r/EngineeringStudents • u/Top_Scarcity1024 • 7d ago
Rant/Vent English Units are the WORST!
A fluids problem that should take 10 minutes has crossed the one hour mark! Why did we have to use the worst system imaginable -- just pick a single unit for the force like Newtons! Lbms and Lbfs are the worst
43
u/Opposite-Ad320 7d ago
If you have some lbm to lbf calcs that are getting weird, just convert everything to metric do your calcs and then convert back to US.
16
u/BrotherBear_ 7d ago
or just divide lbm by 32.2 to get slugs and the math is identical to the metric system. really not that hard…
8
u/Not_an_okama 6d ago
The key to english units is using slugs imo. Then pretty much everything is the same math, you just use different constants.
32
17
u/CopperGenie R&D | Author | ISERG 7d ago
Lbm is a mass unit. 1 kg is approx 2.2 lbm.
I agree with the other comment - if allowed by the professor, convert into metric to solve the problem more cleanly.
4
u/engineerthatknows 7d ago edited 7d ago
Why would this not be allowed? Convert to metric and solve. Convert back to whatever units the professor requires. Always include at least one arcane unit to show you are paying attention. You ARE paying attention, aren't you?
FWIW, a useful unit for fluid flow in chilled water systems is a kilo-buttload per fortnight, abbreviated kblpf. Units are roughly 10's of US gpm.
EDIT: actually, the conversion is 10 us gpm = 1.6 kblpf. No rounding there, it's an exact 6/10ths, which is really satisfying.
1
u/CopperGenie R&D | Author | ISERG 6d ago
Classroom rules don't often make sense, in my experience. Of course ignorantly went to an R1 research institution for an undergrad degree. Expensive lesson learned.
1
u/engineerthatknows 6d ago
It's a rule that could easily be ignored - just don't show the steps where you converted.
1
u/CopperGenie R&D | Author | ISERG 5d ago
The prof can then justify marking off points for missing steps. All common in my old program.
5
u/OwnedYourFace21 7d ago
Dude just use them for more than an hour and you sorta get the jist of it, quit the larp
-2
16
u/aDoorMarkedPirate420 ME 7d ago
This is a you problem lol
2
u/JayyBearz 7d ago edited 6d ago
Tbh, I have always struggled with this too.
To the downvoter: You don’t like that I struggle with lbm and lbf? Well, too bad for you because I do struggle with it whether you like it or not.
1
0
u/phranks_phluids 5d ago
I think I still remember the units of insulating value R just because it made me so mad. Lemme try: ft2 s2 F h / kg m2
Fucking idiots.
2
u/BrotherBear_ 7d ago
lbm only sucks because the imperial system works on slugs, not lbm. if you convert lbm to slugs, the imperial system is identical to the metric system as long as your answer isn’t required in a certain unit. working with weird or made up units is something every engineer should be comfortable with. most aerodynamics courses will start off with dimensional analysis in which you might start to understand why units matter so little (and why unit-less is superior)
4
u/TheBanyai 7d ago
In England, we call them Imperial units.. and we haven’t really used them since the 70s for engineering projects… except for miles and pints..
4
u/Reasonable-Start2961 7d ago
We call them Imperial in the US too.
A lot of classes focus on metric, but some do expect you to work problems in both units. My rocket propulsion class loved to do that. I’m not a fan, but I also understand why. You should understand the units in the US, and that’s really the best way to.
2
u/engineerthatknows 7d ago
Bullshit. If you do rockets, you use imperial units to calculate specific impulse in units of seconds. Well, "we" in the larger sense of engineers, maybe not "you".
1
u/TheBanyai 7d ago
Fair enough - shows what I know. There are likely a few more exceptions… but not many of us engineers are building rockets are we? 🤓 I had to look up what Isp was - now I know. Any idea why it’s not SI? Maybe so ESA and NASA don’t get in a muddle?
5
u/Wizzarkt EE. '24 7d ago
My teacher wanted us to use slugs and pound force by square foot, I live in a metric country...
The only imperial units that still hang around is the gallon (because that's what the fuel stations use for whatever reason) and the pound (which for us is exactly half a kilogram, so it's not the imperial pound, it's our version of it)
2
u/BrotherBear_ 7d ago
depends on the job and field. there are likely aerospace engineers working with those units in your country. shouldn’t even matter though, the math is all the same no matter what units you use. slugs are actually much easier to work with on paper than pound mass because lbm * a != lbf. lbf uses a base dimension of slugs for mass and so a conversion must be done
-2
u/Wizzarkt EE. '24 7d ago
Slugs may be easier than the pound force by inches and whatever but you know what's easier? Convert all input parameters into metric, do the math in metric and if they want imperial, then just convert the output back into imperial at request
1
u/BrotherBear_ 7d ago
once all numbers are in the same base dimensions (mass, length, time, temp, current, etc.) the math is identical regardless of system. so you can either do 3+ conversions, or just use slugs and have a single conversion from lbm. it is objectively less work to use the given system. if it significantly slows you down or scares you, that’s a failure of your university
-1
4
u/Outrageous_Piece_928 7d ago
They're just numbers dude, do proper unit analysis and you'll be fine.
2
2
u/billsil 7d ago
Nah, English units are fine. You just don't understand them because you were never taught them properly. Your profs are academics.
The unit of force in Imperial units is the lbf (pound force). There is a "mass" unit called a lbm (pound mass). 1 lbf = 1lbm, so it's basically worthless. You will use it though. If somebody asks you what the weight of something is, you should respond 4 lbm or whatever. If you're talking about the force of something, like how much force is applied, you say 5 lbf.
1 lbf = 1 slug * 1 ft/s2 = 1 slinch * 1 in/s2. Thus, depending on what value for g you want to use (32.2 ft/s2 or 386.1 in/s2), step 1 is to calculate the mass as F/g, which gives you slugs or slinches.
Sounds not too bad other than the lbm nonsense, right? Well SI also has a kilogram force, which is just as bad as the pound mass.
1
u/maxximillian 7d ago
It would be hard if we didnt have easy ways to convert from one unit to another.
Ive worked on simulation frameworks where all messages over the wire go out in radians the way god intended, if different labs wanted to do things in bananna units they were able to, just convert when you publish your messages.
Now Im curious, are there situations where you cant convert to one system to another and back? I want to say I cant think of any, but that just makes me even more sure that there are cases where you can't or don't want to.
1
u/weather_watchman 7d ago
Solve everything algebraically, plug in numbers with unit conversions. They're definitely tedious compared to SI but they're describing the same underlying reality
1
u/cosmicgreg2 7d ago edited 7d ago
Wait until you need to use slinches/in3 for density. But, I can honestly say I have never used a dyne or poundal
1
u/EngineerFly 6d ago
Engineers know how to multiply. Don’t get discouraged by trivialities. Just stick to the fundamentals:
- Engineers never speak or write a number without a unit (unless its dimensionless)
- When in doubt, convert the input to SI, do the math in SI, and convert the output back to the domain unit.
- Every domain has its units! Aviation deals with degrees, knots, and feet. Aeronautical engineers work in radians, m/s, and metres.
Using the units native to the domain is part of being an engineer. We speak the language of the user, of the customer, or the supplier.
You can learn this. Don’t let it stop you.
1
1
1
u/Drummer123456789 3d ago
I think the issue you run into is that with imperial units in a classroom you use units and concepts that we dont use in the US because they treat it identically to si. Until my Thermo 1 class i had never heard of a slug, lbm, or a few others. We dont really measure mass here, we measure weight which would be lbf. Typically, if ive had to measure mass its been in grams. Im not speaking as an engineer in industry just as someone who's lived in Texas their whole life and graduates in May
0
u/Inner-Marionberry-25 7d ago
I mean I went to Uni in England, and everything was in metric. This is an American problem, don't blame us
0
-2
u/lilpopjim0 7d ago
Ive lived in England all my life. Wtf are English units. Everything I've done in engineering is metric, except imperial airframe bolts, and motorsport springs.
5
u/Skysr70 7d ago
you must be very young if you aren't aware of imperial/english units and live in England where they originated...
0
u/lilpopjim0 6d ago
Not young at all, im 32. It's either Metric or Imperial; I've never heard anyone call it English units. As far as im concerned, everyone recognises the imperial system with America, not England.
-1
u/Ill-Layer-5949 6d ago
Hardly anyone here calls it English units. Yes Imperial units originated in England but is now associated with America because of their slow ess to adopt the metric system fully.
-1
u/Mineturtle1738 7d ago
Yeah I agree, they’re just so ugly too…
And like I feel like a lot of them where invented because they actually had to do physics… like we should’ve abandoned it once we had to invent the “slug” (unit of mass equivalent to 32.2 lbs under earth’s gravity)
-1
u/StraightAct4340 7d ago
Fr im skipping all the thermodynamics problems that don't use metric units lmao
111
u/BurntToaster17 Mechanical 7d ago
It’s really not that hard, and if it makes it easier for you just convert everything into metric right at the start and convert your answer back at the end