slug vs. lbm - Dynamics (What the MERM doesn’t tell you)

[@alexfontaine6233]

Thanks man I'm in engineering school right now and this helped me out immensely

[@drtomsclassroom]

Alex, I am so glad. You can't go wrong with "slugs." All the best. Tom

[@map2mark]

I loved this Dr. Tom. I'm a ChemE who retired and now teach engineering and chemistry in a high school..... love it. I dodged this issue 40 years ago by going the ChemE route. Now I'm teaching mechanics to some aspiring engineers and got tripped up by the text book I'm using. Thanks for clearing it up!

[@drtomsclassroom]

So glad that you found the video helpful!

[@drury2d8]

This can catch even the most seasoned engineer, off guard. Signed off on a design that called for unrealistic structural enforcement. 3/8" plating for otherwise 10 gauge sheet steel. Re-ran the calcs in SI units and had to take the walk of shame with a dunce hat. Never gets old. Now, I have a picture frame of a slug on my wall.

[@FireLight275]

Fantastic, thanks for clearing up the Gc mess, Dr. Tom, finally someone I can relate to!

[@drtomsclassroom]

I am so glad this helped. This is the most troublesome issue in mechanics, those who will not accept "slug" as the unit of mass, but cling to "lbm" then need to arm wave away the problem with something called "gc." Where are you located and how did you come to watch this video? You have made my day. Thanks. Tom

[@FireLight275]

Slugs have simplified it, no more wondering when to use gc, I used to get so frustrated, esp since I used metric in my undergrad.. Thanks!

[@drtomsclassroom]

FireLight275 Slugs solves a great many problems. Why people still cling onto gc is beyond me. No gc in the metric system because everyone accepts Newtons for force. Everyone hates the term "slug." Tom

[@thandozuma8740]

This was stressing me... thank u Dr Tom

[@vafinest3234]

Still love this video never gets old

[@masonroush6259]

I kept getting things wrong by a factor of 32.2... Now I know why! and my professor said "we aren't doing slugs"

[@truthsurfer808]

Excellent video, this clears things up a lot!

[@tombrown2716]

Wonderful. Makes my day. Where are you located, and how did you come to view my video? Tom

[@truthsurfer808]

Hi Tom, I'm in Honolulu, HI. I found your video by doing a search for HVAC PE Exam on KZbin and first found your ME PE Exam Strategy videos which were excellent as well - then browsed your channel and found this gem. I agree with you, if only someone had originally chosen a different word than slug, it probably would have actually gotten used and not swept under the rug. After watching the strategy videos I'm a bit bummed out that I chose the HVAC PM portion instead of Thermo/Fluids, but I'm already registered, so I'll just have to give it my best and tackle it. Thank you very much for the videos!

[@tombrown2716]

God's Will be Done Wow! Honolulu! Is that you on the surf board? I have a participant in Honolulu that is taking the Online Only course for the April Exam. He wanted to attend the Live & Online, but he could not get permission to attend when it is 7 pm EST. He says if he passes, he is going to put my wife and I up somewhere. I will definitely be praying for him on Exam Day, and I can for you as well. Thanks for the information. Tom

[@truthsurfer808]

Yep, I moved out here from Florida about 4 years ago to pursue my passion for surfing in my free time. That's me surfing in the profile picture. The time difference from the mainland always messes us up over here haha! That would be great if you would put in a good word for me with the man upstairs. God bless. -Andy

[@danielcervantes5578]

Now, you know what you talking about. I been researching the internet and books for the past four hours and it seems nobody really knows the background. But this made it super clear. I do have one question in heat transfer when talking about btu/lbm, is the 'lbm' a unit of weight or mass? Why not just 'lb'.

[@drtomsclassroom]

In Thermo and Heat Transfer "lbm" is taken as mass, as those working in those areas have never warmed up to "slug." Fortunately the conversion 32.2 lbm = 1 slug never comes into play like it does in Mechanics. And keep "lbm" and "lbf" as they distinguish whether they mean "mass" or "weight", even though it is the same value. A 100 lb weight (lbf) has a 100 lb mass (lbm). Adopting "slug" would make things so easy and consistent with the SI System. Glad my video helped. Made my day, as this is probably the most unnecessarily confusing topic I teach.

[@danielcervantes5578]

drtomsclassroom thank you so much!! Most of my professors just tell you to divide by 32.2 without telling any background. Not sure if they do it to save time in class or they truly don't know lol

[@CartersvilleEngineer]

Excellent video

[@apetroleumengineer6973]

Referring to summary of this video, when we say density of water is 62.4 lb/ft3, it is mass density or weight density?

[@annakquinn7084]

Pound mass

[@JonBxd9]

On the slide that begins around 5:20 why are you using lb instead of lbm or lbf in your units to explain the slug???

[@JensenPalmer]

That is one reason that I am not excited to work with various people in industry (or anyone really) because of units and the non-standardization of it all. I am an advocate for both systems (SI and US Cust.). They each have advantages and disadvantages. Plus, so many people use kilograms as a unit of weight ("I weigh X amount of kilograms." No, you don't. You weigh that times the gravitational constant where you are, i.e., Newtons.) and then get on US Customary's case about it being confusing. People DIE because others can't get simple, stupid units right.

[@drury2d8]

Sorry, the British/Imperial system needs to be abolished.

[@brandonpeterson6306]

If only somebody could come up with standard international units without these stupid extra factors

[@tombrown6227]

Actually, they do for the SI/Metric system. It uses "kilograms" for mass and "Newtons" for force. No "gc" needed. 1 N = 1 kg m / sec^2. However, the US Customary system still needs "gc" because they want to use "lbf" for force and "lbm" for mass so that 1 lbf = 1 lbm x 32.2 ft / sec^2. If they would just use "slugs" for mass (I know it is a terrible name) then 1 lb (no "f" or "m" needed) = 1 slug ft / sec^2. No "gc" needed. Unfortunately, I appear to be the only one on the planet who wants to use "slugs", but at least I don't make 32.2 errors and have my design 32.2 times too big or 32.2 times too small. People will notice!!! Dr. Tom

[@brandonpeterson6306]

@tombrown6227 thanks, but I was joking! I know how to do all this in metric and it makes perfect sense. My frustration is that we (USA) won't bite the bullet and convert (pun intended) to metric

[@tombrown6227]

@@brandonpeterson6306 I figured you did by the tone of your post, but I wanted to get the story behind the problem out to those who might not know. Dr. Tom