# Rant against unit of measure nazis, check your ignorance **URL:** \ **Category:** The BBQ Pit\ **Created:** [February 3, 2016, 7:03pm UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080 "2016-02-03T19:03:15Z")\ **Posts on this page:** 20\ **Page:** 4
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [February 10, 2016, 6:25am UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080/61 "2016-02-10T06:25:34Z")
> [@naita](#): > > A newton is the force necessary to accelerate 1 kg by 1/299792458 of the **speed of light** per 9 192 631 770 cycles of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom. > [@watchwolf49](#): > > \ … (9 192 631 770 cycles)[sup]2[/sup] … \ Ahem! (See added emphasis.) ---
**Author:** ![watchwolf49](https://avatars.discourse-cdn.com/v4/letter/w/e9c0ed/32.png) [@watchwolf49](https://boards.straightdope.com/u/watchwolf49)\ **Post date:** [February 10, 2016, 3:09pm UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080/62 "2016-02-10T15:09:25Z")
> [@naita](#): > > Ahem! (See added emphasis.) Are you _seriously_ nitpicking my nitpick … since when did Nazism have to be right? (But point taken, my apologies … ) HOWEVER … The speed of light is a scalar, force and acceleration are vectors … [sticks tongue out] … not as smart as we think we is, eh? ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [February 10, 2016, 4:20pm UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080/63 "2016-02-10T16:20:21Z")
> [@watchwolf49](#): > > Are you _seriously_ nitpicking my nitpick … since when did Nazism have to be right? (But point taken, my apologies … ) > > HOWEVER … > > The speed of light is a scalar, force and acceleration are vectors … [sticks tongue out] … not as smart as we think we is, eh? That the numbers indicate the magnitude of the acceleration in question is of course implicit as anyone with a modicum of quality education would grasp. But just to placate the less fortunate I’ll agree to clarify that it is a vector relationship with a simple **F** = m **a** (Man it was hard not to switch the bolding from a to m there to mess with fragile minds.) ---
**Author:** ![GargoyleWB](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gargoylewb/32/199_2.png) [@GargoyleWB](https://boards.straightdope.com/u/GargoyleWB)\ **Post date:** [February 10, 2016, 10:45pm UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080/64 "2016-02-10T22:45:04Z")
Behold the mighty [Bril](https://en.wikipedia.org/wiki/Bril_%28unit%29) and friends. Especially useful when arguing with the spouse over the best setting for the living room dimmer. Seriously, light and optics books are bound in the skin of suffering souls and written in the blood of demons. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [February 11, 2016, 4:22am UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080/65 "2016-02-11T04:22:54Z")
> [@scr4](#): > > I should have added: **weight** is the **F** in **F = m1 m2 / r^2**. Obviously it’s different from **m1** , and doesn’t even have the same unit. That is newtonian physics, which is a useful approximation but is outdated concept post relativity. The mass-energy of the earth moon system is less than the mass-energy of the earth and moon if they were infinitely separated, and a neutron star has less mass than the same number of baryons that are infinitely separated. That is not accounted for in Newtonian physics. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [February 11, 2016, 4:33am UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080/66 "2016-02-11T04:33:39Z")
> [@The\_Niply\_Elder](#): > > Wow. Just wow. How do you not understand this? Mass and weight are as different to each other as distance and velocity, energy and power, resistance and impedance, capacitance and inductance are to each other. They are physically and conceptually absolutely different entities from each other that cannot be assumed to be the same thing. This whole hilarious field trip into GR that you’ve taken just plainly displays how you don’t understand the slightest thing that you’re quoting. There isn’t a single equation in the entire of physics, whether it be classical, GR, SR, quantum physics, string theory that allows you to freely substitute weight and mass as if they’re the same thing, none. If you do, you will get nonsense results everytime. :rolleyes: Einstein and tests by Loránd Eötvös and the Eöt-Wash group and many others disagree with you. > **[Test of the Equivalence Principle Using a Rotating Torsion Balance](http://arxiv.org/abs/0712.0607)** > > We used a continuously rotating torsion balance instrument to measure the acceleration difference of beryllium and titanium test bodies towards sources at a variety of distances. Our result Delta a=(0.6+/-3.1)x10^-15 m/s^2 improves limits on... Weight is a measure of the force caused by consent acceleration due to gravity and is equivalent to a measure of the internal mass referenced in Newtonian physics even if the units slightly differ. The fact that it induces a crisis of faith for you and your steadfast insistence to protect 16th century scientific claims as absolute is validation that my original pit is valid. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [February 11, 2016, 5:03am UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080/67 "2016-02-11T05:03:48Z")
As an attempt to explain why gravity is an fictitious force, viewed through a frame of reference used to describe the force in accelerating compared that is assumed to be a non-accelerating frame [![]( " - YouTube") ](https://www.youtube.com/watch?v=aRDOqiqBUQY) If you notice how the puck is moving in a straight line from the non-rotational frame it should be clear that an object of any mass would follow the same straight line (unless friction becomes an issue in that demo) This is why the Newton or Slug is not the same as kilogram-force/kilopond or pound-force. These gravitational units of force do not relate to the force required to move an item but the force required to change their momentum away from their straight line. In spacetime a free fall is the shortest path (geodesic) and is where Einstein came up with the equivalence principle. The force observed in gravity is the earth accelerating you away from the shortest path in spacetime, not a pull to the earth. This is caused by the geometric property of curved space time, and it may be more intuitive to think of it as the force caused when the earth runs into you. Here is a good playlist from youtube that will try to explain it better for those of you whom want to try to understand it without learning the math. https://www.youtube.com/embed/videoseries?list=PLsPUh22kYmNAmjsHke4pd8S9z6m_hVRur&wmode=transparent&rel=0&autohide=1&showinfo=1&enablejsapi=1 Now if I could get the time back I wasted trying to find those videos. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [February 11, 2016, 5:16am UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080/68 "2016-02-11T05:16:36Z")
Cliff notes version of above if you only want to spend the time to watch one video [![](https://img.youtube.com/vi/NblR01hHK6U/maxresdefault.jpg "Is Gravity An Illusion?") ](https://www.youtube.com/watch?v=NblR01hHK6U) ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [February 11, 2016, 10:24am UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080/69 "2016-02-11T10:24:31Z")
> [@rat\_avatar](#): > > That is newtonian physics, which is a useful approximation but is outdated concept post relativity. > > The mass-energy of the earth moon system is less than the mass-energy of the earth and moon if they were infinitely separated, and a neutron star has less mass than the same number of baryons that are infinitely separated. > > That is not accounted for in Newtonian physics. And the mass-energy of the dinner plate - earth system is less when the plate is on the table than when the plate is on a high shelf, but that doesn’t change the mass of the plate, whereas the weight does change. It’s like you’re trying to outnitpick useful physics with a flawed understanding of general relativity. Do you also demand people tell you what reference frame they are using when they tell you their trip took three hours? ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [February 11, 2016, 4:14pm UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080/70 "2016-02-11T16:14:21Z")
> [@naita](#): > > And the mass-energy of the dinner plate - earth system is less when the plate is on the table than when the plate is on a high shelf, but that doesn’t change the mass of the plate, whereas the weight does change. > > It’s like you’re trying to outnitpick useful physics with a flawed understanding of general relativity. Do you also demand people tell you what reference frame they are using when they tell you their trip took three hours? The _intrinsic_ mass does not change, but the _inertial_ mass does change, which is what the kilogram measures. F=MA or E=MC^2 only applies in inertial frames, or in similar accelerated frames in the case of E=MC^2. The term mass is used in too many contexts but I am not confused. A flashlight in a light proof box will not lose inertial mass when turned on but a flashlight in free air will lose mass when it is turned on. The _mass_ that the KG measures will also be slightly higher for a compressed spring due to the higher potential energy, just as height as you defined above will effect it. It also will be sightly different if the arrangement of those elements change or if you try to compare it across dissimilar frames of references. But I am open to being educated here, show me that H20 doesn’t have less inertial/gravitational mass than 2\*H+O, or that two up and a down quark have the same inertial mass as a proton. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [February 11, 2016, 5:47pm UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080/71 "2016-02-11T17:47:01Z")
It is also funny how wikipedia has a Q&A section for this as an example. > **[Mass in general relativity](https://en.wikipedia.org/wiki/Mass_in_general_relativity)** > > The concept of mass in general relativity (GR) is more subtle to define than the concept of mass in special relativity. In fact, general relativity does not offer a single definition of the term mass, but offers several different definitions that are applicable under different circumstances. Under some circumstances, the mass of a system in general relativity may not even be defined. > The reason for this subtlety is that the energy and momentum in the gravitational field cannot be unambiguously l... > [@](#): > > _If two objects have the same mass, and we heat one of them up from an external source, does the heated object gain mass? If we put both objects on a sensitive enough balance, would the heated object weigh more than the unheated object? Would the heated object have a stronger gravitational field than the unheated object?_ > > The answer to all of the above questions is yes. **The hot object has more energy, so it weighs more and has a higher mass than the cold object. It will also have a higher gravitational field to go along with its higher mass, by the equivalence principle**. (Carlip 1999) GR is not easy, but we need to quit the practice of teaching people absolutes to just tell them “oops we lied” when they get to a more advanced topic. The confusion demonstrated in this thread is a good example on how it limits learning. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [February 12, 2016, 6:53am UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080/72 "2016-02-12T06:53:37Z")
> [@rat\_avatar](#): > > The _intrinsic_ mass does not change, but the _inertial_ mass does change, which is what the kilogram measures. F=MA or E=MC^2 only applies in inertial frames, or in similar accelerated frames in the case of E=MC^2. What unit would you like to measure intrinsic mass in? How about inertial mass? ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [February 12, 2016, 7:01am UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080/73 "2016-02-12T07:01:18Z")
> [@rat\_avatar](#): > > GR is not easy, but we need to quit the practice of teaching people absolutes to just tell them “oops we lied” when they get to a more advanced topic. The confusion demonstrated in this thread is a good example on how it limits learning. Bullshit. Hardly anyone needs an understanding of general relativity, and those that do have zero to no problem putting aside the “lies to children” they have to abandon when they start doing so. There’s two ways of accomplishing what you seem to desire. a) We can make all high school physics teachers mention as an aside while teaching F=ma that mass does change in ways that they’ll most likely never need to care about. This will either be ignored and forgotten, or confuse. b) We can teach general relativity in depth before doing anything newtonian. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [February 12, 2016, 7:12am UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080/74 "2016-02-12T07:12:02Z")
> [@rat\_avatar](#): > > But I am open to being educated here, show me that H20 doesn’t have less inertial/gravitational mass than 2\*H+O, or that two up and a down quark have the same inertial mass as a proton. That’s not the discussion you initiate in your OP or what people here are disagreeing with you on. H[sub]2[/sub]O has less mass than 2H + O. As a result the weight is also different. But if I move the substance to a higher shelf I will need less force to keep it up, in a way that has nothing to do with a change in any kind of mass. Weight is defined as that force, measured in the same units as other forces. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [February 12, 2016, 7:24am UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080/75 "2016-02-12T07:24:05Z")
> [@naita](#): > > What unit would you like to measure intrinsic mass in? How about inertial mass? intrinsic mass mass, like newtonian physics, is a fiction. Newtonian physics only holds true in an inertial frame, it does not exist in the real world. It is a useful approximation but it does not describe the true nature of the world. And despite your claim that people have no need to know how the world really works we would not be having this conversations without the laser optics used in network communication devices nor the transistors in the memory and CPU in our computers without people understanding the very _real world_ implications of QFT/GR. But this is a facetious argument, no one needs to know the difference between weight and inertial mass as it relates to a supposedly empirical claim of intrinsic properties of a fictional thought construct due to newtonian physics. Just look at how you shouted down my claims as being based in ignorance with such absolute conviction despite the fact _your_ claim was the one based in ignorance. The fact that you are still trying to conflate intrinsic mass with inertial mass indicates you still do not grasp the core concepts. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [February 12, 2016, 7:29am UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080/76 "2016-02-12T07:29:58Z")
> [@naita](#): > > That’s not the discussion you initiate in your OP or what people here are disagreeing with you on. H[sub]2[/sub]O has less mass than 2H + O. As a result the weight is also different. But if I move the substance to a higher shelf I will need less force to keep it up, in a way that has nothing to do with a change in any kind of mass. Weight is defined as that force, measured in the same units as other forces. If you put a substance on a higher shelf the inertial mass and the weight does change to a small amount but it is tiny. The mistake you are making is assuming that a measure of inertial mass is a measure of the “stuff” in something, it is not. Inertial mass being equivalent to gravitational mass (or weight) is the idea behind the Einstein equivalence principle. But be happy in your ignorance if you wish, I cannot fight blind faith masquerading as science. Please just quit parroting your ignorance to others as fact. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [February 12, 2016, 9:04am UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080/77 "2016-02-12T09:04:49Z")
> [@rat\_avatar](#): > > If you put a substance on a higher shelf the inertial mass and the weight does change to a small amount but it is tiny. The mistake you are making is assuming that a measure of inertial mass is a measure of the “stuff” in something, it is not. Inertial mass being equivalent to gravitational mass (or weight) is the idea behind the Einstein equivalence principle. > > But be happy in your ignorance if you wish, I cannot fight blind faith masquerading as science. > > Please just quit parroting your ignorance to others as fact. I don’t assume it is a measure of the “stuff” of something, but “Everything is actually mostly empty space” and “Mass is actually nearly all about the energy in a system of bound particles” aren’t particularly useful statements to understand the world. You keep railing against “blind faith”, but you’re also misrepresenting everyone discussing against you and you keep repeating the nonsensical “gravitational mass (or weight)”, when mass and weight _are_ _different_ things. Related things, but not the same. But maybe I’ve been indoctrinated with “lies” to the extent I’m unable to grasp what you’re saying. I’m willing to learn. Here’s how I would represent mass and weight to a fifteen year old who might eventually be a physicist, but is more likely to be a mechanical engineer or real estate agent: > [@](#): > > Objects such as me, or this chair, have mass. We measure this in kilograms, but most of our measuring devices actually report the weight of the object, which is the force required to counteract gravity. If I have an object with a weight of 10 N, then 10 newtons of force upwards will keep it still in the reference frame of the planet, whereas 20 newtons will accelerate it upwards by about 9.81 m/s^2. If I point the rocket sideways the acceleration will be 19.62 m/s^2. > > If I move my lab to the moon, the force needed to keep the object still will be smaller. A rocket with 20 newtons of thrust will give a higher acceleration upwards. But sideways the acceleration will sill be 19.62 m/s^2. > > The mass does not change, but the weight does. Later the student may encounter special relativity and general relativity and those who do readily grasp that newtonian mechanics, while useful in most everyday situations, has limitations. Now how would your lesson on how to calculate accelerations in everyday free fall situations go? How would you explain to a 15 year old about mass and force and their relationship to avoid conflict with general relativity? ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [February 12, 2016, 9:24am UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080/78 "2016-02-12T09:24:29Z")
> [@naita](#): > > I don’t assume it is a measure of the “stuff” of something, but “Everything is actually mostly empty space” and “Mass is actually nearly all about the energy in a system of bound particles” aren’t particularly useful statements to understand the world. > > You keep railing against “blind faith”, but you’re also misrepresenting everyone discussing against you and you keep repeating the nonsensical “gravitational mass (or weight)”, when **mass and weight _are_ _different_ things**. Related things, but not the same. Gravitational weight is a measure of inertial mass, the force expressed through that mass is due to the intrinsic property you shorten to mass. I don’t know how many times I can reference the _Einstein equivalence principle_ and you can just ignore it. The belief that it is difference is only because you were subject to a education system is teaching you 1865 concepts as “reality.” This _Einstein equivalence principle_ has been confirmed by every single experiment testing it ever attempted to date. It is reality and the only reason you think it is measuring something fundamentally is due to a failure to incorporate scientific concepts that are over 100 years old into the education system. I have provided cites but if you are just going to go off your base assumptions I will never be able to change your mind. To quote Tim Minchin > [@](#): > > Science adjusts its views based on what’s observed > Faith is the denial of observation so that belief can be preserved. What you are perpetuating here is faith, you stance is ignoring a century of scientific observation. When you measure weight in the presence of gravity you are measuring the _exact same property_ that would be measured on any balance. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [February 12, 2016, 9:27am UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080/79 "2016-02-12T09:27:36Z")
> [@rat\_avatar](#): > > And despite your claim that people have no need to know how the world really works we would not be having this conversations without the laser optics used in network communication devices nor the transistors in the memory and CPU in our computers without people understanding the very _real world_ implications of QFT/GR. I wrote that very few people require this knowledge, and that those who do suffer no harm by first learning the relationships that work well in other situations. > [@](#): > > But this is a facetious argument, no one needs to know the difference between weight and inertial mass as it relates to a supposedly empirical claim of intrinsic properties of a fictional thought construct due to newtonian physics. They do need to know the difference between mass and force to utilize all the very practical newtonian formulas for acceleration and energy. Feel free to explain how you’d teach the distinction, or non-distinction, between force and mass to high school students. > [@](#): > > Just look at how you shouted down my claims as being based in ignorance with such absolute conviction despite the fact _your_ claim was the one based in ignorance. > > The fact that you are still trying to conflate intrinsic mass with inertial mass indicates you still do not grasp the core concepts. I grasp that intrinsic and inertial mass are the same in every instance I need to use mass, and completely incomprehensible concepts in general relativity. I’m not trying to conflate them, I personally have no need to separate them. I do however need to work with force (including “fictitious forces” which may or may not include weight if one has an allergy to the very practical Newtonian mechanics) as measured in newtons and masses measured in kg. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [February 12, 2016, 9:35am UTC](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080/80 "2016-02-12T09:35:57Z")
> [@naita](#): > > I wrote that very few people require this knowledge, and that those who do suffer no harm by first learning the relationships that work well in other situations. > They do need to know the difference between mass and force to utilize all the very practical newtonian formulas for acceleration and energy. Feel free to explain how you’d teach the distinction, or non-distinction, between force and mass to high school students. > I grasp that intrinsic and inertial mass are the same in every instance I need to use mass, and completely incomprehensible concepts in general relativity. I’m not trying to conflate them, I personally have no need to separate them. I do however need to work with force (including “fictitious forces” which may or may not include weight if one has an allergy to the very practical Newtonian mechanics) as measured in newtons and masses measured in kg. Intrinsic mass is not a measure of inertial mass, if you need intrinsic mass you cannot use the inertial mass. But what is so hard about telling a student. a) Weight is a measure of the force exhibited by the inertial mass in the fictitious force of gravity. b) if you need to use it the Newtonian calculation F=MA is a good approximation. And do you realize that F=MA is not valid on the surface of the earth even under Newtonian physics? It is only valid in an inertial frame, so unless you let go of a ball and it doesn’t drop it is purely an approximation even if we were in a pre-Einstein world. If not I have news for you, you are not living in a Newtonian inertial frame. [Previous page](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080.md?page=3) [Next page](https://boards.straightdope.com/t/rant-against-unit-of-measure-nazis-check-your-ignorance/745080.md?page=5)