OOTS #1189 - The Discussion Thread

[Peelee]

Distance over volume gives -surface. It checks out.

It’s the only way that makes sense.

Impulse_(SPecific)Yeah, dividing miles (length) by volume (gallons) produces units of inverse area (inches^-2).

I was flaunting my superior formatting.

I want to thank Mr Lampert for an interesting and entertaining read on "Rock Scientist". I will have to change my vocabulary to not repeat the phrase "well its not Rocket Science" going forward. At this point I am not sure what the replacement will be, maybe "Brain Surgery", but it is clear I have use something else.

My go to is "it's not rocket surgery."

[CriticalFailure]

That sounds really confusing. Thanks

[bunsen_h]

I want to thank Mr Lampert for an interesting and entertaining read on "Rock Scientist". I will have to change my vocabulary to not repeat the phrase "well its not Rocket Science" going forward. At this point I am not sure what the replacement will be, maybe "Brain Surgery", but it is clear I have use something else.

"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!"

[Saint-Just]

Dr. Doug, have you read "Ignition!" by John D Clark? If yes what's your opinion of it?

[Doug Lampert]

"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!"

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.

Dr. Doug, have you read "Ignition!" by John D Clark? If yes what's your opinion of it?

Haven't read it. But first hand accounts are often interesting when you're looking into something.

[MossyMeow]

How about ‘it’s not a GitP thread?’ That’s the most complicated thing I can think of right now.

[Peelee]

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.

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.

[Saint-Just]

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.

Such fun!

[Petrocorus]

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.

Part 2: Mass vs. Force

I have had rocket scientists quote me thrust in kg-force. That is not a unit. As pointed out above, rocket science is the field of human endeavor where this distinction is most likely to make a practical difference, most people can just assume 1g, but not rocket science. kg is not a unit of force. I assume kg-force is 9.8 N.

Oh yes... this one has always annoyed me.

In America we measure efficiency in distance per volume, because in America bigger is always better.

The alternative is to measure volume per distance, which is absurd because it means the less fuel you use, the smaller the number. And smaller is always worse! Its clearly a ridiculous measure.

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.

I would recommend, "It's not rocket machining" except that no one would get it, as I said, someone involved is a genius, and since it isn't whoever prepares those blueprints and the pieces do fit together and not explode...

What's exactly a "machinist"?

Imean, if they got 10km displacement on a 20m drop to begin with and didn't object...

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.

[factotum]

I also have a problem with VoltAmpère being different from Watt.

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.

[Rogar Demonblud]

What's exactly a "machinist"?

Someone who uses a machine to make things, in simplest terms.

[Petrocorus]

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.

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.

[Dion]

I was flaunting my superior formatting.

I saw that, but I really just wanted any reason to say Hogshead^⅔.

[Doug Lampert]

What's exactly a "machinist"?

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.

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.

Mandatory XKCD link:
https://xkcd.com/123/

[Doug Lampert]

N years ago a quote from it about chlorine trifluoride was making rounds on the interwebs:



Such fun!

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

[Saint-Just]

That's actually a quote from Ignition! Mentioned earlier in the thread.

Um, it was I who first mentioned Ignition! ITT, and that's why I said "a quote from it".

And yes, I totally would've mentioned ItPL if I had been allowed to post links.

[factotum]

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.

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.

[Jaxzan Proditor]

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

[CriticalFailure]

Why would cross section require particles

[msoulforged]

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.

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

[snowblizz]

It’s the only way that makes sense.

In America we measure efficiency in distance per volume, because in America bigger is always better.

The alternative is to measure volume per distance, which is absurd because it means the less fuel you use, the smaller the number. And smaller is always worse! Its clearly a ridiculous measure.

Or put another way in America you want to know how far you can go on a tank of gas. In Europe you want to know how cheaply you can drive to work.

That checks out actually.

[Grey_Wolf_c]

Why would cross section require particles

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 Wolf

[Quizatzhaderac]

There are some engineers who won't say "Bonjour" to you if you're not an engineer yourself.

There's a famous story in the US, that took place at a NASA site.

President of the United States of America, John Fitzgerald Francis Kennedy: Hi, I'm Jack Kennedy. What are you doing?
Janitor: Well, Mr. President, I'm helping put a man on the moon.

[Riftwolf]

Can we go back to the translation topic? I was quite enjoying that...

[danielxcutter]

Can we go back to the translation topic? I was quite enjoying that...

Topics on an OotS thread tend to be quite similar to a Loodle on a sugar high.

[Schroeswald]

Topics on an OotS thread tend to be quite similar to a Loodle on a sugar high.

Wheeeee! Lets talk about Miko now!

[danielxcutter]

Wheeeee! Lets talk about Miko now!

Incidentally, do you even know what a Loodle is?

[Peelee]

Wheeeee! Lets talk about Miko now!

Both "the need of the many" and "there's only one right path" sound fitting for her afterlife, solely based on the foundation idea.

[danielxcutter]

Both "the need of the many" and "there's only one right path" sound fitting for her afterlife, solely based on the foundation idea.

Arcadia is one of the Upper Planes, and Mechanus isn't bad I guess.

I really hope she does go to her proper afterlife instead of being turned into an undead monster or something. I really do.

[Peelee]

Arcadia is one of the Upper Planes

Indeed. That was always my guess until that strip came out, at which point a started to wonder.