Metric/imperial

[Kertech]

I always find it weird listening to american news and even science shows where they talk about feet, pounds, farenheit. I was looking at xkcd today and I wondered, would a shift to the metric system make a difference or is it just semantics? (also in the UK we are taught metric in class, but our roads are in miles)

[p1t1o]

If you go to the wikipedia page on liquid oxygen, some genius asked in the "Talk" page:

"Why in an English encyclopedia are temps not in Fahrenheit."

Nearly made my eyes pop out.

[Nibb31]

These discussions don't end well.

Also I disagree with today's XKCD. The "lost a Mars probe" line should be in the Fahrenheit list, not Celsius

[YNM]

Living (born, in fact) in the metric-ized part of the world, using (or thinking) in miles or fahrenheit isn't much of a problem thanks to 5:8 rule wrt metric and the fact that human body temp is around 100 F (water freeze at 32, knew it). But get me over to anything else and I have zero clue about it. Metric is helpful because the scale are base ten - compare to bottles (volumes), what the heck are fl.oz, or anything else ? Also, haven't nailed pound - kg and pound - newton conversion (got no clue whenever people talk of engines in imperial).

[sevenperforce]

The Imperial system was based around powers of 2 and 3 rather than powers of 10 in order to streamline mental arithmetic and mental fractions. There are 8 fluid ounces in a cup and 6 teaspoons in a fluid ounce...which means if you're changing the proportions of a recipe, you can subdivide to pretty much any fraction you want without needing to use a calculator. And yes, it's wonky to have exactly 5280 feet in a mile, but if you're surveying land without fancy laser rangefinders then it's nice to be able to split a mile into 2, 3, 4, 5, 6, 8, 10, 11, 12, 15, 16, 20, 22, 24, 30, 32, 33, 40, 44, 48, 55, 60, 66, 80, or 88 equal segments without having to get into fractions of feet.

[p1t1o]

Whilst I am a strong metric proponent, its funny how Celcius:Farenheit/Imperial:metric is always is a bit of a debate but when it comes to car engines, the vast majority of us [myself included] would be all like "Welp, clearly we should should be comparing this to a good strong horse!"

[Budgie]

1 minute ago, p1t1o said:

Whilst I am a strong metric proponent, its funny how Celcius:Farenheit/Imperial:metric is always is a bit of a debate but when it comes to car engines, the vast majority of us [myself included] would be all like "Welp, clearly we should should be comparing this to a good strong horse!"

I may be mistaken, but doesn't a single horsepower compare to a rather sickly and weak horse?

Ultimately, I see the sense in both systems and a total conversion would be unfathomably difficult. I was raised in Imperial/US, but metric makes more sense to me personally and I'm trying to get to the point where I can estimate and use both systems equally.

[Kerbart]

I'd argue that it's to a large extend semantics. As pointed out above, both systems have advantages and disadvantages. I think that metric is easier in scientific and engineering applications when quantities, expressed as a fraction from each other, don't need arcane conversion factors just because you're switching from inches to feet or from ounces (solid or liquid) to pounds, especially when squares come in place.

For day to day life it doesn't really matter, which is why metric has such a hard time being adopted in the US. There's no real advantage for Joe Average to use centimeters over inches, and switching over is a major inconvenience for 90% of the population. There are long term advantages in science and engineering. But those are things we really don't like that much in the US, as a society. So why bother?

[p1t1o]

9 minutes ago, Budgie said:

I may be mistaken, but doesn't a single horsepower compare to a rather sickly and weak horse?

Ultimately, I see the sense in both systems and a total conversion would be unfathomably difficult. I was raised in Imperial/US, but metric makes more sense to me personally and I'm trying to get to the point where I can estimate and use both systems equally.

After a quick gander at the wiki, it doesn't seem to specify much about the horse, seems more to be based on a task that an average horse can do (such as lifting a weight with a pulley), rather than its max theoretical output. More confusingly, there are many different standards for horsepower, including a "metric" and an "imperial" one. And also interestingly, it is quoted that an average human can briefly output 1.2hp, and 0.1hp indefinitely, and a trained athlete 2.5 and 0.3 respectively.

 

And I agree with those saying the differences barely matter day-to-day, but it still makes sense for there to be a global shift to a harmonised, science-based system.

[PB666]

48 minutes ago, Kertech said:

I always find it weird listening to american news and even science shows where they talk about feet, pounds, farenheit. I was looking at xkcd today and I wondered, would a shift to the metric system make a difference or is it just semantics? (also in the UK we are taught metric in class, but our roads are in miles)

Actually for physics the units should be:

• the gravitational constant, G,
• the reduced Planck constant, ħ,
• the speed of light in a vacuum, c,
• the Coulomb constant, 1/4πε₀ (sometimes k_e or k), and
• the Boltzmann constant, k_B (sometimes k).
• L = 1.616199(97) × 10⁻³⁵m
• M = 2.17651(13) × 10⁻⁸kg
• T = 5.39106(32) × 10⁻⁴⁴s
  [Note the lack of precision in the above units is due to uncertainty in the universal gravitational constant]
• Q = 1.875545956(41) × 10⁻¹⁸C
• Θ = 1.416 833(85) × 10³²K

Every other measure in the universe is subjective.

With these measures

E = m   (c = L/T)

E² = m² + p²

E = v  (wavelength)

F = m¹m²/r

F = q¹q²/r

22 minutes ago, Budgie said:

I may be mistaken, but doesn't a single horsepower compare to a rather sickly and weak horse?

Ultimately, I see the sense in both systems and a total conversion would be unfathomably difficult. I was raised in Imperial/US, but metric makes more sense to me personally and I'm trying to get to the point where I can estimate and use both systems equally.

I think its a measure of average daily production of a draft horse, its not the output of a racing horse at full run just before its heart blows to bits. Even though cars are rated like this, when you want to buy a car you really should be looking at torque at a certain RPM, say 2000 to 2500. Then use that to determine the effective strength of the engine, in most cases you need acceleration when the car is not moving and the engine is moving near its idle, the only time you see full horsepower is when your car is at close to maximum speed in a gear lower than the most efficient gear for that speed.

[kunok]

40 minutes ago, p1t1o said:

Whilst I am a strong metric proponent, its funny how Celcius:Farenheit/Imperial:metric is always is a bit of a debate but when it comes to car engines, the vast majority of us [myself included] would be all like "Welp, clearly we should should be comparing this to a good strong horse!"

That's only because tradition, in the new electric vehicles KW are commonly used, at least where I looked.

[Bill Phil]

Thing is that it doesn't matter.

[mikegarrison]

1 hour ago, PB666 said:

Even though cars are rated like this, when you want to buy a car you really should be looking at torque at a certain RPM, say 2000 to 2500. Then use that to determine the effective strength of the engine, in most cases you need acceleration when the car is not moving and the engine is moving near its idle, the only time you see full horsepower is when your car is at close to maximum speed in a gear lower than the most efficient gear for that speed.

OMG, if you REALLY want to get into a religious war, just go onto a car forum and start a fight over torque v. power. (As with most things, both sides have a valid point, and of course torque and power are intimately related, but power really is the more important stat.)

[mikegarrison]

What does matter is that SI units are based off of a unit of mass. Traditional English units were based off of a unit of force. That does make a difference.

Of course you can either use slugs or lb-m units for mass calculations with English units, but it does get confusing. People who use metric also tend to get confused, though. Most people think they weigh XXX in kg, but of course under SI units they actually weigh XXX*9.81 in Newtons. They *mass* XXX in kg, but for non-technical purposes most people don't care about the difference. So without realizing it they tend to use kg-f (which isn't a valid SI unit).

Just try Google. Type in "1 pound in kg" and see if it comes back saying "those units are incompatible". No, it comes back saying "0.453592".

[PB666]

Just now, mikegarrison said:

OMG, if you REALLY want to get into a religious war, just go onto a car forum and start a fight over torque v. power. (As with most things, both sides have a valid point, and of course torque and power are intimately related, but power really is the more important stat.)

Rated horsepower is meaningless, it is essentially the power you get from an engine just before you have done significant damage. If your car has a tachometer on it, and you floor the car, as soon as you go from green to orange, whatever horsepower that is, that hp is useless because you are scavenging the engines lifespan to get it. Another example, suppose Brazindia comes out with a brand new car and they quote you highway horsepower rating of say 400 horse power, ask to see the torque profile, if that car is going down the highway at 100 MPH but the engine is reving at 3500 to 4000 RPM, who in the devil would want to drive that car. So for example a previous car of mine was not rated for horsepower, its what you might call a sleeper, it produced 200 fp of torque from about 1500 RPM up to about 3000 RPM, it was 1700 RPM at 70 mph and at 105 mph (170 km/h dont ask) switch back into 3rd gear from overdrive (torque converter lock) at 2550 RPM. Nope, I only look at torque to weight ratios in the 1500 to 2500 range, anything higher is simply BS power.

[mikegarrison]

Just now, PB666 said:

Rated horsepower is meaningless, it is essentially the power you get from an engine just before you have done significant damage. If your car has a tachometer on it, and you floor the car, as soon as you go from green to orange, whatever horsepower that is, that hp is useless because you are scavenging the engines lifespan to get it. Another example, suppose Brazindia comes out with a brand new car and they quote you highway horsepower rating of say 400 horse power, ask to see the torque profile, if that car is going down the highway at 100 MPH but the engine is reving at 3500 to 4000 RPM, who in the devil would want to drive that car. So for example a previous car of mine was not rated for horsepower, its what you might call a sleeper, it produced 200 fp of torque from about 1500 RPM up to about 3000 RPM, it was 1700 RPM at 70 mph and at 105 mph (170 km/h dont ask) switch back into 3rd gear from overdrive (torque converter lock) at 2550 RPM. Nope, I only look at torque to weight ratios in the 1500 to 2500 range, anything higher is simply BS power.

See? Like I said, the religious wars begin.

What accelerates your car? It's force at the wheel, right? OK, so where does that force come from? It comes from the torque of the engine *as supplied at the current speed*. But torque*rpm (torque at any given speed) is ... power.

You are right that peak power can be misleading. What is important is average power in the band of interest. If you are winding out a sports car on a race track, then that band of interest is very near the peak, and peak power is very important. If you never in your life push the throttle pedal all the way to the floor, then of course the band that is more interesting to you is somewhere in the middle of the power curve.

And when you ask "who would want to drive that car" that is revving at 4000 rpm on the highway -- that would be me. I have a Honda S2000, and it tends to rev even higher than that just driving it around on city streets. And it's hella fun to drive. (Or at least it was, until I turned it into a track car. Now I often drive my Honda Element, and with that car I'm tooling around at more like 2500 rpm. Both types of designs work fine.)

[p1t1o]

Thinking about it, I think the stat I am most interested in when it comes to judging cars is time for 0-60mph (or 62mph/100kmh, since we are talking metric/Imperial) in seconds.

Power, torque, horsepower...time to speed gives a more practical picture, or so it seems to me anyway.

(I couldn't find a an Imperial unit for time)

 

[GoSlash27]

The #1 thing that keeps Metric from taking off in the US: American rules football.
If we switch from yards to meters, it screws up both the game and the records. It's a silly objection, but a very real one.

 I'm personally a big fan of metric, but my estimates are still rooted in imperial. And yeah... I'm on the "torque" side of the argument. "horsepower" is an indication of the peak power of an engine, but it only occurs at a single RPM and gives no indication of how widely dispersed it is across the operating RPM band.

Best,
-Slashy

[Darnok]

If we are talking about every day common use then metric seems fine.

But in science modified imperial system would be better, because universe doesn't work in 10-based numeric system.

[andrewas]

The universe doesn't work in any units system. Imperial or metric are both equally useful when it comes to describing observed phenomena. Imperial loses its advantages when working outside the human scale it was designed for. Metric offers easier arithmetic. It would be even better in base 12, but it's way to late to make that conversion now.

[YNM]

Cars... Hmm, I think what matters is where it's economy spot is. If you're going around in a congested city you don't need big cars or huge engines (higher torque could help making fast changes in a congestion). But when you're crossing the country you need something that can go sliightly fast and still economical (which means, more power).

Says the guy that have only japanese cars. Not many european / american cars here, even the american ones gave up.

Edit: Apart from cars, interesting point to bring up about base two or three being easier to use. Never get on that myself but probably should try it. Even while using metric having sense of half and a third is quite helpful, quite horrible for a third though.

 

Edited February 17, 2016 by YNM

[Tex_NL]

1 hour ago, Darnok said:

If we are talking about every day common use then metric seems fine.

But in science modified imperial system would be better, because universe doesn't work in 10-based numeric system.

It probably all comes down to what you've been thought as a child but what you're saying is exactly the opposite of what most believe. Imperial is has no logic. In science an technology metric is king.

And not switching to metric because of American Football as GoSlash is suggesting is complete bolocks of course. Nothing is preventing you from using an antiquated system in sports.

Edited February 17, 2016 by Tex_NL
Crappy censor tried to moderate my post. NOT gonna happen!

[Darnok]

43 minutes ago, andrewas said:

The universe doesn't work in any units system. Imperial or metric are both equally useful when it comes to describing observed phenomena. Imperial loses its advantages when working outside the human scale it was designed for. Metric offers easier arithmetic. It would be even better in base 12, but it's way to late to make that conversion now.

Universe works in math constants units system That is why I said "modified imperial" not exact imperial.
Key idea is to use different numeric system for different real/natural event or physical property of matter and energy. If you find correct numerical system you won't get meaningless numbers like @PB666 described in his post (1.616199(97) × 10⁻³⁵) instead you will have natural numbers like 1, 2 or 10 is π in π-nary system just like 10 is 2 in binary system.

[LN400]

18 hours ago, PB666 said:

Actually for physics the units should be:

• the gravitational constant, G,
• the reduced Planck constant, ħ,
• the speed of light in a vacuum, c,
• the Coulomb constant, 1/4πε₀ (sometimes k_e or k), and
• the Boltzmann constant, k_B (sometimes k).
• L = 1.616199(97) × 10⁻³⁵m
• M = 2.17651(13) × 10⁻⁸kgth
• T = 5.39106(32) × 10⁻⁴⁴s
  [Note the lack of precision in the above units is due to uncertainty in the universal gravitational constant]

I'm not getting into a debate over which system is "the best" but rather a slight correction to the quoted post.

The units for these constants are there following the SI (metric based) standard.

Constant [unit]

G [N*m²/kg]

ħ [J*s]

c [m/s]

k_e [N*m²/C²]

Not sure what the others are (L could be Avogadro's constant with the unit 1/mol but it doesn't seem to be the same L).

Edited February 17, 2016 by LN400
Fixing typo

[Tex_NL]

5 minutes ago, Darnok said:

Universe works in math constants units system That is why I said "modified imperial" not exact imperial.

Getting people to change from one system to another is difficult. Very difficult. But geting people to change to a system that is both very similar and at the same time very different is nearly impossible. That way you invite cock-ups. It won't be a matter of if things will go wrong but when.
If you are getting people to change get them to change to the most most logical and widest used system. It will take just as much effort and makes everybody's life (on both sides of the equation) a lot easier.