本帖最后由 choi 于 3-18-2024 11:52 编辑
In my posting titled 殲-35 and dated March 16, I expanded Note (a)(ii) by adding material after "Marshall Brain" -- starting with • Why does an acceleration unit include "per second per second"? to the end of (ii)(B), as shown below.
(ii) "推力14噸"
(A) 推力 thrust
https://en.wikipedia.org/wiki/Thrust
("Force, and thus thrust, is measured using the International System of Units (SI) in newtons (symbol: N), and represents the amount needed to accelerate 1 kilogram of mass at the rate of 1 meter per second per second")
(B) Marshall Brain, How Gas Turbine Engines Work. howstuffworks, undated
https://science.howstuffworks.co ... modern/turbine7.htm
("Thrust is generally measured in pounds in the United States (the metric system uses Newtons, where 4.45 Newtons equals 1 pound of thrust). A "pound of thrust" is equal to a force able to accelerate 1 pound of material 32 feet per second per second (32 feet per second per second happens to be equivalent to the acceleration provided by gravity). Therefore, if you have a jet engine capable of producing 1 pound of thrust, it could hold 1 pound of material suspended in the air if the jet were pointed straight down. Likewise, a jet engine producing 5,000 pounds of thrust could hold 5,000 pounds of material suspended in the air. And if a rocket engine produced 5,000 pounds of thrust applied to a 5,000-pound object floating in space, the 5,000-pound object would accelerate at a rate of 32 feet per second per second")
• Why does an acceleration unit include "per second per second"?
Newton's laws of motion
https://en.wikipedia.org/wiki/Newton%27s_laws_of_motion
(section 1 Prerequisites: v=ds/dt + a=dv/dt (which explains why the unit of acceleration includes "per second second"/ section 2 Laws, section 2.2 Second law: F=ma)
newton (unit)
https://en.wikipedia.org/wiki/Newton_(unit)
(1 kg⋅m/second squared )
• Why 32?
Intuitively, one guesses that the number is needed to have a pound of object suspended in the air.
pound (force)
https://en.wikipedia.org/wiki/Pound_(force)
(symbol: lbf, where lb is pound and f force)
is pound thrust. See section 4 Pound of thrust.
Also in this Wiki page, section 1 Definitions, section 1.1 Product of avoirdupois pound and standard gravity: a formula explains the origin of "32")
The "avoirdupois pound" is the pound that is used in the US (and before, in England, which mainly uses metric system) and equals 0.45 kg.
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(1) Miriam Jordan, Afghanistan in Their Rearview, Mr Gil in Their Passenger Seat. New York Times, Mar 17, 2024, at page A1.
https://www.nytimes.com/2024/03/ ... -women-driving.html
Note:
(a) "Afghanistan in Their Rearview" mirror means leaving Afghanistan.
(b)
(i) Gil Howard's full first name is Gilbert.
(ii) Modesto, California
https://en.wikipedia.org/wiki/Modesto,_California
(table: population (2020) 218,464; "Modesto is located in the Central Valley, 68 miles (109 km) south of Sacramento and 90 miles (140 km) north of Fresno"/ section 1 History: name)
(c) "Mr Howard, who lives alone and has grown children, moved to Modesto in 2012, after decades teaching operations research and mathematics at the Naval Postgraduate School in Monterey, Calif."
(i) operations research
https://en.wikipedia.org/wiki/Operations_research
(ii) operations research. Encyclopaedia Britannica, undated
https://www.britannica.com/topic/operations-research
("operations research is not a science itself but rather the application of science to the solution of managerial and administrative problems")
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Bibifatima Akhundzada wove a white Chevy Spark through downtown Modesto, Calif., on a recent morning, practicing turns, braking and navigating intersections.
“Go, go, go,” said her driving instructor, as she slowed down through an open intersection. “Don’t stop. Don’t stop.”
Her teacher was Gil Howard, an 82-year-old retired professor who happened upon a second career as a driving instructor. And no ordinary instructor. In Modesto, he is the go-to teacher for women from Afghanistan, where driving is off limits for virtually all of them.
In recent years, Mr. Howard has taught some 400 women in the 5,000-strong Afghan community in this part of California’s Central Valley. According to local lore, thanks to “Mr. Gil,” as he is known in Modesto, more Afghan women likely drive in and around the city of about 220,000 than in all Afghanistan.
For many Americans, learning to drive is a rite of passage, a skill associated with freedom. For Afghan immigrants it can be a lifeline, especially in cities where distances are vast and public transportation limited. So when Mr. Howard realized the difference driving made to the Afghan women, teaching them became a calling, the instruction provided free of charge.
He has a wait list 50 deep and a cellphone inundated with texts from people seeking slots. Through word of mouth, he recently got an inquiry from Missouri.
After the Taliban returned to power in Afghanistan in 2021 and instituted a strict Islamic rule, they banned girls and women from schools and universities and barred them from driving.
But even before the fall of Kabul, most Afghan women rarely got behind the wheel. In Afghanistan’s conservative society, women are often kept at home unless accompanied by male family members.
In the United States, Afghan newcomers tend to preserve religious and cultural customs: Most women wear head scarves, or hijabs. Many who are learning English prefer single-sex classes. Married women who were interviewed for this article agreed to be photographed only if their husband consented, and many let men speak on their behalf.
Yet when it comes to driving, many Afghan women are keen to assimilate — though you will not hear them invoke gender equality or empowerment. Their principal motivation? Getting from point A to point B.
“It was my goal to drive to help the family,” said Latifa Rahmatzada, 36, who got her license last September.
In Kabul, Ms. Rahmatzada, the mother of three young boys, had been mainly confined to the extended family’s compound. Shopping was a man’s job. On rare outings, she was escorted by her husband or a male relative.
Nearly 7,500 miles away in Modesto, she had no trouble convincing her husband, Hassibullah, to give her the greenlight to drive. “I supported her right away. It was so stressful for me doing everything,” he said, and so he contacted Mr. Howard.
These days, while her husband is working nine-hour shifts stocking shelves at Walmart, Ms. Rahmatzada is often steering a 1992 Honda Accord — it had logged some 190,000 before it was donated to them — to their sons’ elementary school, the supermarket and other places around town.
The United States is home to about 200,000 Afghans, concentrated in California, Texas and Virginia. Roughly half of them have arrived since the U.S. military withdrawal from Afghanistan in 2021, and more are on their way.
Coming from a country where traffic lanes, lights and signs were virtually nonexistent, even men who drove in their homeland face a big adjustment to the rules of the road in the United States. Some do not feel qualified to teach their spouses.
“All Afghan women and men are happy with Mr. Gil’s classes,” said Ms. Akhundzada’s husband, Sangar.
It became essential for Ms. Akhundzada, 22, to learn to drive after her husband started driving for Uber several days a week in San Francisco, 90 miles away.
“She needs driving to bring groceries, bread and for going to the park with kids,” Mr. Akhundzada said.
Ms. Akhundzada speaks little English, but in California, driving tests are offered in 38 languages. She was able to pass the exam for her learner’s permit in Dari, the most widely spoken language in Afghanistan.
She then waited several months until Mr. Howard could squeeze her into his schedule.
Mr. Howard, who is quietly firm with his students, uses simple English and hand gestures for instruction. But he has also learned key words in Dari, like left, right, stop and go, to communicate with his pupils, and he used them while crisscrossing Modesto with Ms. Akhundzada.
“You’re learning pretty fast,” he said, after she parallel parked. “Another lesson or two and you’re ready to go.” Ms. Akhundzada responded with a giggle.
Mr. Howard, who lives alone and has grown children, moved to Modesto in 2012, after decades teaching operations research and mathematics at the Naval Postgraduate School in Monterey, Calif.
“I thought I would work on my garden and do some traveling,” he said.
Moved by images of migrants drowning during attempts to cross the Mediterranean and reach the West, Mr. Howard decided to volunteer at World Relief, a nonprofit that helps to settle refugees in the United States. Soon he was furnishing apartments for refugees, ferrying them to appointments and distributing secondhand bicycles.
Many of the refugees had fled Afghanistan after their lives were threatened for working alongside U.S. troops. Mr. Howard took a deep interest in some of the families.
Unexpectedly, his 65 years of driving experience came in handy.
In 2017, two Afghan sisters who had settled in the area with their mother and young brother asked if he would teach them how to drive.
Mr. Howard initiated them in an empty parking lot.
“I had never seen a woman driving a car in Afghanistan,” recalled Morsal Amini, 24, one of the sisters. “Here it is so hard if you can’t drive.”
“D is for drive, R is for reverse, P is for parking,” Ms. Amini recalled Mr. Howard telling her.
Once the sisters had mastered the basics, they began plying country roads and then city streets with their instructor, whom Ms. Amini described as an “angel, comforting and patient.”
There was a close call when a truck stopped in front of her — and Ms. Amini did not immediately react. “Didn’t you see the brake lights?” Ms. Amini, now 24, recalled Mr. Howard asking her. She had no idea what they were.
It took a few tries, but both women passed their road tests and bought a car. “Our life changed completely,” Ms. Amini recalled.
So did Mr. Howard’s.
Soon he was fielding a steady stream of requests to teach other Afghan women. Many of them had taken an “English for Driving” course at Modesto Junior College. Initially, some were accompanied to lessons by chaperones, like an older brother or male relative, who sat in the back seat.
When women were ready for the road test, Mr. Howard would usually accompany them.
Demand for his tutelage soared after the Taliban seized control of Afghanistan in 2021, ushering in a fresh wave of Afghan evacuees to the United States, including Modesto.
To keep track of his expanding roster of students, he created a spreadsheet on his cellphone and prioritized those with learners’ permits close to expiring.
Some days, he teaches five back-to-back classes, each 90 minutes to two hours long.
His only qualm, he said, was that his blood pressure has risen from all the oil and salt in the rich Afghan food that he receives from students as a token of their appreciation.
On a recent Wednesday, Mr. Howard’s second pupil of the day was Zahra Ghausi, 18, whose road test was scheduled for the following week.
The college student was cruising down a residential street when she approached a school. “Watch the speed,” said Mr. Howard, his hand resting atop the hand brake, just in case.
He instructed her to get on the 99 Freeway. At 65 miles per hour, Ms. Ghausi sped by almond groves that lined the highway and changed lanes to pass a truck laden with metal sheets. The speedometer read 70 m.p.h.
“This is one I don’t have to say ‘go, go, go’ to,” Mr. Howard said. “She goes.”
Ms. Ghausi exited at Taylor Road and zipped to California State University in nearby Turlock.
“I just love driving,” she said, pulling into the campus. “I really love sports cars, too. Hopefully, one day I’ll drive a racing car.”
Mr. Howard then headed back to Modesto. There was another student waiting for a lesson.
A correction was made on March 16, 2024: A photo caption in an earlier version of this article misspelled the given name of one of the driving students. She is Zahra Ghausi, not Zahira.
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