The Martial Unity

Rui lost track of time as he grew immersed in fleshing out the theoretical frameworks of the two projects. The many possibilities that existed with Project Muspelheim were, in particular, difficult to parse through.

"Friction is not a bad idea for a heating technique."

In fact, friction was the reason that all mechanical processes yielded heat. It was an extremely natural source of heat and, in some mechanical processes, produced so much heat that extra cooling units needed to be put in place just to ensure that friction did not cause them all to melt.

Back on Earth, in recognition of how great a source of heat it was, there even existed welding methods known as friction welding that used the tremendous heat that friction could generate to heat up two objects and weld them together. It was especially used for metals that had high melting points and was an efficient way of getting them to weld.

It was an extremely powerful candidate for the Muspelheim technique that Rui was seriously considering.

"The issue is that it requires at least one solid object."

Friction existed the most between solid-state objects with bound molecules and atoms. If they were not bound, then these particles would only collide with each other and move away.

"It might not be fit for heaven-bending generation, but it works well with earth-bending heat generation." Rui realized.

Earth bending involved manipulating the soil and bedrock beneath one's feet to use it in combat. It was most fit for friction-heating to create the high-temperate environment of Project Muspelheim.

"Alright, friction-heating for earth-bending it is…"

That was a rather simple choice.

While his other domain techniques paid more weight to heaven-bending, he couldn't do the same for Muspelheim.

The planet was an enormous heat sink. He needed to ensure that the lands beneath his feet were equally hot; otherwise, the heat he generated in the atmosphere would only transfer to the ground, which was at a lower temperature. He would lose almost all the effort that he put into heating it up.

"I'll need to start mastering friction-heating through earth-bending as soon as possible," Rui made a mental note to the training phase of Project Muspelheim.

For each technique he created, he also needed to create an efficient and optimal training regime. In some ways, it was even more important than the theoretical framework of the technique. A poor quality training regime could not only fail to get the user to a satisfactory degree of mastery, but waste a lot of time in the process.

"Ok, friction-heating for the earth-bending aspect of Project Muspelheim, but for heaven-bending, I need something that works well with gases."

'Heaven,' in the context of domain Martial Art, was merely the atmosphere and the air around the user. It was ideal to go for heating methods that were primarily centered around gaseous heating.

"Convection is powerful, but it's not easy to control, and in gases, it also moves against gravity."

Convection was a form of heat transfer that transferred heat through the movement of heated liquids or gases. In the context of Project Muspelheim, it would mean heating his breath to an extremely high degree before exhaling and bending it to spread across the entire atmosphere.

"It will definitely yield the highest temperature, but…" Rui's expression grew complicated. "It takes more time because the quantity of breath in my lungs is limited."

No matter how powerful his lungs were, his lung capacity had firm limits. His body had a fixed size, which always meant that the amount of breath stored in it had fixed limits that no amount of training would ever improve.

The limited amount of breath per inhalation meant that it would take a lot of time to heat a lot of area.

Rui's eyes lit up as an idea popped up in them. "I…can increase the density of the air stored in my lungs."

This was ordinarily an impossible feat as the lungs of the Martial Body sorely lacked the power to convert a gas into a solid through sheer force, but the power of the Martial Heart was great enough to do that. That could partially mitigate the limited volume to a certain extent.

"I'll need to conduct several tests and trials."

While he could mathematically model the outcomes and simulate them inside his Mind Palace, it did not beat actual empiricism. However, even putting aside the outcome, heating the breath inside his lungs was not a part of heaven- bending. Heaven-bending happened after exhalation. Heating his breath inside his lungs was something that happened before exhalation.

"Even if I heat air in my lungs and exhale to heat the heavens using convection, I still need to figure out the exact manner in which I am going to bend the heavens."

Convection was something that didn't require heaven-

bending. Just exhaling heated breath would be enough for convection, but it was not heaven-bending.

Fortunately, Rui had several ideas.

"Gay-Lussac's Law." His eyes lit up with excitement. "It's perfect for this domain."

Gay-Lussac's Law was a law of Thermodynamics that governed gases. It that stated that the pressure exerted on an ideal gas, with a constant mass and constant volume, was directly proportional to the temperature of the gas.

In other words, as long as the size of a gas was unchanged, more pressure was equal to more temperature.

"If I use heaven-bending to create a domain with unchanging volume while also using heaven-bending to apply pressure to it, I can heat up the entire domain tremendously." Rui grew engrossed in the technique. "In fact, I can modify Heavenly Convergence to apply pressure to an entire domain. That way, I can skip progress by using stuff I've already mastered."

Thus, not only would he heat solidified air in his lung with pressure such that it would heat his domain with convection, but he could also then bend the heated breath to bend heaven to apply the Heavenly Convergence technique on an entire domain rather than a single person.

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