Into Unscientific

In front of the blackboard.

After listening to Xu Yun's words.

Old Su bent down slightly, picked up a small stone from his side, and let go of it after picking it up.

Just a click.

The stone 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 to explain this heavy word that does not know gravity?"

Xu Yun thought for a moment, and said the answer he had prepared a long time ago:

"The heavy word for gravity means the weight of an object.

That is to say, any object with mass, no matter how small it is, will generate gravity accordingly. "

Old Su's eyes went blank, and he replaced stones with sand grains in his mind for a simulation.

After accepting this concept, he continued to ask:

"Then Xiao Wang, where does gravity come from?"

Hearing this question, the expression on Xu Yun's face couldn't help but become a little more dignified, and he only heard him say:

"It is rumored that a long time ago, there was a sage named Shi Hao from the Fenglingyue Shadow Sect, who was extremely intelligent since he was a child.

He discovered that in all things in the world, every object with mass exerts a force on other objects with mass.

He named this force gravitation, and gravity is a component of gravity on Earth.

The gravity is vertically downward, so that all objects will fall freely after breaking away from the support. "

That's all.

Xu Yun couldn't help but look at Lao Su, afraid that the boss would ask again, "What is the essence of gravity".

After all, the essence of universal gravitation is a concept that later generations have never had a concrete conclusion on.

well known.

Although Maverick discovered gravitation, what he discovered was actually the mathematical definition of gravitation, not the physical concept of gravitation.

The solution to the concept of physics will have to wait until Einstein put forward the theory of relativity before the world will have a further understanding of gravitation:

The essence of gravitation is the curvature of space—or not just space, but four-dimensional space-time.

For relativity.

Space-time is a whole, described in terms of physics, flat space-time is called "Minkowski space".

And bending means that the metric of the flat Minkowski space has changed.

at the same time.

According to general relativity, it is the mass of matter that makes space-time bend.

Objects run along the shortest route in four-dimensional space-time (geodesic motion), and the form of motion is gravitational force.

Let’s take Xu Yun back then as an example.

Xu Yun fell to the ground.

calf says:

Oh, this is because the gravitational force of the earth pulled Xu Yun to the ground.

Einstein said:

No, it is the mass of the earth that bends the four-dimensional space-time around the earth, which is why Xu Yun fell down.

Xu Yun (called a test particle in physics terms) 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 to a certain point on the ground at a certain moment.

That is, Xu Yun is moving according to the four-dimensional geodesic line.

The projection of this four-dimensional geodesic movement in three-dimensional space is the trajectory of Xu Yun's falling from the tree.

Therefore, in later generations, the explanations of universal gravitation in the three mechanics are completely different.

In Maverick's classical mechanics, it is considered that gravity is a fundamental force produced by mass.

Einstein's general theory of relativity holds that gravity is caused by the curvature of space-time.

According to quantum mechanics, gravity is produced by the exchange of gravitons between matter.

It is impossible to know which of the above views is right or wrong, and it is still being debated today——"Science" is celebrating its 125th anniversary in 2018. also classified the question as one of the 125 most challenging science problems.

That's right.

Like bicycles, it is such a problem that junior high school physics will mention, and today's scientific community still has no specific conclusions.

Among the above three points, the qualitative scope of classical mechanics to gravity is relatively limited, and classical mechanics is not even used in many cases.

Therefore, some people always murmur that the general theory of relativity negates classical mechanics, which is actually a rascal statement.

Even in a novel written by Xu Yun in his previous life, the protagonist traveled to see Mavericks, and some people commented, "Why are you looking for Newton, classical mechanics is just nonsense".

Actually.

The way to judge whether classical mechanics is correct or not is actually very simple - just look at whether it has practical value.

It allows you to build airplanes, drive tanks, build tall buildings tens of meters or even hundreds of meters, and dive deep into the water.

It can be used in various fields of our macroscopic world, so it is very successful.

At least in the macroscopic world we can see now, you can absolutely believe it.

Remember that pendulum experiment:

Change the single pendulum into a beheading knife and let it out.

Then put the neck at its original position by 0.01 cm, do you dare to do it?

Anyway, Xu Yun dared to do it, and he did it, but he used an iron ball with the size of 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, it is a matter of ten to the eighty or nine powers at every turn, so classical mechanics is not very easy to use.

all in all.

The three have their own fields of adaptation, and classical physics is still strong and necessary in life.

Considering that during the Northern Song Dynasty, it might be possible to understand the microcosm, but what about the theory of relativity and quantum mechanics?

Unless old Su can recite poems until he is one hundred and thirty years old, it is impossible at all.

Therefore, Xu Yun's idea is to discuss gravity in the category of classical mechanics, and to impart knowledge according to the basic framework of classical mechanics.

The line of sight returns to reality.

Perhaps it is because there is no intuitive concept of gravity.

After listening to Xu Yun's explanation, Old Su didn't go further into the origin of this 'force'.

Instead, there was a whole new wave of doubts.

I saw him open his palm, put it beside Xiao Zhao and waved it, then looked at Xu Yun:

"Xiao Wang, according to what you said, there is a gravitational force between objects.

Then I was so close to Xiao Zhao and Xiao Li, why didn't I notice any attraction? "

Xu Yun looked up at Xiao Li and Xiao Zhao who were a little confused, and explained with a smile:

"Master, according to what Shi Hao said, gravity is the weakest type of force in the world.

The force is hardly noticeable, even less than a summer mosquito bite, so it's normal that you don't feel it. "

Hearing Xu Yun's explanation, Old Su hadn't responded yet, and Xiao Zhao, who had been silent all this time, couldn't help but speak:

"My lord, since this so-called 'gravity' is too small to be noticed, how do you know it actually exists?"

Xu Yun immediately cast an approving look at the fan, and then he pointed to a simple prop beside him and said:

"Of course it depends on this."

This set of props is about 40 to 50 centimeters high, and it is also made with tools found by Mr. Xie.

When Old Su was experimenting with chalk earlier, Xu Yun was tinkering with this thing.

And it can be assembled in a short time, so the material of this prop is naturally not too complicated:

The main body of the prop is a torsion scale that is not the same as the later generations, but has similar functions—yes, a torsion scale:

The prototype of the modern torsion balance was produced by Father Michel of the Royal Society in the 16th century, optimized in the 18th century, and finally finalized as the modern torsion balance.

But before that, there were some relatively primitive torsion balances in various ancient civilizations.

For example, the torsion balance invented by Lao Su in the Song Dynasty.

When Lao Su was supervising the production of the water transport instrument, in order to calculate the torque, he designed a classical torsion balance that could be finely calibrated.

The tool diagram was also drawn by Lao Su in "Shao Shengyi Xiang Fa Yao".

And at this very moment.

The torsion balance is tied to the bracket through a steel wire with good toughness, and two iron balls, one large and one small, are placed at both ends of the torsion balance.

There is a small mirror with low precision on the steel wire, but it can reflect normally.

That's right.

See here.

The students who were not pissed off by the physics teacher must have already guessed it.

The experiment that Xu Yun is going to conduct this time is the famous experiment of later generations.

Cavendish torsion balance experiment.