Chapter 75 - 59: Pressure
Four o’clock in the afternoon.
The sky over Jinling was still bright.
Sunlight slanted through the glass windows of the third-floor corridor of the administration building, spilling into the small lecture hall.
The classroom was quiet.
Only the air conditioner in the corner blew out a cool breeze.
It stirred the stuffy air with a monotonous hum.
On the blackboard,
a diagram of a DC motor lifting a suspended weight, drawn with a few simple chalk lines, remained quietly in place.
Labeled beside it were U, R, and m.
Professor Wang sat on a wooden chair behind the teacher’s desk.
He cupped a chipped enamel mug printed with the words "Labor is Glorious."
He wasn’t looking at the students below, his gaze fixed on the few tea leaves floating in his mug.
He would occasionally blow on the surface before taking a sip.
Below the lectern,
six junior high students were scattered across the first two rows of the lecture hall.
The thirty-minute countdown was like an invisible hand, slowly tightening its grip on the air in the room.
Wang Huashao sat in the second row.
The black pen in his hand flew across the scratch paper.
He wrote down a formula.
He paused.
His brows were furrowed so tightly they almost formed a knot.
Then, he forcefully crossed out the formula.
The tip of his pen left a deep black mark on the paper, nearly tearing through it.
He wanted to use Ohm’s law.
It was the most fundamental, core law of electricity in junior high physics.
But Professor Wang’s earlier words were like a bucket of cold water.
A motor burns out when it stalls, but not when it’s running.
If you just used Ohm’s law, the current would be constant, and so would the heat generated.
That couldn’t explain the huge difference in heat production between a running motor and a stalled one.
Wang Huashao ran a hand through his short hair in frustration.
’My brain is a tangled mess,’ he thought, ’and I can’t find a single thread to pull.’
To his right sat Miao Shian.
The collar of his white shirt was already slightly damp with sweat.
Behind his gold-rimmed glasses, his eyes were glued to the diagram on the board.
His scratch paper was filled with equations for energy conversion.
Electrical energy, mechanical energy, internal energy.
He realized the energy wasn’t going to just one place.
But he was stuck on a critical point.
He didn’t know how to express the back electromotive force—generated by the motor’s internal coils cutting through magnetic field lines—as an algebraic formula.
His pen hovered over the paper, hesitating to fall.
In the corner by the window,
He Gui gripped his pen tightly.
His palms were sweaty, making his grip stiff.
He looked at the half-page of calculations he’d written, all based on derivations in an ideal state.
He silently turned the page and started over.
Zhou Kai held a Parker fountain pen.
The fountain pen glided across the paper, leaving behind strings of complex mathematical derivations.
He had discovered the limitations of the physics formulas and was trying to use his formidable mathematical skills to brute-force a micro-element model to solve for the velocity, v.
His calculation speed was extremely fast.
But every time he reached the end of a derivation, the units wouldn’t unify.
He’d either have an extra ampere or be missing a volt.
The only sounds in the classroom were the scratching of pens on paper,
and the occasional soft rustle of a turning page.
Time ticked by, second by second.
The angle of the sun outside grew lower, and the light in the classroom slowly turned a warmer yellow.
Lin Yi sat right in the center of the front row.
She hadn’t drawn any force-body diagrams on her scratch paper at all.
One hand supported her chin, while the other tapped a perfectly steady rhythm on the desktop.
TAP, TAP, TAP.
The sound was very light, as if she were humming an unknown pop song in her head.
She stared at the exceedingly simple motor diagram on the blackboard.
She looked at it for about five minutes.
"Tch."
Lin Yi muttered under her breath.
"The old guy really knows how to set a trap."
She finally deigned to sit up straight and gave a huge stretch.
Then, she grabbed the black gel pen on her desk.
The pen tip landed on the white paper.
There were no corrections whatsoever.
Her handwriting was a bit flamboyant and wild, but her logic was exceptionally clear.
She hadn’t bothered with any complex expressions for back EMF, nor had she agonized over how the current changed.
’That’s all just beating around the bush.’
Energy conservation.
’It’s so simple.’
The electrical energy from the power source is partly converted into internal energy as the coil heats up, and the rest is all used to do mechanical work by lifting the block.
Lin Yi wrote out the lines of equations on her paper with extreme fluency.
After writing down this core equation,
she didn’t pause.
The gel pen skated across the paper with incredible speed.
She needed to find the maximum velocity, v.
Rearrange the equation to get a quadratic equation in terms of current I.
Complete the square, find the extreme value.
Less than three minutes.
Three incredibly clean lines of algebraic expressions.
Lin Yi drew two casual horizontal lines under the answer.
"Done,"
she mumbled, her voice tinged with a mix of ease and pride.
Then, she picked up the cap.
CLICK.
The cap snapped onto the pen.
Less than ten minutes had passed.
Lin Yi pushed her notepad forward.
She slumped back into her chair, crossed her arms, and began to count the cracks in the ceiling out of boredom.
Chen Zhuo, sitting diagonally behind her,
heard the soft click of the pen being capped.
His own movements were not affected in the slightest.
Chen Zhuo’s scratch paper was the complete opposite of Lin Yi’s, which had been mostly blank.
His page was densely packed with writing.
He didn’t have Lin Yi’s ethereal intuition that could see through to the physical essence of a problem in a single glance.
His method of problem-solving was an extremely solid, extremely rigorous form of brute-force deconstruction.
With the pen in his hand, he had drawn a complete equivalent circuit diagram.
He isolated the motor’s internal coil resistance.
He added a virtual power source in series within the circuit to represent the back EMF.
Beside it, he used the most basic mechanics formulas to denote the force equilibrium when the weight was rising at a constant velocity.
He took an extremely complex, dynamic process,
and, like dismantling a mechanical clock, broke it down into its most basic, indisputable components.
Then, using a tight chain of logic, he meshed these components back together.
Electrical work W = UIt.
Joule heating Q = I²Rt.
Mechanical work E = mgvt.
He listed the three independent formulas.
Solved them simultaneously.
Eliminated the time variable, t.
The ink rubbed against the white paper.
Chen Zhuo drew the final fraction bar.
He wrote down the final algebraic expression.
His answer was identical in its final form to Lin Yi’s.
Different paths, same destination.
Chen Zhuo put down his pen.
It made a faint clatter as it touched the wooden desk.
After Lin Yi had put down her pen,
less than forty seconds had passed.
Two small sounds.
Two completed answer sheets.
Not one of the other four boys sitting nearby looked up.
But their writing movements had clearly become somewhat stiff.
The air in the classroom seemed to grow even thicker.
An invisible, immense psychological gap fell upon them, like a stone pressing on their chests.
They were all the top students from their respective cities.
Geniuses in the eyes of their teachers, freaks in the eyes of their classmates.
But now, on this ordinary afternoon,
in just ten minutes,
the unseen chasm called talent and foundation had opened up right before them.