Why So Many Units?

useful to compare cars directly while saying nothing about what you really care about, cost.

You are thinking like some sort of scientist or engineer. Lord, no one car es about Newtons! They care about Wh/mi which is exactly what you wrote ab ove. Wh into the battery, miles out, Wh/mi.

Try asking anyone driving or better yet, selling electric cars and see if t hey know anything about Newtons.

Not for me. $0/kWh is zero no matter the scale factor. Besides, electric rates are much less volatile than gas prices.

eful as joules/mile or more commonly, even if not SI, kWh/mi. Of course th ese numbers will be related to driving patterns, but not the huge, direct i mpact that newtons suffer, just the same smaller effect we are used to with MPG.

Good for you. You've mastered SI units. Do you have your gold star? Unfo rtunately you're left out of the crowd because no one cares. Wh/mile is th e standard measure of the fuel economy of EVs. The US tried with some sort of totally bogus metric called MPGe. I forget exactly how it is calculate d, but it attempts to relate EV efficiency to gasoline in a pointless manne r. $/mile is what users actually care about. That is less than half the r ate of gasoline even taking into account cold climates and non-motive uses of the energy in the battery. I charged at home recently because I haven't been making trips with the virus running around. I pay about $0.07 per kW h which nets me around $0.02 per mile summer, $0.03 per mile in winter. Ga soline runs me around $0.10 per mile with the current low prices of gasolin e. Even a hybrid will run $0.04 or $0.05 per mile.

Yeah, I'm sure Tesla can tell you all about the Newtons of their cars.

...[half dozen units for pressure]

Sometimes, you just want a unit that fits the problem well, like Smoots for fraternity distance measure.

I've been experimenting (in the era of days-between-shaves and hiding behind a mask) with shaving products. There's a goo called 'brushless shave cream' that works well in a shower, because you can flush your face with water and use a washcloth to get it all off.

The proper quantity of the slime to use for a shave is between two garden slugs, and one-quarter banana slug.

What's the unit for heat rejection as in aircondition outside the US? We use BTUs and Tons. Never seen a conversion chart or found a spec sheet for aircoditioners not meant for the north american market.

The same as for most other energy flows - kW.

That matches the assumption that toothpaste is intended to be squeezed out for the length of the bristled part of the brush. Thus if the tube has a wide mouth everyone will use more toothpaste and thus buy more...

one cares about Newtons! They care about Wh/mi which is exactly what you wrote above. Wh into the battery, miles out, Wh/mi.

Strangely, lifejacket buoyancy is specified in newtons. Sometimes they even have dinky batteries...

Kilowatts.

eg:

More prevarication snipped...

No, it's miles that no-one cares about. Civilised countries barely even remember those.

The point of my entry into this thread wasn't to remind people what they already care about. It was to suggest a different way of thinking about things.

It still seems that you're immune to that.

And yet they should, because newtons are a direct measure of drag and other inefficiencies.

It's nice to know that Tesla's investors are paying your bills.

But entirely irrelevant.

CH

that would make sense, but I see many rated in btu/h I'm guessing because they come from the same factory making them for the US market

I found that out when trying to buy a less expensive PFD on the Asian chann els. They don't bother with any US approvals and often don't even specify the buoyancy. But that make sense. Submerge a PFD and it will provide a f orce pushing to the surface.

I never did find a PFD that is actually adequate for me. I'm on the large side and when you do the math, the US adult size is not really adequate, ba rely keeping my head above the surface. My mouth is just an inch or so out of the water. The Chinese PFDs have even less buoyancy for the most part, but then their size tends to be less, so that makes some sense. Like many things, they don't address a foreign market.

cares about Newtons! They care about Wh/mi

I can differentiate a good idea from a bad one. The idea of inventing a ne w standard index to compare items is not a new thought. That's why I menti oned MPGe. Using newtons adds nothing to the measurement and moves further away from what people care about, fuel consumption. You might as well try to promote drag coefficient.

if they know anything about Newtons.

You still aren't getting it. You are thinking like an engineer. You have totally failed to explain in terms a layman would understand why using newt ons is better than using Wh/mi. That's one of the reasons why the Challeng er disaster ended the way it did. The engineers were largely unable to exp lain their thinking, saying a launch was ?away from goodness in the current database?.

Using newtons as a metric of EV efficiency would produce similar results in the car buying public. Why can't you see that???

You seem to fail to understand economics and contract law. A promotion was offered to sell cars many of which would not have been sold without. This helped to ensure the survival of the company. Don't talk about anyone pay ing my bills. I paid an awful lot of Tesla bills with my purchase, now the y are simply honoring their contract.

Nonsense. Torque measurements are not the same as a force applied over a distance.

It doesn't take, or produce 1 horsepower to hang 550 pounds off a bar 1 foot long for 1 second.

Please explain torque measurements. An inquiring mind needs to know.

Even if the 550lb is attached perpendicular to the axis of the bar and displaced from the center of the bar by 1 foot? Why not? I think it is called 1 ft*lbf of torque.

The work done to tighten a bolt goes mostly into heat. It's not recoverable. It takes *more* work to un-do a bolt. That's why nuts don't spontaneously fly off bolts.

Torque is measured in units of force*distance. So is energy. But a newton-meter of torque is not a joule. Torque is neither power nor energy, it's just force.

You can hang a big weight on the end a long torque wrench for a hundred years, and nothing happens.

one could speak the same language? On this ventilator I am find many ways of expressing the same pressure and flow rates.

me field really. People just like to use different units.

sed to be Nm. I am always converting Nm, Ncm, ft-lb, in-lb., oz-in., etc.

worse. Units can be mass-per-volume or number-per-volume. Depending on th e industry we are serving, the preferred units are different. It gets a bi t obnoxious constantly converting mg/mL to nanomolar (for instance). Since our software analysis needs everything in molarity, I am often scrambling to find the molecular weight of this that and the other thing. And that is just the metric units!

and metric. We understand metric just fine, we just also happen to know a bunch of other units and know how to convert between them.

The measurement of torque is not the same as a measurement of energy, but t he units are the same... because if you rotate 1 radian against a torque of n Nm you will do n Nm of work. The 1 radian is dimensionless.

It only takes a moment to understand this if you consider the definition of a radian.

e could speak the same language? On this ventilator I am find many ways of expressing the same pressure and flow rates.

field really. People just like to use different units.

ed to be Nm. I am always converting Nm, Ncm, ft-lb, in-lb., oz-in., etc.

orse. Units can be mass-per-volume or number-per-volume. Depending on the industry we are serving, the preferred units are different. It gets a bit obnoxious constantly converting mg/mL to nanomolar (for instance). Since our software analysis needs everything in molarity, I am often scrambling t o find the molecular weight of this that and the other thing. And that is just the metric units!

nd metric. We understand metric just fine, we just also happen to know a b unch of other units and know how to convert between them.

wrap a rope around a cylinder with 1 meter radius, pull on that rope with the force of 1 Newton, that is 1Nm of torque, pull on the rope with 1 Newto n until you have unwound 1 meter of rope and you have done 1 joule of work

both are 1 newton and 1 meter but there is a difference

Yes, the distinction between work (force applied dot-product to displacement) and torque (force applied circumferentially on a lever arm radial from the center) means that torque can happen with zero work. But, the units are the same (and scaling torque to another units system doesn't require the dot-product selectivity of the force and displacement directions).

You have done your joule by pulling 1 Newton through 1 metre. The cylinder or its size is not relevant.

As whit3rd explained by introducing dot-product, it is whether the metre is measured along the movement of the force, which is work, or at right angles, when there is no implied movement or work, that makes the difference.

Mike.

That's a Yotta Units.

Here's a few more