woah! Physics...

Though I have to agree, not just because it's science in action, but it becomes quite visible with various tests.  When using a thicker line, I have had problems bringing up the speed of my casts to what I can do with a sling having smaller diameter lines.

Those are several excellent points ripcord.

My generic slings are fairly thin (but sufficiently tough).  I use paracute cord, which is light and strong.  These always produce good results with marble to golfball sized rocks.  I can get about 300 feet range with a 2-3 foot sling. 

I'm starting to wonder if a super sling comprised of very light, high-strength materials could be attempted by myself or another interested person on this forum.  You could pick up some nylon cord or something similar cheap.  If it's too thin, you could always braid it.  You'd have to make better ends so it didn't hurt your hand if you wanted to use something like fishing line.  Any fishers here?  What is the strength of those cords?

As for a pouch, you could probably find some "super fiber" fabric at a hardware store used in some random product.  Any ideas?

You might be able estimate the potential gain in energy by finding the wieght of the stone and the sling (perhaps only the lower 1/3 to account for the centripital acceleration mainly affecting the pouch and lower region of the cords) and see what the ratio is.  Then you could estimate the new sling's weight and see how much the ratio jumps.  That would give you an idea of how much additional energy the stone will gain. 

Off the top of my head, I would think that even cutting the wieght in half wouldn't have a significant effect.  However, the reduced air friction from thin cords in addition to any benefit from the reduced weight could be noticable.

Thoughts?
Chris

I think the key point you made Bill dealt with experience.
If an "improved" sling is not controllable, what's the point?  But if "somebody" can still maintain control then they, at least, are ahead of the game.

Also consider the sling that is too long, when using "conventional" materials.  If the new materials don't allow control for a standard sling length, they may be just the ticket for a longer one.

Spyder line is something I've only heard of and my naps...er, fishing days along the river banks are long gone.  A favorite fishing line back then was braided nylong, usually black.  It came in a variety of tensile strengths, some plenty strong enough for slings.  I've had cause to look for it again over the last couple of years, but none of the local sporting outlets carry anything like it anymore.  Oh well.

I happen to have a fair amount of another nylong string. It's 3-twist and a pain to handle, but is pretty strong.  I may try that sometime.

Pouches:  It just so happens that recently a gentleman offered a pretty neat method for constrcting net pouches.  Although intended for trebuchets, it is still a sling and pouch and designed for spherical objects.  Let's see if I can get the URL correctly posted here:

[url]http://boander.home.att.net/Sling.html[/url]

Well, not what I had in mind but it works.  Also check the little yellow diagram found at that page. It will lead you to pictures and such of his design and pouches.

In fact, I have only the original TBT siege engine, along with several other types as well.

I also have several fishing line slings for them. One of the best materials I've used though is "mason's line", also called "surveyors line".

It is usually yellow, although it comes in other colors as well.  Made of braided nylon and roughly 1 mm thick.  Very cheap at the hardware store and can be found almost anywhere.

Mmm...gives me a thought for another topic.

I have made slings of very thin 40lb test icefishing line, but they were awful performers.

How about using the trebuchet to do controlled tests of various sling materials and designs??

Just speculation, but I suspect there may be some benefit from using cords with just a small, but right amount of stiffness and torsional rigidity.    This benefit might not show up in trebuchet tests, but might be apparent in hand-slinging.

It would be VERY interesting.  A sling with two 36" lengths of 1/8"diameter line presents 9 square inches of frontal area, to be acted upon by air resistance.  That's a LOT!!

mgreenfield

I found the following post on a physics site and had to post it here
MadSci Network: Physics

--------------------------------------------------------------------------------


Re: how works a sling of dave?
Date: Wed Nov 1 19:42:22 2000
Posted By: Benjamin Monreal, Grad student, Physics, MIT
Area of science: Physics
ID: 972417100.Ph
--------------------------------------------------------------------------------

Message:

Bonjour Dirk,

In the Biblical story of David & Goliath, David uses a sling to throw a small pebble hard enough to kill Goliath. Now, I've never killed a giant, but when I was younger I used a sling to throw rocks 100 meters across my back yard.

It is not a complicated device at all; the idea is to throw something by swinging it around really fast and letting go. But there's some physics behind that which of course I will talk about first.

You can think of a sling as a way of storing energy from your muscles. To throw something really fast, you want to put as much energy into it as possible. But your arm, while it's perfectly happy lifting twenty kilograms fairly slowly, can only deliver small amounts of power during the half-second exertion of throwing a baseball. You'd get that ball going faster if, somehow, you could put energy into it slowly - the way your muscles work best - and have the energy converted into forwards motion all at once.

There are lots of ways to store up energy like this; a bow and arrow is an example. You draw the bow very slowly, storing energy in the springy bending of the bow, and all of that energy is released quickly into the arrow. A crossbow allows you to store up even more energy, if you use a crank to draw it. Imagine if you build a super-stiff crossbow, you might spend half an hour cranking it back, but that half-hour's worth of effort all goes into the arrow at once. A golf club is another approach; when accelerating a golf club, you have a long, long stroke - much longer than the "stroke" of throwing a baseball - during which to accelerate the club head, so it's going very fast when it hits the ball. Meanwhile, your arm and shoulder muscles didn't have to move very fast at all.

Anyway, a sling is a simple way of putting lots of energy into a rock and then letting it go all at once. You basically use your arm to accelerate the rock, but keep it on a string so it stays near you, going in a circle - so you can accelerate it again and again, speeding it up, and then releasing it when you've gotten it going very fast.

Here's very simple design!


                         cloth cloth cloth cloth
string string string strinloth cloth cloth cloth string string string strin
                         oth cloth cloth cloth c                  (tie a
                         th cloth cloth cloth cl                  loop in
                                                                  one end)
Use about 75 cm of string on each end, and maybe 25x8 cm of cloth in the middle. One string's end gets tied onto your finger, the other is held in your hand. When holding the two strings, the cloth hangs below and makes a little basket. Put your rock securely in the basket. Now, go to a WIDE OPEN SPACE, swing the rock-in-basket around above your head until you get it going really fast, and let go of the free string! The basket opens up, the rock flies out and sails away!
Yes, it's really that simple. And yes, a rock thrown like this can seriously injure someone. The only thing limiting the speed of the rock, now, is air resistance. When you're spinning it really fast, the amount of energy you put in with your arm is about equal to the amount taken out by drag forces - you'll be able to feel this. It'll feel like the rock just can't go any faster. That's all I'll say about physics, and I'll end with a safety notice (I work with NASA; we make a big deal of safety).

WARNING - not only is the rock going very very fast, but it's also terribly hard to aim, until you've practiced a lot. I mean, REALLY REALLY hard to aim; be prepared to deal with the consequences if the rock goes completely behind you, or sideways, instead of forwards. Not only is it hard to decide when to let go of the string, but also sometimes the rock will fall out of the basket on its own. So start with small projectiles (small pebbles, crabapples) and stay far away from people, and windows, and Goliaths!

Have fun, and be careful!

-Ben Monreal