Discussion in 'The Lounge' started by retrofit, Dec 1, 2020.
You are a real scientist, I’m just a scientist on paper
From the formula I would guess that sodium bicarbonate could be called sodium hydrogen carbonate, indeed it might be more logical to do so. But why change a name that every one learnt in school for at least the last 100 years. I suppose that by 11967 the new name might stick!
Argh, bloody fat fingers! 1967...
The problem facing the standards bodies is that many people are used to the pre-standardised terminology and, as the world’s governments will soon find, it is much easier to create a popular error than to correct it. With SI units my problem, if that’s the right word, is that naming derived units can actually reduce understanding. Take frequency as an example, the SI unit is Hertz, but cycles per second is much more descriptive. Likewise pressure, of course it is nice to honour Pascal but pounds per square inch or, if you must, Newtons per square meter, contains the details of what is really being described, force over area. Which is most useful, 1013.25 mB, 1013.25 hpa, 29.92 in Hg or 14.7 psi? Without knowing the derivation of the unit, calculating, in this case, force in comprehensible language becomes difficult.
Using scientific data to produce real world effects needs to be simple, if I want to tell someone why opening an aircraft door at altitude isn’t going to happen it is much easier to used differential pressure in psi and the door area in square inches and then convert to kilograms. Most people can’t envision a newton but a pound or a kilogram is something everyone can get their head around. Science shouldn’t be about obscuring information it should be about revealing it. Unfortunately, as someone who grew up in a world before derived units had names, I find the SI practice less than helpful.
Psi is not much use in a country which uses the metric system, and SI units. I know what it means, but my kids don't - we changed to the metric system in 1976, and they were born after that.
Interesting, I heard some TV programme a few days ago referring to a Newton, or is it a newton?, and realising that despite having a degree in Natural Sciences /Engineering, I really had no clue what a Newton (newton) is. Is it the force of an average sized English apple falling around 10 feet? I've really no idea!
(But I could work it out... if it was that important to me.)
Pounds, kilograms, and grams are units of mass.
Poundals, newtons, and dynes are units of force.
Weight is a force. The weight of a mass is dependant on the local acceleration due to gravity.
Its all perfectly simple.
Of course it is, if you happen to be scientifically biased. Unfortunately, in case you hadn’t noticed, the majority of the population aren’t scientifically biased and in many cases little interested. However, given a simple explanation almost everybody can understand the concept of the force exerted by a 1Kg mass under earth gravity. Very few people can do the same using newton’s.
If the intention is to turn Mr/Miss/Mrs average off science the practice of naming derived units is doing an excellent job. Have you noticed that weather charts simply state pressures as numbers? Charts published for general consumption rarely quote units. Indeed ask a random stranger whether 998 on a weather map is high or low* and you are likely to be met with head scratching.
As an engineer I am used to working with mixed units, as should be a photographer, but can you tell me what the pressure in your tyres should be in hpa? I suspect the average person remembers the numbers but ignores the units. My suspicion is that we choose the units that result in convenient size numbers, 35,000 ft sounds high, 10,000 metres less so. Units on a human scale are more comprehensible than larger or smaller ones. Over time we can, and do, get used to other units.
*998 is neither high nor low until it is related to the surrounding atmosphere. However 998 is below the ISA standard of 1013.25.
If your not already familiar with the units 14.7psi won't get translated to 14.7 pounds per square inch, so it's no more obvious than 101 kPa, Few would gain anything for having it written out longhand as 101 newtons per square metre either.
I work with compressed liquid & gases as well as occasionally vacuums so am reasonably familiar with both these units as well as bar & mmHg (millimetres of mercury).
PSI tend to give more convenient numbers over the pressure ranges I use (typically 5-6000psi) so it's still the unit I use most, with mmHg often taking over for vacuum. I have met one instrument manufacturer where the default pressure units were 'kilograms force per centimetre squared' which has always struck me as particularly odd mixing both cgs & MKS versions of the SI system. Fortunately I only need to track changes in pressure on this so the units were really irrelevant - 160 last week & up to 345 today something must be getting blocked!
My limited experience of American customary units or imperial units shows that they frequently have multiple units for measuring the same thing & these units are rarely nice convenient factor of 10 different. Just look at length where we meet point, inches, hands, feet, yards, fathoms, miles, leagues... (I've just listed those I've known used there are yet more)
Switching these to area & volume introduces even more units, and stupidity like a US dry pint being bigger than their liquid pint.
Yet more confusion is created by the US & UK imperial units frequently using the same name but having significantly different sizes (20% difference in the size of a gallon)
Even with named derived units the SI version is much simpler, and there are a few like Ohms where using the base units (kilogram metre squared per second cubed amp squared) only complicated matters completely
I'm fairly sure I have seen a water-gauge marked in acre-feet, just what you need to wet a field.
I agree that SI units are easy to work with but the derived units don't, to my mind, encourage understanding by the lay person. I think science should be accessible and I don't think derived units being given names is always helpful. I will accept that some are really helpful, like Ohm and Amp but then few people have a clue about those anyway, characteristic impedance floors even good engineers*.
Like you I think in terms of PSI for some things, Oxygen systems at around 1,500psi, Hydraulics at 3,000, 4,000 or 5,000psi and barometric pressure in mb or hpa. That however is part of my point, we chose the units that we are comfortable with.
(I had a colleague, and avionic specialist, who couldn't get his head around why an RF cable wouldn't work when a continuity check was OK! I got the technicians to hang in a replacement and everything worked. The cable had original been bent too tightly)
Not too many out of the science and engineering world (or STEM) understand the use of the Greek alphabet either.
mu for coefficient, delta for change in, and omega for angular (all used in our braking formula)
For me, I didn’t study newtons laws until college, but naturally I work with tools (of different kinds lol) so the N.m (torque wrenches) and machines rated for clamping forces in N, is something I see everyday.
We use a testing rig that has weights labelled in Newton’s instead of kilograms.
Or resistance (electrical).
Yes, I’d say the symbol for the ohm is the one most are familiar with.
Alt+224 Alt+225 correctly types αß in Notepad but does not work with Mozilla.
How do you get Greek letters without copy and paste?
Alpha Α α
Beta Β β
Gamma Γ γ
Delta Δ δ
Epsilon Ε ε
Zeta Ζ ζ
Eta Η η
Theta Θ θ
Iota Ι ι
Kappa Κ κ
Lambda Λ λ
Mu Μ μ
Nu Ν ν
Xi Ξ ξ
Omicron Ο ο
Pi Π π
Rho Ρ ρ
Sigma Σ σ
Tau Τ τ
Upsilon Υ υ
Phi Φ φ
Chi Χ χ
Psi Ψ ψ
Omega Ω ω
I pretty much copy paste, then the arduous task of rescaling for assignments.
Also, lambda is used on MOT certs for emissions I think (gas laws) and the symbol λ is used in the game half life
Well this is all Greek to me.
or the end (biblical)
Is this any help? It is old but looks useful http://www.alanwood.net/unicode/firefox.html. Link toward the end gives the unicode keystrokes for everything. http://www.alanwood.net/demos/ent4_frame.html
Separate names with a comma.