Chapter 131 Newton: So love will disappear, right?
In front of the blackboard.
After listening to Xu Yun's words, Lao Su bent down slightly, picked up a pebble from beside him, picked it up and let go.
Just listen to a click.
The pebbles fell back to the ground naturally.
"gravity"
Then Lao Su repeated the word with a thoughtful expression.
"The name is quite interesting, but Xiao Wang, how should we explain this heavy word "gravity"?"
Xu Yun thought for a moment and said the answer he had prepared long ago.
"The heavy word gravity means the weight of an object.
That is to say, any object with mass, no matter how small it is, will produce gravity."
Old Su nodded slightly, replaced the stones with grains of sand in his mind, and then continued to ask
"So Xiao Wang, where does gravity come from?"
Hearing this question, Xu Yun paused for a moment, and the expression on his face became a little more solemn.
"It is rumored that a long time ago, Fengling Yueying Sect gave birth to a sage named Shi Hao, who was extremely intelligent since he was a child.
He discovered that among all things in the world, every object with mass exerts a force on other objects with mass.
He named this force universal gravitation, and gravity is a component of gravity on the earth, causing all objects to fall freely after being separated from support."
Having said this.
Xu Yun couldn't help but look at Lao Su, fearing that the boss would ask again, "What is the nature of gravity?"
After all, the nature of gravitation is a concept that has never been concretely determined by later generations.
As we all know.
Although Maverick discovered gravity, what he discovered was actually the mathematical definition of gravity, not the physical concept of gravity.
The answer to physical concepts will have to wait until Einstein proposes the theory of relativity, and the physics community will gain further understanding of universal gravitation.
The essence of universal gravity is the curvature of space—or in other words, it is not just space that is curved, but the four-dimensional space-time.
For the theory of relativity.
Space-time is a whole,&bsp&bspDescribed in terms of physics,&bsp&bspFlat space-time is called "Minkowski space".
The meaning of curvature is that the metric of the straight Minkowski space has changed.
at the same time.
General relativity believes that&bsp&bspIt is the quality of matter that causes space-time to curve, and objects move along the shortest path of four-dimensional space-time (geodesic motion),&bsp&bspThe form of their motion is represented by universal gravitation.
Let’s take Xu Yun as an example.
Xu Yun landed.
Maverick said, this is because the gravity of the earth pulled Xu Yun to the ground.
Einstein said no, it was the mass of the Earth that caused the four-dimensional space-time around the Earth to curve,&bsp&bspThat's why Xu Yun fell.
Xu Yun (called test particle in physics terminology) fell from the tree. From the perspective of four-dimensional space-time, Xu Yun walked the shortest distance from a certain point on the tree at a certain time to a certain point on the ground at a certain time.
That is to say, Xu Yun is moving according to the four-dimensional geodesic.
The projection of this four-dimensional geodesic motion in the three-dimensional space is the trajectory of Xu Yun falling from the tree.
Therefore, in later generations, the explanations of universal gravitation in the three mechanics are also completely different.
In Maverick's classical mechanics, gravity is considered to be a basic force generated by mass.
Einstein's general theory of relativity believes that gravity is caused by the curvature of space-time.
Quantum mechanics believes that gravity is caused by the exchange of gravitons between matter.
It is unknown whether the above views are right or wrong, and they are still being debated today - "siee" classified this issue as one of the most challenging scientific issues on the occasion of its founding anniversary.
That's right.
Just like bicycles, it is an issue that will be mentioned in junior high school physics.&bsp&bspToday's scientific community still has no specific conclusion.
At the above three o'clock,&bsp&bspclassical mechanics' qualitative range of gravity is relatively limited, and in many cases classical mechanics is not even used.
Therefore, some people always claim that general relativity denies classical mechanics. This is actually a very rogue statement.
Even in a novel written by Xu Yun in his previous life, the protagonist met Mavericks in time travel, but some people commented, "Why are you looking for Newton? Classical mechanics is nonsense."
Actually.
The way to judge whether classical mechanics is correct is actually very simple - just see whether it has practical value.
It allows you to build airplanes, drive tanks, build tens or even hundreds of meters tall buildings, and dive deep into the water.
It can be used in various fields of our macro world, so it is very successful.
At least in the macroscopic world we can see now, you can absolutely believe it.
Do you remember that pendulum experiment?
Change the pendulum into a beheading knife and let it go.
Do you dare to raise the neck to its original position and raise it one centimeter higher?
Anyway, Xu Yun dared to do it, and he actually did it, but he used an iron ball as big as a human head.
Compared with classical mechanics, relativity and quantum mechanics discuss a broader category.
That is to say, in the high-speed microscopic world, everything happens to the power of ten, so classical mechanics is not easy to use.
all in all.
Each of the three has its own applicable fields,&bsp&bspClassical physics is still strong and necessary in life.
Considering that during the Northern Song Dynasty, it might be possible to understand the microscopic world, but what about the theory of relativity and quantum mechanics?
Unless Old Su could recite poetry until he was 130 years old, it would be impossible.
Therefore, Xu Yun’s idea is to discuss gravity within the category of classical mechanics, and all knowledge will be taught according to the basic framework of classical mechanics.
His eyes returned to reality.
Maybe it's because I don't have an intuitive concept of gravity.
This chapter is not finished yet, please click on the next page to continue reading the exciting content! After listening to Xu Yun’s explanation, Lao Su did not delve into the origin of this ‘force’ in depth.
Instead, there was a new wave of doubt.
I saw him open his palm, put it next to Xiao Zhao and wave it, then looked at Xu Yun
"Xiao Wang, according to what you said, there will be a gravitational force between objects.
So why are Xiao Zhao and Xiao Li so close to each other and not aware of any attraction at all?"
Xu Yun looked up at Xiao Li and Xiao Zhao who were a little confused, and explained with a smile
"Sir, gravitation is the weakest force in the world. It is even lower than the bite of a mosquito in summer, so it is normal that you cannot feel it."
Hearing Xu Yun's words, Lao Su didn't respond yet, and Xiao Zhao, who had been silent until now, couldn't help but speak.
"Your Majesty, since this so-called 'gravity' is too small to be detected, how do you know that it actually exists?"
Xu Yun immediately cast an approving look at the admirer, then he pointed at a assembled simple prop beside him and said
"Of course it depends on this."
This set of props is about 40 to 50 centimeters tall and was also made using tools found by Mr. Xie Duguan.
When Lao Su was experimenting with chalk, Xu Yun was tinkering with this thing.
And since it can be assembled in a short time, the materials used for this prop are naturally not that complicated.
The main body of the prop is a torsion scale that is different from later generations, but has similar functions - yes, a torsion scale
The prototype of the modern torsion scale was produced by Father Michael of the Royal Society in the 19th century, but before that, various ancient civilizations had some relatively primitive torsion scales.
For example, the torsion scale invented by Lao Su in the Song Dynasty.
When I was supervising the production of a water transport instrument platform, in order to calculate the torque, I designed a classical torsion scale that could be precisely calibrated.
The tool diagram was also drawn by Lao Su in "Shao Sheng Yi Xiang Fa Yao".
And at this moment.
This torsion scale is tied to the bracket through a very tough steel wire, and two iron balls, one large and one small, are placed at both ends of the torsion scale.
There is a small mirror on the steel wire that is not very accurate, but can reflect normally.
That's right.
See here.
The students who were not mad at the physics teacher must have guessed it.
The experiment Xu Yun will conduct this time will be famous in later generations.