Physics Class and an Exploration of Refrigerator Principles

The mathematics lessons were not particularly profound, especially at this stage, when they were still within the scope of "recognition"—recognizing numbers, recognizing simple geometric shapes, and so on.

They also used the raising and lowering of fingers to teach addition and subtraction within twenty.

The physics lessons that followed, however, were relatively more complex.

Unlike the other subjects, "physics" was only on its first lesson, and for the time being, Blade Tusk would teach it personally.

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"I heard it's Witch Doctor Blade Tusk—the youngest one."

"The one who created writing?"

"Yes, yes. And that 'mathematics' stuff we learned before supposedly came from his research too."

"Ah! The criminal who destroyed our childhoods."

"Oh, give it a rest. If it weren't for Witch Doctor Blade Tusk, you wouldn't even know what 'destroy' or 'childhood' meant right now."

"Haha, I was just saying."

The little ones who had entered the classroom once more waited amid the clamor of their chatter.

Before long, Blade Tusk arrived. He set the "teaching aids" he was carrying—stacked from mud boards of various sizes—beside the podium, then, without saying anything further, went straight into the lesson.

"You should already recognize the two characters 'physics,' since I spoke to your literacy teachers beforehand."

"So for this first lesson, let's get straight to what kind of field 'physics' actually studies."

He took a huge prepared mud board from the side and propped it up on a wooden stand.

Carved onto the mud board in large characters were the words: "How Does Matter Evolve?" To ensure every Troll could see them clearly, the strokes had been carefully darkened with charcoal.

"'How matter evolves' may seem like a rather broad question, but it is a very good point of entry."

"First, we need to examine the meaning of each word."

"What is 'matter'? Let's first make an assumption: all matter is composed of even smaller 'elements.' Then, if we grasp the arrangement of every 'element' in space, wouldn't that be equivalent to grasping the matter itself? Thus, matter can be extended to mean the positions of 'elements' in space. Here, we'll represent it with 'x' for now."

With that, Blade Tusk bent down, picked up a square mud board carved with an "x," and used the twisted wooden-fiber cord tied to it to hang it from a short vertical rod left on the stand.

"Now let's look at 'evolution.' We often say, 'How was yesterday?' 'How is today?' 'How will the day after tomorrow be?' That is one kind of evolution—it describes a relationship of change over time. Essentially, this is a time-dependent relationship. We denote it as 'f(t),' representing the dependence of the changing quantity f on time t. Mm, this is a 'function.' You won't encounter it until later; for now, you only need to know that such a thing exists..."

"Let's return to the question itself. In other words, 'the evolution of matter' can be expressed together as 'x(t).'"

"Next, let's look at what 'how' means."

He walked around the podium and stood before the little Trolls.

"Right now, I am standing here."

Having said that, he slowly walked to the middle of the "classroom" and spoke again.

"At this moment, I am standing here instead. The distance between us is roughly twenty meters, and during that time, I counted roughly five seconds in my head."

"In other words, I walked twenty meters in five seconds."

"Then can we know where I had reached at the second second? If I kept walking, where would I be thirty seconds later?"

"Mm, in fact, we can know. If my speed remains constant throughout, then by the second second I will have walked eight meters, and by the thirtieth second I can walk one hundred and twenty meters."

"How do I know that? Why, when we know the starting point, the time spent, and the distance traveled, can we calculate where I was three seconds ago, and even know where I will be thirty seconds into the future?"

"Returning to the question of 'how matter evolves,' what we were considering just now was actually one form of 'how.' It asks how this x(t) comes about—where this x should change to at different moments."

"And 'the change of x at different moments' can in turn be extended to mean 'motion.' In other words, this topic is asking, 'How does motion occur?' 'What is its basis?' 'How do we know where it should go the next moment?'"

Blade Tusk was not a teacher by trade. Judging the difficulty and precision of the material was still somewhat difficult for him.

At this moment, he could only do his best to recount the knowledge in his mind in ways he felt were easy to understand.

In any case, after one lesson, it was still hard to say how effective it had been. Some of the little ones stared blankly, seemingly understanding nothing at all, while others appeared deep in thought.

"Old Witch Doctor, what did you think?"

After class, Blade Tusk ran into Old Witch Doctor, who had been listening from a corner the entire time, and asked him.

"It was very enlightening, especially that part about 'grasping the arrangement of elements in space.' The way we use magic now—do you think it might also be explained through this?"

"Mm, I've had similar thoughts. But as I told you before, our means of observing the 'microscopic world' are far too lacking. For now, we can only categorize it as a 'hypothesis.'"

"Mm, being cautious is a good thing. Still, it seemed not many of the children understood. Was the content too advanced?"

"It can't be helped. The age range is too broad, so differences in comprehension are normal. Besides, I'm not asking them all to understand it. Our ship is small, so it turns quickly—we'll teach at this pace for a while first, then organize an 'exam' later. Depending on the results, we can decide whether to split them into different tracks or simply lower the difficulty."

"That works too. When the time comes, we can pick out a group of those who learn well and cultivate them first."

"Certainly. For the next lesson, I plan to formally start teaching them with 'uniform linear motion.'"

"Fine, you handle it as you see fit. But don't slack off on your own research either. If you need anything, come find us three old fellows anytime."

"Alright."

After a brief exchange, the two Trolls went their separate ways.

Returning to the "laboratory," Blade Tusk began his research once more.

All the various "simple" storage methods he had tried before had been declared failures in development.

This time, he planned to bring out something he had instinctively dismissed even earlier due to lacking the necessary conditions—energy, metal, and so on.

Let's first sort out how refrigerators worked in my previous life. No electricity, no metal ore, no means of processing. Even if I figure it out, it may not be much use. Still, hopefully it can at least broaden my thinking.

With that in mind, he began trying to recall the structure of the refrigerator his family had owned when he was little.

It seems old-fashioned refrigerators all had a metal grille on the back that gave off heat. Thinking of that together with the low temperature inside the refrigerator, the working principle seems easy enough to deduce.

It transferred the heat from inside to the grille by some means, then dispersed it. That should be right, shouldn't it?

Was it called heat exchange? Or did it have some other name?

Mm, the name isn't important. First, think about how the heat is transferred.

Heat dissipation... For the human body, part of its heat dissipation should happen through the evaporation of sweat, right?

Applied to a refrigerator, that would mean the cooling area absorbs heat while the heat-dissipation area releases it. If evaporating water can carry away the body's heat, then evaporation should take place in the cooling area, not in the heat-dissipation area I instinctively thought of.

From this, it can be deduced that what flows into the cooling area should be a low-temperature liquid, making it easier to carry away heat.

Liquids absorb heat when they evaporate—that is a phenomenon, right? So perhaps it isn't necessarily carrying heat away. Maybe the conversion process itself consumes heat. For now, it's enough to know the result works that way.

But how could it evaporate at low temperatures?

Let me think. Is there some principle involved? At high altitudes, water's boiling point drops. The key seems to be low pressure?

In other words, what flows into the cooling area might be a low-temperature, low-pressure liquid.

By making it evaporate in the cooling area, it carries away—or consumes—the heat?

Then what flows out of the cooling area is low-pressure vapor? What about its temperature? The cooling area isn't a furnace. Whether it carries away heat or consumes heat, I don't feel its temperature should rise all that much.

Then where does the heat released by the radiator come from?

Let's assume the radiator's heat has nothing to do with the temperature carried out of the cooling area. Based on that premise, where would the outgoing low-pressure vapor have to go to make sense?

First, the refrigerator has no external liquid inlet—which means the substance inside... I think it was called "refrigerant," right?

That means the refrigerant inside is recycled. In other words, the low-temperature, low-pressure liquid flowing into the cooling area and the low-pressure gas flowing out of it come from the same source.

Then it must go through one or several processes before it can be used again.

Let me think. Gas into liquid. Pressure? Compressing the vapor? If that's it... if liquid turning into gas absorbs heat, then wouldn't gas turning into liquid do the opposite and release heat? Low-temperature, low-pressure vapor is compressed into a high-temperature, high-pressure liquid.

So the radiator is actually dispersing the heat released when refrigerant vapor is compressed into liquid? Mm, that makes much more sense.

Let's call the place where the vapor is compressed the compression zone for now.

Let's organize this: compression zone—becomes high-temperature, high-pressure liquid—heat-dissipation zone—becomes low-temperature, low-pressure liquid—cooling zone—becomes low-temperature, low-pressure gas—compression zone. And so the cycle repeats.

No, the gap between a high-temperature, high-pressure liquid and a low-temperature, low-pressure liquid is too great. The heat-dissipation zone shouldn't be capable of that. So there should be another step in between.

That step should serve to lower both temperature and pressure.

When pressure drops, a liquid's boiling point falls. When the boiling point falls, it evaporates more easily. Evaporation consumes heat, which naturally lowers the temperature. So, low pressure = easy evaporation = cooling. Does that mean I only need to consider how to lower the pressure?

Lower the pressure.