As an aspiring physicist and engineer, Accelerator is one of my most favorite characters in any series sheerly because of the nature of his power. Now, I've recently gotten around to watching this episode and--as an aspiring physicist and engineer--I find it utterly inconceivable that Accelerator can be man-handled by Kihara like that (given the nature of Accelerator's powers).
*NOTE 1* I'm fully aware that this is a fictional series written by an author who has very very disillusioned conceptions about classical mechanics.
Premises
Now, thinking back on the episode, I had to think hard about the way Accelerator's power works and Kihara's "explanation" of how he bypassed redirection. I'm going to go ahead and establish some axioms here.
1. Accelerator - The basis of redirection is that his power automatically reverses incoming vectors at "random". I say "random" instead of harmful because he can eat, drink, and see (remember that the way our eyes work is that light reflects off of objects into our retinas)--yet things like the sunlight etc. are reflected away.
2. Kihara is a normal human, without modified bones or muscle structure. As far as the wikia is concerned, this would appear to be the case.
Redirection
Now, I believe Chaos2Frozen's explanation of the way redirection works, and how Kihara bypassed it is a good summary in layman's terms of what exactly transpired in Kazuma Kamachi's (the author) imagination. Here's an appended quote to refresh everyone's memory:
Quote:
Originally Posted by Chaos2Frozen
Redirection automatically reverse the vector of anything it deems as harmful in the opposite direction. Kihara simply reverse the direction of his attacks at the last nanoseconds before Redirection kicks in and instead reflect the attack right into Accelerator.
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Now, this should somewhat make sense to anyone not entirely familiar with physics; however, to those with trained eyes this makes absolutely no sense, and I'm about to explain why (by the way, dragon132004's diagram on page 12 made absolutely no sense, but kudos for trying, the time-axis was a nice touch but had utterly nothing to do with anything at hand).
What it means to Punch (A Physics Refresher)
Let's ponder for a moment about what it actually means to punch someone. When you punch someone, basically the specifics of what's happening is a series of muscles contracting and relaxing to exert a force on your fist *NOTE 2*. If we recall our 2nd or 3rd day in physics class, we'd remember that the definition of a force is the acceleration of a mass, in this case the acceleration of a fist. When the fist actually reaches the target and hits them, what actually determines the amount of damage done is not the amount of force the fist is experiencing at impact, but the
momentum of it.
Why is getting hit by a train moving at constant velocity more scary than getting hit by a car that has been accelerating for only 1 second? (The key proponent here is that the train is experiencing a net force of zero and the car is experiencing non-zero net force)
We remember from class that the answer to this is: "because the train has a hell of a lot more momentum than the car (unless the car accelerates to very very very large speeds in the one second interval)." *NOTE 3*
Now, back to the fist flying towards my dear pal Accelerator's face. When you want to punch someone, the reason why you fire your muscles as hard as you can is because you want to exert as large a force as possible on your fist: the goal is to make the velocity of your fist as high as possible before colliding into your target's face (trying to reach maximum momentum).
What determines the amount of damage when you hit someone, is how quickly your fist decelerates from it's previous momentum. This is generally called the "impulse" in physics courses. Recall *NOTE 3*, and you can see that in order to decelerate an object to zero momentum (zero velocity) it takes a certain amount of force (deceleration is negative acceleration). Depending on the time it takes to decelerate, the amount of force an object must experience to reach zero velocity can be very very large (a train, for example because the mass is very large; and an electron for example because of how fast it is).
Where Shit hits the Fan
Finally here's where Kihara's little strategy starts falling apart. Apparently he merely pulls his fist back right when his fist is in the AIM field where the vectors are automatically redirected, thus making his fist that is experiencing a negative force *NOTE 4* now experience a positive force.
Let's imagine the FBD of Kihara's fist right before it strikes Accelerator, inside of Accelerator's AIM field. There are two vectors of interest here *NOTE 5* momentum and net force. When Kihara says he's "pulling his fist back" right before striking, this is just vague enough to mean several different things:
1) Fist momentum is positive, net force is negative.
2) Fist momentum is zero, net force is negative.
3) Fist momentum is negative, net force is negative.
Scenario 1: After redirection, momentum is now negative, and net force is now positive. Basically, axes are reversed. Fist is flying towards Kihara's face, but is experiencing deceleration (probably won't reach target). In order to hit Accelerator, the amount of force must be great enough that the momentum changes from negative to positive (with respect to Accelerator), and the fist must attain a good momentum to deal respectable damage to Accelerator's face. Now, apparently the order of magnitude that Accelerator's redirection operates is in nanoseconds. NANOSECONDS. That's 1x10^-9. The amount of force in the impulse (change of momentum) in a nanosecond to make ANY number change magnitudes will
destroy every bone and muscle in your body. *NOTE 6*
Scenario 2: After redirection, momentum is still zero, but net force is now positive. On top of *NOTE 6*, if the force is too small Kihara's best hope is that Accelerator's weakness is a soft caress on the face.
Scenario 3: This is impossible because of *NOTE 6*. He has to change the momentum of his fist within the AIM field. The best case scenario here is that the bits and pieces of what used to be his arm before it exploded into a bloody mess gets redirected towards accelerator and forces him to take a shower.
I eagerly implore other posters to help me swallow what I conclude to be Kihara's utter bull-shit, but if there is no answer then I guess the only thing I can do is wait for him to get destroyed along with his ridiculous deus ex machina in a few episodes when he is transformed into a projectile.
Phew, that was quite a bit to type but I felt like I needed to get that off my chest.
*NOTE 2* Your entire arm actually experiences a myriad of forces, but we're chiefly interested in the effects of the fist on Accelerator's face, so let's just worry about the way the resultant vector of these forces are like when they reach Kihara's fist.
*NOTE 3* Momentum is defined as a moving mass, e.g. mass w/ velocity. We can see plainly that a force (acceleration of a mass) changes the momentum(velocity) of an object.
*NOTE 4* Negative force means acceleration in the opposite direction, where positive means towards Accelerator's face, and negative is directly away.
*NOTE 5* Momentum of the fist, the net force on the fist, and torque on the fist. We're ignoring torque, because it holds no relevance to this scenario.
*NOTE 6* Let's say start velocity of a 1 kg mass is -10 mps, and ending velocity is 10 mps (respectable speed for a fist imho). The average impulse in 1 nanosecond is 10-(-10)/ (10^-9) = 20x10^9 = 20 BILLION Newtons. To put this into perspective, that's about enough force to launch a Saturn V rocket into space two hundred thousand times, and Kihara must exert this force on himself in a nanosecond. I guarantee the results will not be pretty.
.
? Say it isn't so!
