Chapter 40
“The Equation That Moves a River”
(Kai and Rutia’s Summer Vacation Arc – Part IX)
The next morning.
The villagers gathered along the riverbank, hoes and pickaxes in hand.
Kai stood before them, propping up a large wooden board and running white chalk across it in quick strokes of numbers and symbols.
“First, the distance from the river to the village—it’s just over two hundred meters in a straight line.
Next, the slope we need… tan θ = height ÷ distance.
Calculating that, the gradient should be about three degrees for the water to flow naturally.”
The farmers gaped at him, mouths open. Eventually, one of them muttered,
“…Three degrees means…”
“That if the difference in height between the village square and the river’s surface is this much, the water will flow down!”
Kai grinned.
“Exactly. Now all we gotta do is dig the trench without messing up the angle.”
Wilhelm slung his hoe over his shoulder and rolled his arms.
“I see. Then we shall take the lead.”
“You too, Brother?!” Rutia exclaimed in surprise.
Julius laughed lightly.
“Sister, this is a battle to save our people. We’ll just be swinging hoes instead of swords.”
At those words, the villagers’ spirits soared.
“Even the lord’s sons are helping!”
“Then we can’t fall behind!”
Kai began shouting directions like a foreman.
“That team—dig in a straight line! If you go past three degrees, the water’ll rush too fast and collapse the trench!
You guys over there, remove those big rocks! F = ma—force equals mass times acceleration! Push together and it’ll feel lighter!”
The villagers laughed while working hard, sweat streaming down their faces.
Beside them, Rutia watched proudly from under her parasol.
“Kai—no, my husband. You’re truly leading this land.”
“Leading? Naw, it’s just a bit of math in action!”
“And with that math, you’ve saved a village. That makes you my husband indeed!”
“No activating the ‘wife mode’ right now!”
After several days of work, the earthen canal finally reached the village.
For the finishing touch, they broke open part of the riverbank and let the water in.
With a roaring sound, the water rushed down the trench, and a brand-new stream came to life in the village square.
“Oooohhh!”
“The water—it’s coming! The water’s here!!”
The villagers cheered, and the children kicked off their shoes and splashed into the cool stream.
The old village chief spoke, his voice trembling.
“Sir Son-in-Law… you have saved this village. You are the savior of our lives.”
“Nah,” Kai said, scratching his head. “All I did was crunch some numbers. You all did the digging.”
But the villagers shook their heads.
“No. You guided us.”
“Thank you, Sir Son-in-Law!”
“Stop calling me Sir Son-in-Law already!!!”
Rutia wrapped her arm around Kai’s shoulder, smiling radiantly.
“Did you hear that, my dear husband? Even to the villagers, you’re now my husband.”
“Stop calling me wife!”
Laughter and cheers echoed through the summer sky.
