Re: Lobbing vs. Throwing
Reply #55 - Nov 19th, 2013 at 6:49pm
 
now this is really getting silly. Grin

Ok. enough numbers for a while.

Cave man thoughts on momentum.....

Throw big rock, fast.....smash Angry
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Masiakasaurus
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Re: Lobbing vs. Throwing
Reply #56 - Nov 19th, 2013 at 6:52pm
 
English_Marauder wrote on Nov 19th, 2013 at 6:49pm:
now this is really getting silly. Grin

That's my job!

Also worth noting: I'm assuming all of this is happening at substantially less than transonic speeds, so no parasitic drag. It's isothermic, laminar, and incompressible flow that is fully attached where M<0.2. In English that means it's a windless day at room temperature with no humidity, the rock is smooth as glass, and it's not flying any faster than 1/5 the speed of sound at that altitude.
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Pikåru wrote on Nov 19th, 2013 at 6:59pm:
Massi - WTF? It's called a sling. You use it to throw rocks farther and faster than you could otherwise. That's all. 
~Engineers like to solve problems. If there are no problems handily avialable, they will create their own problems.~
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Re: Lobbing vs. Throwing
Reply #57 - Nov 19th, 2013 at 6:59pm
 
Massi - WTF? It's called a sling. You use it to throw rocks farther and faster than you could otherwise. That's all. 
~Engineers like to solve problems. If there are no problems handily avialable, they will create their own problems.~

Bill - Basalt can have different densities depending on how it is formed such as much time it has taken for the magma to cool after it has been extruded. On an island, magma may have cooled under water or under limestone long before it was pushed to the surface above the water. It's possible the measurements on that illustration are accurate because what is not provided is the stone's density.
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I sling. Therefore I am. Tano' Hu I Islan Guahan. http://itanohu.blogspot.com
 
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Re: Lobbing vs. Throwing
Reply #58 - Nov 19th, 2013 at 7:12pm
 
Mr Marauder:

1.  the velocities I give are pretty much within the range of what is recorded-- between 30+ and 50+ m/s. You can play around with the figures, but the general outcomes and orders of magnitude all seem to point the same way.

2. The point is not what you find light or heavy. It simply to show that a perfectly respectable weight (80 g) slung fast produces less KE than a heavy stone (200 g) slung slower, but still at a good speed.

If you sling 250g fast, then 400 g lobbed a bit slower would produce greater KE. Scale all my figures up if you wish-- it's the general point that matters here.

The point being to confirm something seen instinctively-- the smashing power of lobbed shots-- but which the love of whanging has obscured.
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Re: Lobbing vs. Throwing
Reply #59 - Nov 19th, 2013 at 7:16pm
 
Thearos wrote on Nov 19th, 2013 at 7:12pm:
The point being to confirm something seen instinctively-- the smashing power of lobbed shots-- but which the love of whanging has obscured.

The love of whanging, and the use of the equation for KE rather than the equation for momentum.
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Pikåru wrote on Nov 19th, 2013 at 6:59pm:
Massi - WTF? It's called a sling. You use it to throw rocks farther and faster than you could otherwise. That's all. 
~Engineers like to solve problems. If there are no problems handily avialable, they will create their own problems.~
WWW elsabio04  
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