Part 11: -218°C shockwaves!? Uesugi Kenshin
Uesugi Kenshin is a warlord blessed with a mysterious allure. He combines coolness and beauty with strength as well. His faith, too, is intense; from snowy Echigo he has his sights set on the whole country, probably due to the guidance of Bishamonten* rather than personal ambition. I will take a look at the bewitching power of 'Godlike Speed, Blessed Commander' Uesugi Kenshin using science.
If it were the Olympics...
Close attention should be paid to Kenshin's speed, just as the nickname implies. First of all, there's the speed of his feet. Judging from the game screen he can run 10 steps in only 1.2 seconds. The length of a person's stride when running is a little more than their height, so here that would be 2m. Kenshin's running speed, then, is 60km/h. He can cover 100m in 6 seconds! This is the Sengoku period; unfortunately they didn't have the Olympic Games.
The speed at which he moves his sword is beyond all reason too. In particular, the trajectory of his sword can be seen approximately five times at once when he uses 'Shinretsu'. That a single sword looks as though it's tracing many arcs at the same time is probably because of afterimages. It's said that the amount of time an afterimage remains in the human eye is 0.1 seconds; this means that Kenshin is swinging his sword at least 5 times within 0.1 seconds.
Furthermore, Kenshin's sword is very long. By measuring the picture in the Sengoku Basara 2 Official Guidebook, the distance from the tip of the sword to its handle is at least 25% more than his height. If Kenshin's height is 175cm, the length of the sword is 220cm. This is more than twice the size of the imitation sword this author keeps for research purposes. A long Tachi sword doesn't suit such a slender man. The arc traced by the tip of a sword this long should have a radius of around 2.7m. When it's swung 5 times within 0.1 seconds, the speed of the tip of the sword will be 1,500km/h, or Mach 1.2! When he activates Shinretsu, Kenshin becomes a Blessed Commander with supersonic speed.
Too quick, and it won't hit
When it comes to the sword moving faster than the speed of sound, I want to draw attention to 'Shinen'. According to Sengoku Basara 2, this "creates a vacuum blade and fires it forward". Is this possible?
Thinking scientifically, the air pressure around an object moving at high speed will fluctuate, but not enough to result in a true vacuum. If the object moves faster than the speed of sound, however, something will happen. A shockwave. A shockwave has enormous energy; it's 'condensed sound' which is generated by explosions and supersonic flight. The blast has destructive force too; when a supersonic aircraft flies at a low altitude, the shockwave can break glass windows. Since it involves swinging a sword at a supersonic speed, couldn't Shinen release a shockwave too?
The shockwave comes out in a wedge shape when the sword is moving faster than the speed of sound, as shown in the diagram. However, that shockwave doesn't maintain this shape and move straight forwards when it's emitted; instead, it divides and flies to the left and right, perpendicular to the horizontal plane. At Mach 2, for example, it will fly forwards to the left and right at 60 degree angles. This means that it will defeat the enemies diagonally in front without hitting those straight ahead. The angle at which the shockwave spreads out will become larger as the speed increases. As with Shinretsu, Kenshin would probably swing the sword only slightly faster than the speed of sound to defeat the enemies directly in front of him with Shinen. Nevertheless, the energy of the shockwave's energy would be not be significantly lower. Such prudence: as expected of the Tiger of Echigo.
Less than -218°C
Kenshin's skill 'Shinjin' is exciting, scientifically. It creates a huge wall of thick ice directly in front of him. According to Sengoku Basara 2 it chills the air so the enemy is instantly frozen!
This is an amazing ability. Air is made up of 80% nitrogen and 20% oxygen with trace amounts of other gases. If water vapour can be cooled so that it becomes water, and cooled further to become ice, then as the temperature drops the nitrogen and oxygen too can change state and become liquid, then solid. Perhaps Kenshin somehow chills the air surrounding the enemy; it will first condense on the enemy's body as a liquid before being frozen further.
The temperature at which nitrogen becomes a liquid is below freezing, -196°C, and it becomes a solid at -210°C. Similarly, oxygen requires -183°C and -218°C. The fact that the air was frozen means that it would have to have been less than -218°C to freeze the oxygen as well. If it covered the body too it would be no wonder that a person would be instantly frozen!
However, there's another horrible side to Shinjin. It's when the oxygen reaches the condensation stage. When things are burned it naturally means that they're reacting with oxygen. In an area with a high concentration of oxygen, even iron will crackle and give off sparks when it burns. The oxygen atoms in its liquid form are 1,000 times more concentrated than in pure oxygen gas. For this reason, putting combustible items into liquid oxygen will cause an explosion - and the human body is combustible. In other words, as soon as the oxygen condenses, the enemy's body will explode!
That this does not happen in the game's world means that Kenshin must be freezing it so quickly that there's not enough time for it to blow up. Could he be thinking, "If they're killed by something like a bomb, they'll suffer"?
* Bishamonten is a god of war in the Japanese Buddhist tradition, and the real life Kenshin is famous for being a devout follower. Reference to this is frequently made in the Sengoku Basara series.