Originally Posted by
avole
To answer your last question, < .001%. You, surely, must see that helmets provide 1 or 2% max extra thickness, so a helmet that hits the ground at, say 8 kph, is going to provide lots of protection, whereas it would have to hit it at, say, .0001 kph to avoid any damage? I'm assuming the head is decelerating at a good rate, by the way, with which most experts would argue. In either case, the downward force is not going to cease in the 1 - 2 cm protection the helmet provides....
Well ... the helmet is 1 or 2
inches extra thickness, not 1-2%, and the nominal reason that a helmet protects against TBI is that when that thickness crushes the impulse is spread out over time. Which presents lower force to your skull. This does result in lower risk of traumatic brain injury, but of course does not prevent it.
It isn't really known whether the extra thickness increases the chance of banging your head, though you'd expect that to be the case. Secondly, it's also not known for certain but generally accepted that it's rotational forces that results in more of the TBI injuries than linear impact. The extra thickness (presenting a longer lever against the ground) may actually exacerbate that risk, but that also lacks supporting data.
Originally Posted by
avole
You have to wonder, don't you. I'm sure this post is meant to be humorous, ....
He is making a logical point, a pretty good one actually.