Soon, the bell rang again. This class was physics.
Liu Limin hadn’t returned yet, so Li Dong remained in his seat at the very back of the classroom.
After the "crushing" experience of the last biology class, he now felt a flicker of anticipation.
He was eager to see just how interesting a physics class at Jiangcheng’s top high school could be.
After all, he could already foresee a bottleneck in his physics abilities.
Problems he knew how to do couldn’t stop him, but for the ones he didn’t, he needed to fill in the gaps in his chain of knowledge. This was a systematic undertaking; without a guide, he might manage on his own, but he would take many detours.
’I’m so looking forward to this...’
Just then, an old teacher with graying hair and glasses walked up to the podium.
Chen Ke, the rock of the Jiangcheng Sixth Middle School physics department, and the renowned former head coach of the provincial Physics Ossai team.
Twenty-two national final gold medals, one international Ossai gold medal, and countless domestic competition awards—this was the track record of his coaching career.
"Class, today we’re going to play a fun little game."
Elder Chen placed his thermos on the podium, a kind and affable smile on his face.
However, upon seeing this smile, the students of the elite class below shuddered.
Last month, Qin Yan—the top student in the school, who had already won a gold medal in the national finals and secured a spot on the national training team—had fallen victim to that same "affable smile." He had been stumped by a single problem for an entire class period, and his face was green by the time the bell rang.
’This old coot is definitely up to something again!’
Elder Chen ignored the resentful gazes from his students. He picked up a piece of chalk, turned to the blackboard, and began to write as he spoke.
"We’re going to break down a comprehensive problem on rigid body dynamics. It’s adapted from a real question from last year’s IPhO and was also used as a placement test for this year’s national training camp."
As soon as he said this, the students in the classroom all had expressions that said, ’Just as I thought’.
They were used to doing real Ossai problems, but the killer was in the word "adapted."
This old fellow loved to devilishly modify problems. He would often just change one condition, which didn’t necessarily increase the difficulty much, but it made the angle of approach extremely tricky.
But Li Dong, sitting in the back row, was so excited that he adjusted his posture, preparing to welcome a thrilling mental storm.
[As shown in the figure, a uniform solid sphere of mass M and radius R is initially spinning at a high angular velocity ω0 about a horizontal axis of symmetry. At the same time, its center of mass is translating to the right along a rough horizontal surface with an initial velocity v0. The coefficient of sliding friction between the sphere and the surface is μ.]
Find the time t required for the sphere to go from its initial state to a state of pure rolling, and the center-of-mass velocity v during pure rolling.
If the horizontal surface is not perfectly rigid, and the rolling sphere forms a circular contact patch of radius a, with a rolling friction coefficient of δ, find the total distance L traveled by the center of mass before the sphere finally stops rolling.
[If the sphere’s initial axis of rotation is tilted at an angle θ with respect to the vertical, consider the precession effect caused by the gravitational torque. Qualitatively analyze the change in the sphere’s rolling trajectory and derive the expression for the precession angular velocity Ω.]
"Go on, pick up your pens and start calculating. It’s not difficult."
Elder Chen tossed the chalk down and said with a chuckle.
Li Dong, sitting below, finished reading the problem carefully and nodded in deep agreement.
’It really isn’t difficult. This teacher is quite honest.’
Just a moment ago, the entire logical derivation had already run through Li Dong’s mind.
He uncapped his pen and began to write on his scratch paper:
"First question. The moment of inertia about the center of mass is J = 2/5 MR2. The sliding friction force is f = μMg. The acceleration of the center of mass is a = -f/M = -μg... Angular momentum is conserved about the contact point because the torque of the friction force about that point is zero. Therefore, the initial angular momentum Jω0 + Mv0R = Jω + MvR. Combining this with the pure rolling condition v = ωR, we can solve for v and t..."
Simply put, the first question was a standard pure rolling problem, at most the level of a mid-tier question in the Huaxuan Cup semifinals.
The second question was a rolling friction problem involving a circular contact patch, which just introduced a differential integration for the resistive torque.
You just had to perform an integration, calculate the resistive torque, and then apply the work-energy theorem. It was a tiny bit harder than the first question, but that’s all.
As for the third question...
Others might find the precession effect to be the most difficult, but Li Dong thought it was the easiest part.
A precession problem? What a joke! Just a few days ago, under the guise of the "foolish nephew," he had been in the group chat discussing the precession of Mercury’s perihelion and celestial orbital perturbations with Levay and Newton!
Compared to problems of that caliber, rigid body precession within the framework of Classical Mechanics was practically child’s play.
This problem didn’t even involve nutation; it was purely a test of M = dL/dt.
Li Dong spent about three to four minutes writing down the final expressions for all three questions on his scratch paper, and even drew a free-body diagram for the precessing trajectory on the side.
Done.
Li Dong put down his pen and looked up at the students around him.
He saw the star students of Sixth Middle School’s elite class frowning and pulling at their hair.
Seeing their expressions, Li Dong mused to himself.
’Looks like I’m a bit better than them at physics. They’ll probably be calculating for a while longer.’
Li Dong completely overlooked one possibility: that this group of star students might not be able to solve it at all.
With time on his hands and not wanting to waste it, this student—on his very first day at Sixth Middle School—started playing on his phone during his first physics class...
Up at the podium, Elder Chen had been watching with an amused chuckle, his hands behind his back, as this group of usually arrogant geniuses scratched their heads in distress.
Suddenly, he noticed Li Dong in the corner of the classroom.
Elder Chen narrowed his eyes slightly.
This student looked a bit unfamiliar, but the elite class had a fluid roster, so it was normal not to have seen him before.
But what Elder Chen found strange wasn’t the unfamiliar face, but the fact that this student... was looking down and playing on his phone?
In all his years teaching at Sixth Middle School, Old Chen hadn’t seen such an audacious young man in a long time.
But he didn’t get angry.
Because anyone who could get into the elite class was definitely not the type of bad student who had given up on themselves.
If it wasn’t that he didn’t want to learn, then there was only one other possibility—he was finished.
Elder Chen subconsciously glanced at the time.
A little over five minutes.
And from the looks of it, the kid had probably been playing for a little while already.
He had given this problem to Qin Yan before, and it had taken Qin Yan seven minutes to arrive at the correct analytical expression for the third question.
’This kid... finished in less than five minutes?’
’I wonder if he even got it right.’
He slowly walked down from the podium and strolled toward the back of the classroom.
Lately, the great Newton had been on an absolute tear during his Second Industrial Revolution.
[Isaac Newton]: Everyone, my improvements to the internal combustion engine have been a great success. The stability of the four-stroke cycle far exceeds expectations. The high-pressure steam engine is also mature, and we have already applied it to deep-level water pumping in mines and to initial railway transport tracks!
[Isaac Newton]: Our industrialization process is exploding at a geometric rate!
Even through the screen, Li Dong could feel the proud arrogance of a man who held the pulse of an era in his hands.
But then...
[Isaac Newton]: However, I have encountered an extremely difficult problem.
[Isaac Newton]: We’re out of people...
Li Dong read Newton’s message and suddenly noticed a terrifying detail.
[Isaac Newton]: Our current world population is just over ten million! And the vast majority are concentrated in the city-states within the sphere of influence of the Royal Academy of Sciences. The world outside is still an uncivilized wasteland!
[Isaac Newton]: With large numbers of farm laborers being drafted into factories, our food production is plummeting! But if we don’t have enough food to fill the workers’ stomachs, all those great machines will eventually become nothing but a pile of scrap iron!
’Just over ten million people?!’
Li Dong stared at those words, his heart sinking with shock.
This was definitely not the 17th-century Earth he knew!
From the sound of it, Newton’s world seemed to have no concept of nations at all. Was it a "Scientific Utopia" completely dominated by the "Royal Academy of Sciences"?
’So this is the state of parallel universe number 1666...’
Li Dong swallowed. Though he was shocked by the social structure of that other world, the moment "food production" was mentioned, he immediately recalled the knowledge from his last biology class.
[FinalsGrinder]: @Isaac Newton, Sir Newton, regarding the issue of food production, I have a somewhat underdeveloped suggestion.
[FinalsGrinder]: We can utilize the "hybrid vigor" between different plant lines to find specific mutant strains and establish "male sterile lines," "maintainer lines," and "restorer lines." As long as these three lines are operational, mass breeding of superior varieties can be achieved, and doubling the food production will definitely not be a dream!
[Isaac Newton]: ???
[Isaac Newton]: Your Excellency FinalsGrinder, I have heard of this "hybrid vigor" you speak of. Horticulturists can indeed breed more robust crops through hybridization, but no one can explain the principles behind it, let alone achieve stable, large-scale breeding!
[Isaac Newton]: Taking a huge step back, even if they can be hybridized, how is this advantage passed on to the next generation? Is it mixed together like fluids? And what is this absurd concept of a "sterile line"?
Newton was completely baffled.
In Newton’s universe, number 1666, Classical Mechanics may have reached its zenith a century early, but biology was likely still in an extremely primitive and unenlightened stage.
Reading Newton’s questions, Li Dong was also at a loss for a moment.
Although he had just forcibly derived the basic framework of cytoplasmic-nuclear interaction (S-rr) in biology class and knew how to solve problems with it... but knowing how to solve a problem and explaining it to a 17th-century god of physics were two completely different things.
Just as Li Dong was wondering how to use simple, easy-to-understand language to give these great minds a biology lesson...
...a group member suddenly surfaced.
[It is not absurd, Sir Newton.]
Li Dong paused for a moment, then looked at the person’s ID.
[Gregor John Mendel]
It was him!
The man who made countless high school students go cross-eyed calculating the probabilities of red flowers and white flowers, tall stems and short stems, yellow and round versus green and wrinkled peas!
The True God of biology—Mendel!

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