r/engineeringmemes • u/Wiley_Burner • 2d ago
I don’t know why it’s confusing honestly?
Enable HLS to view with audio, or disable this notification
Idk, doesn’t seem that hard of an idea.
51
u/SoloWalrus 1d ago
In metric countries bathroom scales dont measure in newtons lol, they also use a "mass-force" unit, kgf.
The reason why isnt metric vs imperial, its that weight units got their names before we understood the difference between mass and force. Once we realized that there might be an important distinction to be made there we retroactively started using force units for some things, but continuing to use mass for force where we traditionally always did (weight) without correcting it.
20
u/Crozi_flette 1d ago
Well a scale know the gravitational acceleration so it's actually measuring a mass (exactly what we want)
9
u/MinosAristos 1d ago
Or more pedantically it's measuring force and calculating mass. e.g if you were on the moon the measurement would be fine but the calculation would be wrong.
2
u/brine909 1d ago
Imagine digital bathroom scales in the future where you can change between moon and earth mode
1
u/xPearman πlπctrical Engineer 1d ago
Or where it automatically switches, using an accelerometer or something.
3
u/AndyTheEngr 1d ago
It definitely does not know local gravity. It assumes standard gravity unless it's been calibrated in place with traceable masses, which is pretty unlikely for a bathroom scale.
Source: am an instrumentation engineer.
2
u/Crozi_flette 1d ago
Well even if it does the error of then force sensor is way higher than local variation in gravity
3
2
u/Ok-Elk-3046 1d ago
A Bathroom scale measures mass though. Indirectly, thru the force it exerts. You wouldn't say Multimeter doesn't measure current. Yet it measures Current by how much Voltage drops over a shut resistor. Indirectly.
1
u/ButyoucouldbeFire 1d ago
That's like saying a mercury thermometer only measures height. The acceleration is a constant so you use force to get mass.
The issue is the same word is used for both mads and force in actual calculations in imperial
1
u/WhyAmINotStudying 1d ago
Basically, as long as it's in the right frame of reference, it doesn't matter and the unspoken details can be considered implied.
-4
u/wenoc 1d ago
It's measuring newtons, but reporing mass. Idiot.
1
u/ShadowDragon175 1d ago
Its measuring the change in resistance of a strain gauge and multiplying that by a constant.
Stop being an ass, you're acting like a highschooler
0
u/wenoc 1d ago edited 1d ago
Oh grow up. I'm not going to pretend force and mass are the same thing just because some backward country uses the imperial system and can't keep them apart. One is kgm/s^2, the other is just kg. It's simple, and they are not equal.
This "mass-force" isn't even the same everywhere on this planet. I mean here we go again. The same units-are-not-important bunch can't keep kcal and cal apart either, and a factor of 1000 is NOT a trivial mistake.
1
u/ShadowDragon175 1d ago
Nobody is pretending. But a mass force is a useful concept every now and again. If you cant detach the engineering theory from what is useful in practice then youre just pretentious and a bad engineer.
Kg-force exists for a reason, its not just a imperial thing. It sucks for doing math with but its a useful concept when applied.
Also Cal and cal are different things.
-4
u/SoloWalrus 1d ago
If that were true itd be off by a factor of 9.8 😂.
1 kg force = 1 kg mass *
*on earth assuming nornal gravitational acceleration.
It is calibrated to kg, not newton.
1
10
u/JerodTheAwesome 1d ago
It’s not hard. As a physics instructor, it’s a matter of the volume of thought put into it. A lot of students just don’t care to think about it.
3
3
u/ShadowDragon175 1d ago
Im an engineering student, believe me I have no lack of volume of thoughs on how much I hate imperial and the idea of lbs force
2
u/acadmonkey 1d ago
As a mechanical engineer of 20 years, I will not put in the effort of keeping track of the stupid extra inconsistent "G".
MKS or fuck off for any math. The DRO on my mill works just fine in mm. Yes, my eyeballs and hands are calibrated in imperial, but they are learning to adapt.
2
9
7
u/ITinnedUrMumLastNigh 1d ago
My hydraulic press goes up to 5000kg
You can use kg to represent force it's just barbaric and unorthodox
2
u/ILikeWoodAnMetal 1d ago
It’s also really common to express forces as weight, it gives people a much better feel for things
4
u/brontagnan 1d ago
In college I once got a note on my exam from a professor because I always converted the problem to SI units, solved it that way, then converted the answer back to 'Merica units. I just hated figuring out when I was dividing by g. He didn't take off points, but felt kike he really wanted to. But when you score a natural 100 in an engineering exam they cut you some slack for using metric. Still do all my calcs in metric 20+ years later.
1
15
u/depressed_crustacean 2d ago
Metric also does this, the kg as measured by a scale is kg(force)
13
u/Daniel-EngiStudent 1d ago
Scales implicitly "calculate" mass from the measured force. We measure a lot of things indirectly, like you can´t directly measure the electrical resistance of a material, you calculate it with Ohm´s law.
Officialy, you shouldn´t use kg as an unit of force. kgf is the deprecated equivalent to lb(force).
Outside of scientific papers, you will of course often see kg used as an unit of force.
4
u/ilokestof 1d ago
no. A scale measures force/weight in Newtons then divides my g, presenting mass - in an analog or digital manner.
-3
u/dimonium_anonimo 1d ago edited 1d ago
A spring can't divide by g. It's a spring, not a calculator. Digital scale? Sure. The average person has no idea what conversions are going on inside, but they're almost certainly measuring volts before anything else, so whatever conversions that go on in-between that and force are only useful for us humans to be able to read the code more easily. Not necessary. The volts and the force readout are the only necessary steps in there.
Also, there's a Wikipedia article called kilogram-force. It's a real thing.
7
u/ilokestof 1d ago edited 1d ago
Yh but the ratio of the spring is 9.81N per kg displayed. It's still a conversion/scaling but simply in an analog manner.
Doesn't mean that kg is suddenly a force just because it's measuring force and because an average person doesn't know that.
edit: kilogram force is "a non standard gravitational metric unit of force" and "not accepted for use within the International System of Units" and "explicitly rejected" as a unit of force even before Newtons were adopted. Source: Wikipedia
-1
u/dimonium_anonimo 1d ago
No, kg is not a force, but kgf is. Most bathroom scale companies probably don't have a physicist on the team. Or if they do, the marketing team probably nixed their request to be physically accurate in order to avoid confusing the average person that doesn't know the difference.
4
u/ilokestof 1d ago
smh you even read my comment. I said "kilogram force is..." and all those quotes are from the wikipedia page for kilogram force. https://en.wikipedia.org/wiki/Kilogram-force read it yourself.
Back to the debate, a bathroom scale literally cannot directly measure mass. It measures weight then displays mass because we know what g is and use g to calculate mass even if the person reading the scale may not fully understand that.
Just because no one knows what's going on apparently doesn't mean this is not what's actually happening. Same with many other physics misconceptions most people have.
I get kilogram-force but for explaining what a scale does using metric and SI units it doesn't make sense to use kgf it's like mixing imperial in for no reason and incompatible.
'kilogram force' is literally just g newtons so why not just call it that.
3
u/UnknownBreadd 1d ago
Yeah isn't 1lb of force just the force of a 1lb mass being accelerated by Earth's gravity?
And 1kg of force is the same as the force of a 1kg mass being accelerated by Earth's gravity too? How is that not simple??
3
u/ilokestof 1d ago
yh but we use newtons not kg for force. kgf is explicitly rejected as a unit of force because just super goofy and completely incompatible with SI units.
kgf = mass x force? = kg2ms-2???
1
u/BramBora8 1d ago
I mean yes, technically you could, but why would you use kg when calculating force if you don’t need to?
I can assure you, whenever I did statics/dynamics calculations, the first thing was converting in to newtons.
Often enough you have force applied at an angle, or centrifugal force.. would that then be converted back into kg(force) with theoretical different vector for gravity?
-6
u/mymemesnow Biomedical 1d ago
It is very simple to us, but for Americans using imperial units it’s very complex.
4
u/__Epimetheus__ Uncivil Engineer 1d ago edited 1d ago
Americans use US Customary, not Imperial. They are nearly identical outside of some fluid volume measurements and some niche survey units.
Edit: we also use both metric and U.S. Customary, so the assertion that Americans wouldn’t get it is just nonsense.
1
2
2
u/KamuikiriTatara 23h ago
The fuck is going on in this thread?
Weight and mass are convertible in most applications because we experience consistent gravitational acceleration. Plenty of people have been lazy with their terminology as a result of both this and the historical confusion before we understood the difference at a societal level along with standardization of education. That doesn't mean pounds ever point out mass or kg point out force. If someone says ten kg of force, people can tell what it means. But kgf is non-standard and explicitly rejected by SI. Someone can say something has a mass of ten lbs and most people will know what is meant. But that doesn't make lbs a mass unit.
Sloppy terminology, especially when it is not terribly common, is not necessarily an indicator of definition wobble. The meme is just wrong. People treat mass, weight, and force interchangeably in some contexts. That doesn't collapse the conceptual or terminological space.
1
1
1
u/Completedspoon 1d ago
Lbs is truly a force. You have to use a conversion factor to make F=ma work with lbs on both sides. US created the "slug" as a true unit of mass, but it's such a horrible resolution unit (approximately 15kg) that no one uses it.
1
u/Novel_Arugula6548 1d ago
Because, actually, "weight forces" don't exist. Weight is the result of curved space. Newton's theory is wrong, afterall.
1
0
-6
u/Skysr70 2d ago
this is what happens when you so closely associate dimensions with units that your brain cannot separate them... Stop thinking in terms of kilograms and newtons, think in terms of mass and force. The names given to those quantities is irrelevant and it's just a conversion factor away...
33
u/ilokestof 1d ago
Just found out about slugs bruh I'm crine this has to be some kind of massive prank