When it comes to insulation temperature rating, why do we use celsius?

retirede said:
The real question why does Fahrenheit still exist at all?
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Fahrenheit is human-centric
Celsius is hydrocentric
Kelvin is physics-centric

Fahrenheit has the advantage of representing typical climate temperatures on a 0 to 100 scale, where 0F is about the coldest you generally expect an average location to get, and 100F is the hottest you generally expect an average location to get. It represents the range of climate temperatures where most people can survive, with the neutral point of comfort about 2/3 of the way through the scale. Not at half, because of the nature of heating being a significantly easier problem for our bodies to solve.

Fahrenheit does get you slightly improved precision, when representations of temperatures are limited to whole numbers. With Celsius, the upper half the 0 to 100 scale is too hot for people to survive, so half of the 2-digit number scale is unusable for most weather maps.
 
zbang said:
But they'd say "178 cm or 74 kg", same as most people would say they're "a little shy of 220 pounds" (or "half over 15 stone"), not that they're 218.4 pounds.

The fallacy of most units arguments is trying to make them exactly equal and then saying "that's too complicated!!!"
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Making them exactly equal isn't my point; even if they said 178 cm and 74 kg I would still have to figure it out. Most people have a good idea of what six feet looks like, but I would hazard a guess that far fewer of us can readily visualize 183 cm or even 180 cm. I had a lot of chemistry classes, so I have a better feel for ml and grams.
 
Carultch said:
This is the first I'm hearing that a "square rod" even means any specific size. And I know the rationale behind the definition of an acre, as strange as it always sounded to me, that an area unit wouldn't even be a square number of square distance units.
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If it helps, an acre is a little more that 670.5 square cubits.
 
ggunn said:
Making them exactly equal isn't my point; even if they said 178 cm and 74 kg I would still have to figure it out. Most people have a good idea of what six feet looks like, but I would hazard a guess that far fewer of us can readily visualize 183 cm or even 180 cm. I had a lot of chemistry classes, so I have a better feel for ml and grams.
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I think in "metric feet" [30 cm] and "metric inches" [25 mm] all the time, when I do drawings for the rest of the world. I aim either for the nearest centimeter, or the nearest 2.5 cm ("metric inch") to make dimensions easy for the builders to follow.
 
The thing that is nice about SI vs imperial units is the self consistency when considering physical law equations.

Consider acceleration. F=m * A . In pounds, feet, and seconds you end up with a 32 floating in the equation somewhere. But in SI you just have kg, m, N, and s with no scaling factor.

Horsepower from lb-ft and RPM? Vs watts from Newton meters and radians per second?

Have you ever had to calculate the coil voltage of a motor with flux given in 'lines per square inch'? Nightmare.

The thing is, the selection of the base units for this self consistent system was arbitrary/political.

The unit of distance could have easily been the foot and you could still have a perfectly self consistent system of units. (My preferred unit of distance would actually be the light nanosecond, which is just shy of 1 foot.)

By definition, the inch is 2.54 cm exactly. I was thinking the other day that had the inch been 2.56 cm exactly, that conversion between fractional inches and mm would be really easy. It is a fast way to approximate the conversion. (Approximate 1 cm as 100/256 of an inch, and simplify. 1 cm ~ 25/64. 3/8 inch is 96/256 inch is approximately 0.96 cm (3/8 inch is 0.9525 cm exactly, but I can get 0.96 quickly in my head))
 
ggunn said:
Something I have always wondered is what the difference, if any, there is between a "foot pound" and a lb-ft.
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Foot pound is the wrong term. Imagine moving 1 foot away from 1 pound of weight.

The correct term is pound-foot. Which is 1 pound at a distance of 1 foot.

But American slang users may consiser you a snob/nerd when you use the correct terminology. Kind of like the issue of saying 220V when the proper term has been 240V for more than 60 years
 
If you apply a force of one pound pound over a distance of 1 foot, you've done one foot pound of work.

If you apply a force of one pound on a 1 foot lever arm, you apply one foot pound of torque.

Same units, different concept (energy vs torque). If both are being used in a single context, it is common to call one a pound foot and the other a foot pound, but I don't think there is any real standard about which is torque and which is work. I tend to use pound foot to mean torque and foot pound to mean energy.

In SI, the unit of energy is the Joule, and the unit of torque is the Newton meter. But a force of 1 Newton applied over a distance of 1 meter is 1 Joule of work.

An alternative argument: energy is force (dot) distance, torque is force (cross) distance. The dot product and the cross product are different things, so while both are pound (something) feet, since we don't actually say the (something), the difference is lost in the word foot pound (and equally lost in Newton meter), but they really are different units because of the (something) that is lost.

-Jonathan
 
jim dungar said:
Foot pound is the wrong term. Imagine moving 1 foot away from 1 pound of weight.

The correct term is pound-foot. Which is 1 pound at a distance of 1 foot.
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Yes, I agree Mr Mod., I remember those units from school physics. - I was about sixteen then. people But then I got in to my degree and it was all SI units. That said, many here still use Imperial, units especially older people.
 
jim dungar said:
The correct term is pound-foot. Which is 1 pound at a distance of 1 foot.
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Although "foot pounds" is easier to say and less stilted sounding than "pound feet" and it's simpler to change from singular to plural when spoken. When writing it, who cares? :D
 
Also, most people in this country know that 100 degrees F weather is hot but don't have any idea about 38 degrees C.
 
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