Fatality Physiks no. 1: Jax's arm-pull

Blitz association. I say something and you say the first thing that comes to your mind. Ready?
Mortal Kombat.
At least some of you must have immediately thought of fatalities. It's hard not to... at the appearance of the first Mortal Kombat game, they were the blood-soaked cherry on a very gory cake. MK wasn't exactly a prime example of proper software design, and arguably the two following installments were even worse in terms of bugs and glitches. This echoed throughout the gameplay as well, with revisions being geared towards stopping misbehaving code from generating hallucinatory situations rather than the fine-tuning that was going on in the Street Fighter 2 franchise. In a time where plumbers riding smiling fantasy dinosaurs were all the rage, buckets of blood were likely to attract some attention to what was essentially an average game. And it did. To the point that the blood-letting got so over-the-top it actually became the more interesting gameplay pursuit. Playing Mortal Kombat as a discerning gamer was sort of like watching porn... somewhere in the back of your head you felt you were supporting a morally bankrupt concept, yet it delivered such a delightfully basic satisfaction. Just like I pity the teenage boy who never got his cheap fix of tits from late-night semi-erotic programs (apart from those who were more interested in the non-tit-bestowed sex), I pity whomever never experienced the joy of decapitating, de-spining or otherwise deforming their virtual opponents... let alone those who've never even witnessed it.
In some ways, this simulated violence that led to such a public outcry back in its time is laughably soft compared to what we have now. While not many games have let us so gleefully visit the most surrealistic deaths upon bitmaps or polygon collections as Mortal Kombat, they've certainly become much more realistic in any depiction of life-ending activities. Yet until the character models come with complete and fully rendered bones and intestines, all realistically destructible, today's eye-candy somehow falls short of what was basically a Tom and Jerry cartoon run out of hand. So with the current emphasis on physics in games, one can retroactively wonder (or at least I choose to do so) just how realistic those fatalities were. Would one actually be capable of executing them?
In a bid to answer this open question, the blog for YOU presents you with the first case study, the first in a series of fatality physiks: Jax's arm-ripping fatality.

Jax's arm-pull
Character: Jax
First fatality appearance: Mortal Kombat II
Appearance studied: as it is in Mortal Kombat II
Description: Jax grabs his opponent's wrists. He then proceeds to yank his/her arms off. The opponent turns to face the screen as blood sprays out of what used to be shoulders to the viewer's delight. Everybody remembers what a mescaline trip MK really was.

Anatomical analysis
A first consideration is the structure of the human arm. Jax grabs his opponent just past the wrists, so no force is exerted on the wrist joint. This means the pulling action takes effect on the elbows and shoulders. Mortal Kombat would have us believe that if such force was applied that the structure were to fail to the extent of coming loose, it would happen around the shoulder. This is quite believable... dislocated shoulders are a common injury, while dislocated elbows are a rarity in comparison. I base this on the relative number of search results for "dislocated shoulder" and "dislocated elbow" on Google. Since the force is exerted along the axis formed by the straightened arm, the bones are assumed to provide a maximum resistance to stretching and fracture. We can therefore conclude that under sufficient stress, the shoulder joint would indeed dislocate while the rest of the arm remains mostly intact.
Then we need to look at what would happen with the soft tissues. There's a shitload of muscles around the shoulder joint that are quite frankly too numerous and complex to fully analyse here, even though this is the most in-depth analysis available on the feasibility of Jax's arm-pulling fatality - I dare you to find counter-evidence for that claim. What it comes down to is that even with the shoulder dislocated, ripping those tissues would be very hard. While manageable for the rotator cuffs, ripping a thick structure like the deltoids would require near-superhuman force. Which brings us to the aspect of the agressor side.

A person with above-average strength could be deemed capable of dislocating another person's shoulders with a prodigious yanking. Tearing off someone's arms is another matter altogether. What is to be taken into account here, though, is the person executing the fatality. Let us not forget that Jax, whom apparently is capable of tearing of limbs without too much effort, ...

is the same guy who for Mortal Kombat 3 augmented his arms with bionic implants as apparently he didn't consider himself quite strong enough yet.

What it comes down to is this: if Jax were chosen to conduct an experiment to see if someone can truly rip another person's arms off with his bare hands, none of us would feel secure enough to volunteer for test subject.

Physics analysis
Anatomical considerations out of the way, let us take a look at the physics at play. We'll use the following simplified figure to illustrate the party receiving the dismembering.

The arrow denotes the direction along which the force is applied to the arms. Let's study how this would manifest itself. First of all, the point that provides counter-leverage is located at the feet. We must assume sufficient friction with the ground, otherwise the victim would simply slide forward. With said friction, the feet can be considered to stay more or less stationary. Now we arrive at a strange observation. If the body is kept completely rigid, the direction of the pull and the fact that this is done along the arms, which exceed the length of the feet, then the friction with the ground would mean the body would topple over. It would rotate along an axis situated along the toes:

Yet this doesn't happen. Alternatively, if the body of the victim was made to relax, he/she would just as well be dragged forward. In both cases this would prove to save his/her life (or at least arms, but bleeding to death is assumed inherent to this fatality). Since Jax doesn't apply any opposite force with, say, his foot, the only way this force could be there would be for the victim to lean backwards, using this angle to provide the required grip on the ground and counter rotation:

This assumes willful assistance of the victim, which is unrealistic considering the intent of Jax to get those arms off. A possibility is that this stance would be a sort of reflex naturally occurring when one is pulled by the arms, but one can not be expected to maintain it to the point of having said arms torn off.

There is one final venue for explanation, and that is to assume that the exact pull which results in the removal of the arms happens with such acceleration that the inertia of the victim's body is sufficient to provide the counter-leverage. A formula that links mass to acceleration is F = m*a, where F is force, m is mass in kilograms and a is acceleration in meters per square second. This can be rewritten as m = F/a. With a set mass, that we can estimate between 60 kilograms and 300 for the regular kombattant (there's some cyborgs in there), all but the heaviest fighters would require enormous force to bring the acceleration of their body below what is needed for keeping their arms attached. Also take into consideration that it's 5.30 AM at the time of this writing and I might be thoroughly abusing a formula that isn't relevant here.
It is imaginable that Jax's shiny metal implant-enhanced arms are capable of such force and acceleration, but how the MKII Jax pulled this off (sorry) is very debatable.
When watching the fatality played in slow-motion, we see that the exact time-interval for Jax beginning the actual pull and ripping off the arms is extremely small, indicating that this final scenario is indeed what happens here. As a matter of fact, the pull is so fast that the victim's arms effectively seem to surpass lightspeed, as evidenced by the small frame of time in which they exist in two different parts of space at once (indicated in the footage below).

Dismissing a basic assumption about maximum speed for matter and energy in physics for the sake of explaining this fatality seems to go a bit too far, so we'll keep the evaluation of this scenario at "somewhat unrealistic".

The verdict
Following points are taken into consideration, with + speaking in favour of realism, - in disfavour (that's the best antonym I could come up with).
+ The shoulder joint is a weak spot when it comes to force exerted along the axis of the arm.
- The many muscles around the joint would be hard to tear loose.
+ Jax is really strong.
- Jax is only human, as most but not even all of his victims.
- The physics don't add up.
+- It's only a damn game.

After no specific quantification of said points, the following rather arbitrary score on the realism-o-meter (ranging from 0 to 10) is awarded:

4. While not disastrous, it is below the half-way mark. Jax's arm-pulling shenanigans get the benefit of doubt, but are not lent enough credence to make us fear dismemberment by overly muscled robbers.

That was it for this installment of Fatality Physiks! This was only the first analysis, with more to follow. So watch this space! Au revoir.


Special thanks go to:
Mortal Kombat Warehouse
pages.cthome.net/mnoni/webpage/