If Quicksilver can go that fast, if he didn't hold the person’s neck while running with them would his sudden burst of speed snap their neck? Or would they just have whiplash like in X-Men: Days Of Future Past?
This video (Game Theory: Hookshot) discusses the degree of acceleration a human body can withstand (starting at around the 12-minute mark), and the mathematics thereof.
Judging from physics and human physiology, rather than any canon source, it doesn't seem possible that Quicksilver could move a person as quickly as we see in the film without causing them severe injury.
The maximum acceleration a human has ever survived was a peak of 46g on a rocket sled which accelerated to mach 0.9 (source: http://en.wikipedia.org/wiki/G-force#Human_tolerance_of_g-force). However, there is also the un-cited claim that such acceleration caused permanent vision problems.
- Mach 1 is just over 761Mph.
- The muzzle velocity of a 9mm bullet is 1029Mph.
In the film, we see Quicksilver easily outrunning what appears to be 9mm ammunition (although it could be 45 caliber); if he is accelerating a passenger to anywhere near those speeds, he would almost certainly kill them.
Although the question offers two possible outcomes (snapped neck or whiplash), a third outcome seems most likely (and terminal): The person being transported would suffer fatal internal injuries because the forces of acceleration don't play only upon the outer husk of our bodies and our fragile necks, but upon each and every component therein.
The brain of a "shaken baby" is injured by bouncing against the inside of the skull. People in closed spaces exposed to the shock waves of explosions suffer internal injuries at least partly because the shock waves act upon their organs as well as their limbs, trunks, heads, etc. Thus, not only would the head be snapped backwards if unsupported, but the brain within would be snapped back into the back of the skull even if the head were supported. The stomach, kidneys, liver, lungs etc. would be pressed back against the spinal column with pulping force... and you get the picture.
The only way this could play out and end up with a living passenger at the end would be if there were some sort of "magical" or "super science" chamber effect surrounding their person which slowed the effects of acceleration similar to the way a decompression chamber slows the body's treatment of dissolved inert gases in his/her blood and joints when surfacing from a deep dive. If the person being transported could be held within a delaying sphere of some influence that allowed the compression forces to be played out over a few moments before and after arrival instead of taking place nearly instantly, the forces on the entire body could perhaps be absorbed in a less injurious way.
Of course, this seems unlikely since the force is the movement and thus the delay would have to be in space as well as time - kind of eliminating the speed of the transport and thus the premise of the question. Oh well... but fun to think about.
TL;DR yes, quicksilver cannot run (alone or with someone) without a bunch of implicit secondary powers (that would be very usefull but that he never uses ^^ )
This is a typical case of secondary powers required...
Like for superman, flash and all others that go to great speed, they have to have some implicit powers in order to achieve what they do without breaking all laws of physics... They need :
a sort of energy field that remove the inertia (to suppress the acceleration and not crush whatever they are holding, or themselves)
a superforce to support all efforts they need to make to run this fast and resist acceleration
a super resistant costume (or else it would shred immediatly)
a way to harden the floor or else they would create big holes (every time they start running or stop they apply a demential force to the ground)
super eyes to see what's coming in the way
super rapid thinking to have the time to react
I am not a doctor or a physics major but from the movie X-men: Days of future past when Quicksilver held Magneto's head and accelerated/moved from standstill to his destination. It only took a split second, it seemed almost instant. One would think this would for sure snap the person neck or give them serious injuries.
Here is the logic, in the movie we see Quicksilver can run much faster than a bullet travels. A bullet shot at a person can go right through them or get stuck deep inside of the body depending where it hits. So since Quicksilver runs at a much faster speed, it would be like a cannon ball hitting a person if Quicksilver happened to run into someone by accident. When a truck hits a person at even 100 km/h, the person would most likely to be dead. Since Quicksilver is so much faster, running with someone without holding their head would most likely kill them. If you get into a car accident when someone hits your car from behind, there is a good chance that you will get whiplash.
So given the clues above, logically I think it would make sense that if Quicksilver did not hold magneto's head, he would of probably killed him or seriously injured him.