In reply to oldie:
> However it seems to be generally accepted that light people get less protection when using shock absorbing via ferrata lanyards, and in fact some manufacturers now produce lanyards adjustable for different body weights.
> Will not the same effect occur in a lead climbing fall with a light/child climber?
As others have pointed out, lighter climbers will decelarate more rapidly and so experience a higher g force, though being of a very short duration the importance of the g force is debatable.
Robert Durran's example above gives a g force of 7 but this would appear to be well within human tolerance for the fraction of a second it is experienced.
This suggests flopping down into a chair generates over 10g
http://www.iaapa.org/safety-and-advocacy/safety/amusement-ride-safety/g-for...
Fighter pilots wear pressurised suits to cope with g's of 8 or 9 but those forces act for a long time and would cause them to black out otherwise.
For very short durations, huge g forces can be survived
from this
http://www.medicaldaily.com/breaking-point-whats-strongest-g-force-humans-c...
"It’s difficult to calculate the exact level of G-force that would kill a human, because the duration of exposure is such an important factor. There are isolated incidents of humans surviving abnormally high G-forces, most notably the Air Force officer John Stapp, who demonstrated a human can withstand 46.2 G’s. The experiment only went on a few seconds, but for an instant, his body had weighed over 7,700 pounds"
I don't know how valid comparisons of via ferrata lanyards and climbing ropes are, they function in very different ways. A climbing rope approximates to an elastic substance hence my reference to Hookes Law (though probably not exactly because of the differential stretch of core and sheath) whilst a VF lanyard absorbs energy by a series of non elastic stitching failures.
I'm sure there's a PhD thesis in this thread somewhere but I think we can be confident that small kids falling off at climbing walls aren't going to break their backs because their rope behaves like a steel cable