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2019-12-19, 12:22 PM (ISO 8601)
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Re: OOTS #1189 - The Discussion Thread
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2019-12-19, 12:24 PM (ISO 8601)
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- Dec 2018
Re: OOTS #1189 - The Discussion Thread
That sounds really confusing. Thanks
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2019-12-19, 12:28 PM (ISO 8601)
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- Aug 2009
Re: OOTS #1189 - The Discussion Thread
"Rocket surgery" works. (I'm a bit biased on such terminology, as my wife is a brain scientist.)
I'm not weirded out by odd units. They happen, from time to time; eventually, they cancel out, possibly with a few conversions along the way. Even that hypothetical distance in units of miles2/ft isn't intrinsically wrong, since the dimensions are correct; it's just that the number is about seven orders of magnitude smaller than one might expect if the intended result was in ft. Multiply it by (5280 ft/mile) twice and you're fine. The problem comes if you have a number (without units) which is supposed to represent a distance in miles, divide it by 5280, and write in "feet". Doing the calculations with just the numbers, and dropping in the units you expect at the very end, is begging for trouble.
One of the most challenging parts of teaching people to do calculations in the physical sciences is to get them to look at the final result critically: does it make sense, or is it a silly number? "Your final result is a pressure of negative a hundred thousand atmospheres. What is that even supposed to mean?" "But that's what the calculator says!"Last edited by bunsen_h; 2019-12-19 at 12:32 PM.
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2019-12-19, 12:40 PM (ISO 8601)
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- Dec 2019
Re: OOTS #1189 - The Discussion Thread
Dr. Doug, have you read "Ignition!" by John D Clark? If yes what's your opinion of it?
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2019-12-19, 01:15 PM (ISO 8601)
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- Oct 2006
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- Meridianville AL
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Re: OOTS #1189 - The Discussion Thread
My little sister tells of a student coming to her office to ask for help back when she was a GTA. He had a homework problem asking what the displacement from a vertical drop due to Coriolis effect would be in a 20m fall at their latitude.
IIRC, the correct answer was ~1cm to the east. His result was 10km to the west. She pointed out the window of her office at the UC Berkeley clock tower, "You see that clock tower?"
"Yes"
"You see the golden gate bridge"
"Yes"
"Are you telling me that if you drop a rock off the top of that clock tower it will hit that bridge on the way down?"
"I guess so."
Apparently, the student still failed to make the obvious connection that he'd made a small mistake somewhere.
I once goofed writing a question, and out of an entire class, only one student asked if the vehicle (on wheels) was actually supposed to be traveling at over 300 miles per hour. IIRC I told her prior to the final that she didn't need to show up if she didn't want to, as she clearly had an A for the class.
Haven't read it. But first hand accounts are often interesting when you're looking into something.
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2019-12-19, 01:47 PM (ISO 8601)
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- May 2018
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Re: OOTS #1189 - The Discussion Thread
How about ‘it’s not a GitP thread?’ That’s the most complicated thing I can think of right now.
Like Star Wars, ponies, and/or unabashed silliness? Check out my YouTube channel, Nothing In Particular, for a healthy dose of absurdity. It's just what the doctor ordered!*
* Surgeon General's Warning: May cause chronic hideous laughter, eye rolling, or beleaguered sighs. Not intended to prevent, diagnose, or treat any disease.
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2019-12-19, 02:03 PM (ISO 8601)
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- Dec 2009
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- Birmingham, AL
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Re: OOTS #1189 - The Discussion Thread
Imean, if they got 10km displacement on a 20m drop to begin with and didn't object...
Also, Ignition! is literally in a pile of books I need to read at home right now! It took a backseat to Moon Lander: How We Developed the Apollo Lunar Module, though. The LM's my favorite spaceship by far, that one was always going to be read first. Grumman built one hell of a machine.
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2019-12-19, 02:21 PM (ISO 8601)
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- Dec 2019
Re: OOTS #1189 - The Discussion Thread
N years ago a quote from it about chlorine trifluoride was making rounds on the interwebs:
It is, of course, extremely toxic, but that's the least of the problem. It is hypergolic with every known fuel, and so rapidly hypergolic that no ignition delay has ever been measured. It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water—with which it reacts explosively. It can be kept in some of the ordinary structural metals—steel, copper, aluminum, etc.—because of the formation of a thin film of insoluble metal fluoride that protects the bulk of the metal, just as the invisible coat of oxide on aluminum keeps it from burning up in the atmosphere. If, however, this coat is melted or scrubbed off, and has no chance to reform, the operator is confronted with the problem of coping with a metal-fluorine fire. For dealing with this situation, I have always recommended a good pair of running shoes.
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2019-12-19, 02:22 PM (ISO 8601)
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- Feb 2010
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- France
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Re: OOTS #1189 - The Discussion Thread
As someone with 5 years of experience as a ground technician in the European Space Center of French Guyana. I can relate to what Doug is saying.
We obviously have less problems with units, but still have some.
There were the various unit used for pressure (Why the use mmHg ?), but what really annoyed me was the millimetres and inches being mixed for the diameters of pipes and bolts, including on blueprint. I also have a problem with VoltAmpère being different from Watt.
And i also can relate a lot to his depiction of the behaviour of rocket scientists or engineers. There are some engineers who won't say "Bonjour" to you if you're not an engineer yourself.
Oh yes... this one has always annoyed me.
I can relate to the first one, we often use distance-per-full-tank here.
Car sellers often advertise on volume per 100 km, though.
What's exactly a "machinist"?
I once wrote a test for my associates degree students about power transmission. It was about the Audi A8 W12 530HP (yes, you can guess what movie i saw a few days before).
I asked to calculate the maximum speed of the car given the motor gear chart and size of the wheels.
I got 200 000 km/h and 60 km/h among the answers.Last edited by Petrocorus; 2019-12-19 at 02:31 PM.
Que tous les anciens dieux et les nouveaux protègent la France.
Resistance Data in MM, Volo's, MToF. -- -- Petrocorus's 3.5 Paladin Builds List. -- -- French vs. EnglishOriginally Posted by King Louis XIII in The Musketeers
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2019-12-19, 02:42 PM (ISO 8601)
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- Feb 2007
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- Manchester, UK
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Re: OOTS #1189 - The Discussion Thread
There's a good reason for that one, though. If your AC voltage and current are exactly in phase then VA and W are identical, but if they're OUT of phase (e.g. you have a power factor less than 1) then they're different values--VA is literally just the RMS voltage multiplied by the RMS current, whereas Watts is the actual real power dissipated in the system. Source: trained as an electrical engineer many years ago.
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2019-12-19, 03:14 PM (ISO 8601)
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- Feb 2013
Re: OOTS #1189 - The Discussion Thread
What's exactly a "machinist"?
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2019-12-19, 03:15 PM (ISO 8601)
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- Feb 2010
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- France
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Re: OOTS #1189 - The Discussion Thread
I understand (i think) the difference between real and apparent powers, but for me, the apparent power is still a power and i feel like it should be said in Watt.
Of course, my bachelor is in mechanical engineering, so i may be completely misunderstanding this. Maybe it's akin to the centrifugal force not being a force at all.Que tous les anciens dieux et les nouveaux protègent la France.
Resistance Data in MM, Volo's, MToF. -- -- Petrocorus's 3.5 Paladin Builds List. -- -- French vs. EnglishOriginally Posted by King Louis XIII in The Musketeers
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2019-12-19, 03:47 PM (ISO 8601)
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- May 2018
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2019-12-19, 04:10 PM (ISO 8601)
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- Oct 2006
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- Meridianville AL
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Re: OOTS #1189 - The Discussion Thread
Guy who uses things like Lathes and drill-presses to make other machinery mostly. AKA, the guy who actually makes the parts that go into the rocket.
Mandatory XKCD link:
https://xkcd.com/123/
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2019-12-19, 04:27 PM (ISO 8601)
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- Oct 2006
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- Meridianville AL
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Re: OOTS #1189 - The Discussion Thread
That's actually a quote from Ignition! Mentioned earlier in the thread.
The source for most of the web references is a quote in:
https://blogs.sciencemag.org/pipelin..._you_this_time
See for the index of a bunch of such articles.
https://blogs.sciencemag.org/pipelin...wont-work-with
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2019-12-19, 04:39 PM (ISO 8601)
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- Dec 2019
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2019-12-19, 09:14 PM (ISO 8601)
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- Feb 2007
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- Manchester, UK
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Re: OOTS #1189 - The Discussion Thread
The distinction can be important. For instance, uninterruptible power supplies often have both a VA rating and a watt rating, and you don't want to be exceeding either limit for safety reasons. This is why the SI system of units allows for both watts and VA to be separate units, even though they're dimensionally the same.
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2019-12-19, 09:42 PM (ISO 8601)
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- Dec 2013
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Re: OOTS #1189 - The Discussion Thread
By far, my least favorite unit I've come across is how cross section is sometimes defined. It comes out as m2*, but you get that from (particles/second)/(particles/second/area)).
*or, if you prefer barns, one of which is 10-28 meters2
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2019-12-20, 12:41 AM (ISO 8601)
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- Dec 2018
Re: OOTS #1189 - The Discussion Thread
Why would cross section require particles
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2019-12-20, 01:04 AM (ISO 8601)
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- Dec 2019
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Re: OOTS #1189 - The Discussion Thread
When I was a TA during my phd in civil engineering, we used to ask questions like "if 6 people of 90 kg stand on this balcony, what would be the tip displacement" or "if a wind of this much is blowing over this building, how much will it deflect". The solutions were extremely simplified (it was statics - a second years course) and we sometimes got results in the range of few hundred meters to kilometers. It was always fun to read answer of someone who does not have a sense of magnitude.
When I was a student, we were having field measurement and surveying course, and asked to measure the elevation difference between top and bottom of seats of university stadium. We asked a fellow group member to record the measurements with pen and paper, and asked her to calculate the result in the end. The correct answer was around 10 meters and when she said 132 meters, there was an awkward silence. So it is not as fun when you are involved in the case
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2019-12-20, 04:30 AM (ISO 8601)
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- Aug 2013
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2019-12-20, 09:15 AM (ISO 8601)
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- Aug 2007
Re: OOTS #1189 - The Discussion Thread
Because you are trying to measure the area where a particle you've just blown up, or accelerated to a close to c, might have crossed. Thus why they use barn, a absolutely tiny area (as in "you couldn't hit the side of that barn", as applied to trying to hit a uranium nucleus with a helium nucleus).
Grey WolfLast edited by Grey_Wolf_c; 2019-12-20 at 09:17 AM.
Interested in MitD? Join us in MitD's thread.There is a world of imagination
Deep in the corners of your mind
Where reality is an intruder
And myth and legend thrive
Ceterum autem censeo Hilgya malefica est
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2019-12-20, 12:12 PM (ISO 8601)
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- Sep 2019
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- Florida
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Re: OOTS #1189 - The Discussion Thread
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2019-12-21, 02:17 PM (ISO 8601)
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- Feb 2017
Re: OOTS #1189 - The Discussion Thread
Can we go back to the translation topic? I was quite enjoying that...
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2019-12-21, 07:36 PM (ISO 8601)
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- Jul 2016
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- Seoul
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Re: OOTS #1189 - The Discussion Thread
Cool elan Illithid Slayer by linkele.
Editor/co-writer of Magicae Est Potestas, a crossover between Artemis Fowl and Undertale. Ao3 FanFiction.net DeviantArt
We also have a TvTropes page!
Currently playing: Red Hand of Doom(campaign journal)Campaign still going on, but journal discontinued until further notice.
Extended sig here.
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2019-12-21, 07:41 PM (ISO 8601)
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- Jul 2019
Re: OOTS #1189 - The Discussion Thread
Arrrgh, here be me extended sig!
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2019-12-21, 07:50 PM (ISO 8601)
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- Jul 2016
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- Seoul
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Re: OOTS #1189 - The Discussion Thread
Cool elan Illithid Slayer by linkele.
Editor/co-writer of Magicae Est Potestas, a crossover between Artemis Fowl and Undertale. Ao3 FanFiction.net DeviantArt
We also have a TvTropes page!
Currently playing: Red Hand of Doom(campaign journal)Campaign still going on, but journal discontinued until further notice.
Extended sig here.
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2019-12-21, 07:53 PM (ISO 8601)
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- Dec 2009
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- Birmingham, AL
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Re: OOTS #1189 - The Discussion Thread
Both "the need of the many" and "there's only one right path" sound fitting for her afterlife, solely based on the foundation idea.
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2019-12-21, 08:05 PM (ISO 8601)
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- Jul 2016
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- Seoul
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Re: OOTS #1189 - The Discussion Thread
Cool elan Illithid Slayer by linkele.
Editor/co-writer of Magicae Est Potestas, a crossover between Artemis Fowl and Undertale. Ao3 FanFiction.net DeviantArt
We also have a TvTropes page!
Currently playing: Red Hand of Doom(campaign journal)Campaign still going on, but journal discontinued until further notice.
Extended sig here.
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2019-12-21, 08:40 PM (ISO 8601)
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- Dec 2009
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- Birmingham, AL
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Re: OOTS #1189 - The Discussion Thread