A few days after the visit, the 1978 class of the Department of Physics officially began studying the core professional course "Mechanics".
The lecturer is an old professor named Sun, who is rigorous in his research and has very high requirements.
That morning, after Professor Sun finished explaining the moment of inertia of rigid bodies, he wrote a comprehensive application problem on the blackboard:
A homogeneous circular disk of mass m and radius R can be rotated about a smooth horizontal axis passing through its center and perpendicular to the disk. A light rope is wound around the disk, and a weight of mass M is suspended from the end of the rope.
Initially, the system is at rest, and the weight is at a height h from the disk. Calculate the angular velocity ω of the disk when the weight falls from a height h.
The title is quite biased, but it integrates multiple knowledge points such as Newton's first law, law of rotation, conservation of energy, etc.
Professor Sun looked around the classroom and asked, "Who would like to try to analyze the thinking behind this question?"
The classroom became quiet for a moment.
Chen Peng frowned as he drew a force diagram on paper, Li Wei bit the pen while thinking, and Zhou Zhe pushed his glasses, seemingly doing rapid mental arithmetic.
Just as everyone was still digesting the question, a cold voice sounded, with a deliberate calmness and condescending tone:
"Professor, the idea behind this question is very clear."
Everyone looked in the direction of the voice and saw Zhao Rui.
He stood up, but glanced at Lu Qingyang who was sitting far away with a half-smile in his eyes, his eyes full of provocation.
Zhao Rui completed the task in one go, his deduction was smooth and his answer was accurate.
He raised his chin slightly and looked at Professor Sun, but his eyes were fixed on Lu Qingyang, with a barely perceptible sarcasm on the corner of his mouth.
Professor Sun nodded and said, "Student Zhao Rui's thinking and deduction are very correct and standard. Very good. Please take a seat."
Zhao Rui sat down, and a low murmur of discussion was heard in the classroom.
Everyone thought Zhao Rui was really good, but they also felt that the way he stood up to solve the problem just now was a bit boastful.
Professor Sun looked at everyone and said, "Zhao Rui solved this problem perfectly. The charm of physics lies in the diversity of ideas. Does anyone else have similar ideas or would like to add something?"
At this time, Lu Qingyang calmly raised his hand.
Zhao Rui stared at him with the intention of watching a good show.
"Student Lu Qingyang, please speak." Professor Sun gestured.
Lu Qingyang stood up, but did not solve the problem immediately. Instead, he looked at the question on the blackboard and asked a question that seemed unrelated to the solution:
"Professor Sun, I'd like to ask you a question. The question mentions a 'smooth horizontal axis.' In actual mechanical structures, such as drive shafts or flywheels in factories, is there really such a thing as absolute 'smoothness'? The friction coefficient μ of bearings is usually zero. So, if bearing friction is taken into account, how should the motion range and final angular velocity ω of this system be corrected?"
As soon as Lu Qingyang asked the question, the classroom became quiet instantly!
It directly brings an idealized physical model back to the real world full of friction.
This is the most common problem encountered when machinery is running in the factory - friction loss!
The smug look on Zhao Rui's face froze instantly, replaced by a hint of anger.
Just after perfectly demonstrating his problem-solving skills, Lu Qingyang suddenly took matters into his own hands and questioned the assumptions and premises of the question? This was a blatant provocation!
Professor Sun was stunned for a moment, then his eyes burst with strong interest:
"Good question, Mr. Lu Qingyang, this is a very practical one! In ideal models, we ignore friction, but in real applications, friction is often a key factor that must be considered!"
놛 turned to the blackboard, picked up the chalk, and began to write quickly.
Professor Sun finished writing, put down the chalk, and looked at Lu Qingyang approvingly:
"Lu Qingyang's question reminds us that physical models simplify reality, but engineers must consider various real-world factors when applying them, such as friction, air resistance, material deformation, and so on.
Zhao Rui provided a perfect answer to this question under ideal circumstances, while Lu Qingyang pointed out the key points for extending it to practical applications. Both approaches are important.
Lu Qingyang was not unaware of Zhao Rui's sullen face and eyes that were about to explode.
At this moment, what occupied 놛놅's mind was the lunch box that Aunt Liu stuffed into 놛놅's hand when she went out in the morning.
Ever since he had experienced the bland cabbage soup and the almost transparent tofu soup in the cafeteria last time, Lu Qingyang decided not to wrong his stomach again.
With Aunt Liu, a chef whose cooking skills are constantly improving, and space, a natural heat preservation artifact, at home, why would you bother with those tasteless cafeteria dishes?
It's such a waste!
During the lunch break, most people flocked to the cafeteria or library. Lu Qingyang turned around and did not follow the crowd, but walked towards a relatively secluded place behind the physics building.
There is an abandoned flower bed covered with vines, and next to it is an old boiler room converted into a warehouse. Usually, there are few people coming here.
After confirming that there was no one around, Lu Qingyang walked to the shady base of the warehouse wall, where there were several scattered bluestone slabs.
With a slight movement of his mind, his consciousness sank into space, and a warm lunch box appeared out of thin air in his hand.
This is one of the most practical aspects of space: the flow of time stands still.
The food was still steaming hot when I put it in the morning, and when I took it out now, it still kept the temperature as if it had just been taken out of the pot.
Lu Qingyang opened the lunch box lid with a smile, and an alluring aroma instantly filled the air. The lunch box was filled with layers of food:
There are braised pork and shredded pork with Beijing sauce in the lunch box.
Aunt Liu has mastered the skill of “stir-frying sugar color”. The meat is fat and lean, stewed until it is tender and tasty, with a rich sauce and an attractive luster.
Stir-fried seasonal vegetables, fresh cabbage, which is rare in late autumn, is juicy and green, stir-fried with garlic, with a wok aroma, and scrambled eggs with cucumber.
There is also white rice with plump grains and steamed to perfection, which is now emitting steaming hot.
He took out his chopsticks and impatiently picked up a piece of trembling braised pork and put it into his mouth.
The fat melts in your mouth, the lean meat is crispy and tender, and the rich aroma of the sauce mixed with a slight sweetness explodes on the tip of your tongue.
Add some garlic-fried cabbage for a refreshing and greasy taste.
Finally, take a big mouthful of warm rice. The aroma of rice mixed with the aroma of gravy and vegetables, the warmth and soothing feeling goes from the throat all the way down to the stomach.
I sat on the stone slab, leaning against the mottled wall, enjoying this moment of tranquility.
The sun shone through the gaps between the sparse vines, casting a few spots of light. In the distance, the sound of people bustling about in the cafeteria and the sound of inspiring songs being played on the campus radio could be faintly heard.
"Hmm... Aunt Liu's cooking skills are really getting better and better." Lu Qingyang murmured to himself in satisfaction as he devoured the meal.
I remember that when I left home this morning, Aunt Liu had specifically reminded me, "Qingyang, studying takes a lot of brain power, so eat more! If you're tired, I'll make it for you when I get back tonight!"
Just as we were immersed in the enjoyment of delicious food, we seemed to hear footsteps and voices on the road in the distance.
Lu Qingyang immediately became alert and quickly covered the lunch box. With a thought, the lunch box and chopsticks disappeared instantly and returned to the space.
He stood up as if nothing had happened, brushed off the dust on his pants, and still chewed the last bite of the delicious and glutinous braised pork with relish.
The rich aroma of the sauce seems to still linger between the lips and teeth.
At this moment, a deliberately suppressed argument was heard from the corner of the road in the distance.
The footsteps came from far away.
"I've said it so many times, I like you, you're pestering me!" A female voice rang out.
"I've been chasing you for so long and put in so much effort, and you treat me like this?" A male voice sounded immediately afterwards.
Lu Qingyang looked in the direction of the sound and saw a man and a woman turning from the road.
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