So recently I became quite interested in the actual working of the sling in order to reproduce the results that ancient slingers supposedly could achieve (hitting enemies 400 meters away with 1-pound weights). This came about because I was writing a midterm exam on classical mechanics for one of my physics classes (I teach at a local college) and, lacking other inspiration, I had them calculate how many rotations a second a slinger would need for a 400-m shot, and what the tension would be ...

Here's the upshot (no pun intended): Suppose you want to shoot a 1-pound weight 400 meters. And say you do it at a 45-degree angle, which (ignoring air resistance) would give you the greatest range at a given launch speed. Your launch speed would have to be about 63 m/s -- let's say 70 if you take into account air resistance and that you'd probably want a lower launch angle as it gives you better aim and these numbers are supposed to refer to accurate shots. If the cords of your sling are 1 meter long, then that would mean you'd need and angular velocity of 70 radians per second, or a little over 10 revolutions per second. And most images seem to depict slightly shorter slings, so you'd actually need more revolutions per second.

So then the tension in the cords (all together added up) would be mass times velocity squared over radius, or about 2000 N (rounded) -- roughly equivalent to the weight of 400 pounds. For comparison, that is about half the force required by modern Olympic hammer throwers -- however, those use two hands and their own body weight for balance.

A more conservative estimate -- say half a pound weight over a slightly shorter distance would still leave about 500-1000 N. This might be realistic, although it still seems really quite phenomenal to me, and suggests that a great part of the life-long training of Rhodian and Balearic slingers, say, was not just accuracy but also pure strength. Especially since the cords seem to be mostly supported through the motion of the wrist rather than the whole arm. It also means that unless slingers practiced on both sides rather than just their dominant hand they must have had somewhat asymmetrical bodies.

Or am I missing something here in terms of sling techniques?