Subsequently, there is gravitational force between objects, so just place two iron balls C and D of the same mass near the two iron balls A and B on the torsion balance.

Then gravitational force F1 will be generated between A and C, and gravitational force F2 will be generated between B and D.

The magnitudes of the two gravitational forces are different, somewhat resembling a tug of war in later generations.

So at this time, the torsion balance will slightly deflect, and the reflected far point will also move a greater distance.

According to Cavendish's experiment records.

He calculated the density of the Earth to be 5.481 times that of water, which is 5.481 grams per cubic centimeter.

Compared with the data of the 21st century, this is only a 0.65% error.

As for the gravitational constant G, Cavendish actually did not calculate it, after all, the cognitive system at that time was still not fully developed.

But in his experimental records, the data for calculating G is already quite complete, yet it is just a conceptual understanding.

Even today's high school students can easily calculate the gravitational constant, and quite accurately.

So people later decided to award the title of measuring the gravitational constant G to Cavendish in honor of this great experimental physicist.

In fact, given Cavendish's learning, if he chose to publish his results, his fame would certainly be much greater than it is now.

If we have to look for a reason.

It's probably because God spent too much ink depicting his wisdom, that He could not draw a better personality for him.

For example, although he was exceedingly wealthy, he wore nothing but a faded velvet coat and an outdated tricorn hat for years.

His character was reclusive and reticent; he hardly dared to converse with strangers and the opposite sex.

Even when communicating with his hired steward, he only used note-passing methods to avoid awkwardness.

He was the largest depositor in London Bank, but he was completely indifferent to his wealth.

For decades, he instructed his investment advisor to only buy one kind of stock, unchanged until his death.

When a servant's parents had a fever, he directly gave a medical fee equivalent to three hundred thousand in later generations.

Moreover, he complained more than once in letters to friends about having too much money and not knowing how to spend it.

In fact, big figures like Cavendish are not uncommon in history, for instance, Gauss was a very typical example.

After Gauss died, he left a bunch of unpublished manuscripts, and whoever could interpret them in the next 50 years was considered a big shot.

The sight returns to the original place.

The core of Cavendish's torsion balance experiment, simply put, is two words:

Amplification.

Cavendish used three amplifications in his experiment:

Firstly, converting force into torque, amplifying the force.

Secondly, using the law in geometric optics, that when a plane mirror rotates θ, the reflected light rotates twice θ, amplifying the angle.

Thirdly, converting angular displacement into linear displacement, using a ruler to measure the displacement of the reflected light spot, calculating the rotation angle, amplifying the macroscopic displacement.

These three amplifications are the innovative points of this experiment.

Certainly.

Considering the tools Xu Yun can currently find, conducting a torsion balance experiment in the Northern Song might have significant errors.

But do not forget.

The goals of him and Cavendish also differed:

Cavendish conducted the torsion balance experiment firstly to verify universal gravitation, and secondly to calculate the Earth's density and mass through data, and the information collected also deduced the gravitational constant.

Whereas Xu Yun right now only needs to reproduce the phenomenon and prove that there is gravitational force between objects, without needing to calculate specific values.

As for the slender light beam needed for the experiment, it's not difficult:

Some marketing accounts in later generations introduced Cavendish's experiment saying he used lasers, and it didn't seem to be a problem.

But as long as you understand the history of technology, you will know:

The principle of lasers was invented by Einstein in 1916.

Therefore, Cavendish's real operation was to first move the equipment into a dim room and fix the position.

Then, using the inverse relation between the divergence angle and the radius of the light spot, w0X2θ0=w0'X2θ0'=2λ/π as the design basis, simply making a glass lens would do.

A quarter of an hour later.

The entire set of equipment was debugged to completion.

Xu Yun asked Mr. Xie to stand outside the room, with a tool similar to a selfie stick stuck into the ground beside him.

The lens was fixed to the top of the tool, which could be rotated simply.

A few minutes later, Xu Yun said:

"Old Chief Steward, you can start now."

Mr. Xie nodded and had no objections to Xu Yun's instructions:

"Understood."

Then he slowly rotated the lens according to Xu Yun's previous instructions, beginning to calibrate the light.

Xu Yun's gaze remained fixed on the mirror, closely watching the changes in the light.

After a while, he suddenly said:

"Stop! Right at this position!"

Mr. Xie hurriedly stopped the rotation.

Then Xu Yun turned around and said to Xiaozhao:

"Prince Jian, could you please mark the position of the light spot on the wall with chalk?"

Xiaozhao obediently took a piece of chalk and walked to the wall.

He drew a thumb-sized white dot at the position of the reflected light spot:

"Mr. Wang, is this okay?"

Xu Yun nodded at him and then said to Old Su:

"Elder, it's our turn."

Old Su, upon hearing this, rolled up his sleeves and picked up an iron ball from the table, approaching the small iron ball on the left side of the torsion balance.

Xu Yun picked up another iron ball and approached the large iron ball on the right.

As the iron balls approached, some imperceptible changes occurred.

In less than a moment.

Xiaozhao at the wall suddenly narrowed his eyes and exclaimed in surprise:

"Junior Master, the light spot... moved!"

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