Agree. Perhaps a better way to say this is that the only place I have ever seen “<>” is in a programming language (Excel also uses it).
The fact of the matter is that there is a unit of mass in the Imperial system
called the slug. I remember this from physics in high school.
From Wikipedia:
The slug is an English unit of mass. It is a mass that accelerates by 1 ft/s² when a force of one pound-force (lbf) is exerted on it. Therefore a slug has a mass of 32.17405 pound-mass or 14.5939 kg.[1]
Using pounds as mass is pure crap.
Because the U.S. engineering and construction industry (as well as much of the manufacturing industry) are a bunch of hidebound traditionalists.
Also, while engineers at least learn the SI system in their general science classes, many technicians and construction workers are not at all familiar with it. This goes back to the general abandonment of converting the U.S. to the metric system. (That is, with the noted exception of the hard sciences, such as chemistry and physics, which are universally taught and worked in using SI units.)
In addition, all of the tools and instruments (everything from calipers to survey equipment) are in USCS units. Not to mention standard details, drawings, and specifications.
Finally, as I noted above, we don’t use imperial units. We use a system that is derived from the imperial system, but differs in many ways.
P.S. Also, I said that I often convert units to SI for easier calculations. This is uncommon, I think. Perhaps because I used to teach chemistry and physics, I’m very familiar and comfortable with the SI system, and appreciate its advantages.
True enough, but the OP was not about the imperial system. U.S. engineers do not use the imperial system, and I have never seen the slug used by engineers in the U.S.
I agree that the unit of pound-mass (lbm) is completely screwed up–but I didn’t invent it, either, so I take no responsibility for it.
I do recall the day that the units of pound-mass, pound-force, and g[sub]c[/sub] were first introduced in one of my engineering design classes. I remember being absolutely floored by how stupid and confusing it all was. Voicing this to the instructor simply resulted in the instructor noting that this was the industry standard.
Finally, as an aside, I’ll note that from a conceptual point of view, while using the pound as a unit of mass is indeed stupid, it’s just as stupid for metric spring scales to be calibrated in units of mass (such as kilograms) instead of newtons. People all over the world routinely confuse force and mass units.
Truer words were never spoken.
I have. I was taught to use slugs in most physics and engineering classes, and use slugs preferentially myself. When I taught classes, I taught using both slugs and pounds-mass (as well as SI units). Most of the folks I work with know perfectly well what a slug is, although most also voice a preference for doing calculations in SI units, for reasons that are obvious.
Out of curiosity, when did you graduate? (I graduated from college in the early 1990s.)
While I certainly know what a slug is, I have never used the unit. For engineering purposes, I have used only pounds-mass and SI units.
When I taught physics, I only used SI units. None of the physics textbooks that I have seen over the last decade have used anything other than SI units.
I’ve never heard of the slug as being any more than a historical curiosity. FWIW, the unit is not even mentioned in the supplied reference book for the NCEES Fundamentals of Engineering (FE) exam.
FWIW, I used slugs extensively in both fluid dynamics and fluid design. I finished my undergrad about three years ago.
I’m quite surprised to hear this.
To convince myself that I’m not misremembering things, I just pulled out my copy of Unit Operations of Chemical Engineering, 4/e, by McCabe, Smith, and Harriott, published in 1985. This book was the text I used as an undergrad for fluid mechanics (among other topics). Slugs are not even mentioned in the text. There is an introduction to the SI system, as well as what the author calls the FPS (foot-pound-second) Engineering system. In this section, the author discusses the necessity of defining g[sub]c[/sub], called the “Newton’s-law proportionality factor for the gravitational force unit.”
However, that being said, I’ve also got an introductory book on fluid mechanics (published in 1999) that I picked up in grad school that only uses the SI system, and what the author calls the “British Gravitational” (BG) system of units. The text goes on to state that the book will not use g[sub]c[/sub] because it is unnecessary in the SI or BG systems.
So I guess the upshot is that it depends on the textbook and the instructors as to whether slugs are still used.
However, I’ll note again that the unit is not mentioned in the supplied reference book for the NCEES Fundamentals of Engineering (FE) exam. Only SI units and pounds-mass are used.
Got my undergrad in 1989.
Huh. Looking at my own 20-year-old FE (EIT, then) manual, it seems to be nearly exclusively in lbm, reserving slugs for the “English gravitational system.”
However, my old dynamics, fluid mechanics, and design books all use slugs preferentially. So, as you say, it probably depends on the preferences of textbook wrriters, and the preferences of the professors who choose the textbooks.
This is bizarre. I learned g[sub]c[/sub], but not as multiple variations you look up on a table.
g[sub]c[/sub] is in units of (ft-lbm)/(lbf-s[sup]2[/sup]).
I was orginally taught that F=ma needed to have g[sub]c[/sub] added, and then g[sub]c[/sub] for SI was 1. But found that a confusing way to look at it, and unnecessary. g[sub]c[/sub] is just a conversion factor to convert from lbm to lbf. That’s all it is. Like any other units conversion factor, you plug it in when you need to convert between those two sets of units. And yes, all the appropriate units are a necessary part of the conversion factor.
I will agree, but think it important to always include the units. That’s one of the double checks you have to ensure you did the math in the right order. Just because the SI units work out neatly without needing an extra conversion factor doesn’t mean you’re any less likely to accidentally invert an operation (flip the numerator for denominator). It also helps keep straight all those powers of 10.
Looking up factors on a table (especially ones that don’t have units) seems a sure fire way to miss your errors.
I’m not familiar with a Gc table; I learned it the way Irishman described; specifically, I remember it in the context of “showing all work” when writing out conversions for homework. In my work, I frequently see F=ma carried out where F is just in lbs.; however, there’s often a Gc (no units or other notation, just the “Gc”) written in the equation.
I also remember encountering slugs as a unit in homework problems. I graduated in December 2006, in case anyone is wondering.
This is interesting. I’m an engineering student in Canada, and we are learning both the SI system and what I assume is the food-pound-second system robby mentions, with slugs tossed in occasionally when the questions were worded that way to begin with. I have never heard of Gc. All of my profs have been very good about stressing the importance of showing unit conversions, so I guess things just get taken care of by doing the math properly in the first place!
Many dialects of SQL use <> as not equals. It’s not just Basic*.
There’s also the ever popular ~= or the old keypunch symbol that looks like a hypen with a tail hanging down from the right end. That symbol followed by = was not equals in PL/I. IIRC there are a few older oddballs (SNOBOL anyone?)which use |= as not equals as well.
I don’t remember much discussion or consternation over foot-pounds, slugs, and the like in my fluid mechanics class. Given, though, that I took it almost 10 years ago, I can’t say I remember much of anything from fluid mechanics.
I’m really curious if my students are learning all SI or have to deal with this too. Most of them are currently also taking fluid mechanics. I think I’ll ask around tomorrow, but I have the sneaking suspicion that they’ll look at me like I have three heads. (They do that enough as it is!) Based on how upset they were when I used gallons in class the other day, I’m thinking they actually haven’t had much exposure to engineering in non-SI units. Come on, guys, how else are we gonna do calculations related to the fuel economy of US cars?
I just realized it may be due in large part to the fact that my fluid and thermal design instructors used to work in the oil fields. Those petroleum guys mix units as much as explosives guys (cal/g? WTF?).
What’s so odd about calories per gram? They’re neither of them SI, but they’re both metric, and given that a calorie is defined in terms of the heat capacity of a gram of water, that seems like a perfectly sensible unit to me, in the right context at least.
Pascal uses it, too, but there’s a chance they all got it from BASIC: The first version of BASIC was created in 1964, years before both Pascal and SQL.
This looks more like ‘approximately equal to’ or the Perl-derived ‘regex match’.
The symbol is actually the logical NOT operator. It isn’t in ASCII so it wasn’t used in many languages after PL/I’s time. Maybe Unicode will revive it.
We could go back to the old FORTRAN conventions and use .NEQ. for this purpose. 
Oh, and another one I saw in some programming language or another: /= , which is supposed to look like ≠ .
I agree completely. Saying “You always have to add g[sub]c[/sub], but g[sub]c[/sub] = 1 for SI” is ludicrously backwards.
Force = mass times acceleration.
If instead of telling you the mass, I tell you the object’s weight under standard gravity, then you need g[sub]c[/sub] to convert from weight to mass.