I am a motorcyclist who knows very little about physics 🙁
Motorcycle jackets and trousers have impact protectors: padded thingies in the impact areas (back, elbows, shoulders, knees, hips) which are meant to protect us in case of an impact, absorbing part of the impact and transferring less force to our fragile bodies; see https://www.d3o.com/products/t5-evo-pro-x/
This British company makes armour which is softish, but hardens on impact:
https://www.d3o.com/what-is-d3o/
My question is: is this a good thing, and why? Wouldn't I want the armour to stay soft, rather than hardening on impact? How does impact absorption differ with hard vs soft materials? Which transfers more force to the body and why?
After all, if I hit a wall, I'd much rather have a soft mattress, not a hard steel plate, softening my impact. Am I missing something?
On motorcycle forums there are mixed opinions on this, but I'd like to understand the physics behind it – single experiences (I came off with this type of armour and I did/didn't hurt myself) mean very little.
Thanks!
PS The site warns me the question appears subjective, but it is not: I am asking how force absorption differs, not who prefers one kind over the other
Best Answer
The ideal case for a motorcycle would be a hard shell with either energy absorbing restraints and harnesses or soft padding. This is the tested paradigm in modern race cars.
A hard shell albeit one designed to absorb huge energies in a crash where calculated sacrifice members of shell will crumple and will act as a safety cage and the harness or padding will reduce the deceleration to a level that delivers a manageable blow to vital organs.
The breaking of a crash into several softer stages is to go through most crashes with no damage and a potential really bad one with less damage.
Another factor is the rider. A good fall even in a fast crash and anticipation of trajectory of body and protecting the head could be the difference. I do powder ski and try to roll into a crash once it is past point of no return. I have practice my portfolio of moves and do not waste time thinking what to do!