Pound v. Foot Pound

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Re: Pound v. Foot Pound

Postby gmalivuk » Fri Sep 06, 2013 7:50 pm UTC

idobox wrote:
gmalivuk wrote:What you are claiming is patently false, idobox. I have definitely talked to people who don't remember all the metric prefixes or how to convert between them. Not everyone pays for their own water, so many likely don't know that there are 1000L in a m^3. And as I said, they have no excuse but stupidity. Americans can at least excuse their ignorance by not being able to quickly multiply things by the 231 cubic inches in a gallon, for example.

Also, there are 35840 ounces in an imperial ton, and 63,360,000 mils in a mile. The first one required some mental math, and the second one I already knew. I'm probably not the right person to challenge with odd USCS units when you're trying to make a point about its confusingness.
But people who don't know the micro-milli-kilo-mega? I've lived most of my life in France, and I have yet to met somebody who gets confused by it. I've even used k€ and M€ at my work.
It turns out people can be confused about things and not tell you. Also, I suspect that you have met some people without having a conversation that required them to figure out that there are 100,000cm in a km or 1,000,000mL in a cubic meter or whatever.

And you seriously memorize numbers like 63,360 ? why?
For one thing, it helps when idiots such as yourself toss out a "challenge" question to try to "prove" how inferior the USCS is.

Do you remember any old phone numbers or addresses or friends' old phone numbers or addresses or the price of your regular lunch at your regular lunch cafe or whatever? I don't need to "memorize" a five-digit number in order to remember it. Do you remember how to get places in your town? Even places you don't go often? That requires a lot more "memorization" than 5 digits and yet you do it automatically, even though you could just check Google every time you need to go there.

Knowing there are 1609.344 meters in a mile required a few seconds of conscious effort to memorize, as did 43,560 square feet in an acre, but I really don't think 63,360 inches in a mile did.

But in any case, do you really mean to tell me you've never memorized more than two or three digits of a number like pi or e or sqrt(2) or the golden ratio, even though you'd never do math that needed more precision than that without also being able to just tell a computer or calculator to spit out the extra digits?

That's what I was taught in primary school. Liters are not a scientific unit, and should be used only for quantities of fluids.
Calories aren't an SI unit, either. Nor are minutes, hours, days, months, or years. Nor are light years or parsecs or kilowatt-hours or atmospheres or degrees Celsius. And yet, I'm pretty sure you've used most or all of those at one time or another in a scientific setting, without ever worrying about the non-SI nature of your units. (Incidentally, liters *are* metric units, as are hectares. Metric is not the same as SI, and I'm tempted to conclude that the confusion between the two is just another example of the lazy, fuzzy-headed reasoning people start to slip into when the only math they ever have to do is slide a decimal point one way or the other.)

You can still use cc to measure fluids, but people tend to be confused by the cube law and think there are 10 cc in a cubic decimeter
I thought you said people weren't confused by unit conversions with the metric system?
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Re: Pound v. Foot Pound

Postby slinches » Fri Sep 06, 2013 8:36 pm UTC

This whole discussion seems to have gone a bit sideways. Units are a way of expressing some physical quantity in a useful way. And the reason there are so many different ones is that they are useful when used in a context where they make sense (usually in the field they were created for, sometimes elsewhere as well). It would be ridiculous to quote engine power in eV/s, but that doesn't mean the eV is bad unit. It just means that it's not well suited for that purpose.

The key for making calculations easy is to choose to measure in the best units for that task. For cooking that may mean using oz and cups, but that system probably isn't the best option if you're trying to make thermodynamics calculations. Consistent unit systems (Warning: link to pdf) are a reasonable compromise in this regard, but each system will have some units that are difficult to grasp. I use the in-lbf-s consistent unit system on a daily basis so I know my mass is 0.46 slinches, but I really don't understand how that relates to my daily experiences unless I convert it to lbm or kg.

Ultimately, it really doesn't matter what units you use as long as you're comfortable with them. Just quote the results in ones that make sense for the audience. And if that audience is the general public, just make something up. They won't know better anyway.

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Re: Pound v. Foot Pound

Postby davidstarlingm » Fri Sep 06, 2013 8:40 pm UTC

idobox wrote:
davidstarlingm wrote:
idobox wrote:...cc and ml are not exactly the same, the first measures a volume, and as much as I know is mostly used for motors, the other measure a quantity of fluid, and is massively used in everyday's life.

Uhm, ml measures a volume as well. Or the quantity of fluid which fits within that volume, but same difference. In my experience, recommended fluid dosages are given in ccs as often as they are given in ml. They really are exactly the same.

That's what I was taught in primary school. Liters are not a scientific unit, and should be used only for quantities of fluids. You can still use cc to measure fluids, but people tend to be confused by the cube law and think there are 10 cc in a cubic decimeter, so liters are usually preferred. Anyway, that's only a minor point, and it might only be relevant in my own country.

What country are you in? I honestly can't remember hearing cc used for fluids anywhere other than American medical shows.

I have used (and commonly see other people using) liters to describe quantities of water, blood, gasoline, air, sand, pebbles, and a variety of other substances. Granted, all of those are "fluids" in the sense that they can flow or be poured, but my point is that it's a common metric unit of volume. It's not the SI unit of volume, but that doesn't necessarily make it less scientific any more than lightyears are unscientific because they aren't meters. Why would it be more scientific to use them for quantities of fluids?

I'm in the States, and syringes are sometimes marked in ccs and sometimes in mL, usually alongside fluid ounces as well.

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Re: Pound v. Foot Pound

Postby Copper Bezel » Fri Sep 06, 2013 9:28 pm UTC

gmalivuk wrote:What you are claiming is patently false, idobox. I have definitely talked to people who don't remember all the metric prefixes or how to convert between them. Not everyone pays for their own water, so many likely don't know that there are 1000L in a m^3. And as I said, they have no excuse but stupidity. Americans can at least excuse their ignorance by not being able to quickly multiply things by the 231 cubic inches in a gallon, for example.

Also, there are 35840 ounces in an imperial ton, and 63,360,000 mils in a mile. The first one required some mental math, and the second one I already knew. I'm probably not the right person to challenge with odd USCS units when you're trying to make a point about its confusingness.


I want to get into the unit argument, but actually, I'm just overjoyed to encounter a non-nonsense term for the US unit system. That's a wonderful thing.
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Re: Pound v. Foot Pound

Postby gmalivuk » Fri Sep 06, 2013 10:29 pm UTC

Often people call it the Imperial system, but that's incorrect because for example an imperial ton is 2240lbs while a US ton is 2000, and liquid volumes don't match either.

And to be clear, of course the USCS is rather strange and full of interestingly archaic and impractical unit conversions. I personally use metric (or geometric units where G=c=1) whenever I'm doing scientific math or communicating with non-Americans, because it's more widespread and less cumbersome to do conversions with.

What I take issue with are people like idobox who argue so badly for a position that really should be easier to support. I mean, excuse people's ignorance of something as simple and widely used as the hectare, and then demand that I do conversions with grains and imperial tons? Both of which are far less commonly used than the hectare? And then scoff at the fact that I memorized 63,360 while users of the superior metric system haven't memorized 10,000? All after literally claiming that having trouble with the metric system can't happen?

I am disappoint.
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Re: Pound v. Foot Pound

Postby idobox » Fri Sep 06, 2013 10:46 pm UTC

gmalivuk wrote:For one thing, it helps when idiots such as yourself toss out a "challenge" question to try to "prove" how inferior the USCS is.

Do you remember any old phone numbers or addresses or friends' old phone numbers or addresses or the price of your regular lunch at your regular lunch cafe or whatever? I don't need to "memorize" a five-digit number in order to remember it. Do you remember how to get places in your town? Even places you don't go often? That requires a lot more "memorization" than 5 digits and yet you do it automatically, even though you could just check Google every time you need to go there.

Knowing there are 1609.344 meters in a mile required a few seconds of conscious effort to memorize, as did 43,560 square feet in an acre, but I really don't think 63,360 inches in a mile did.

But in any case, do you really mean to tell me you've never memorized more than two or three digits of a number like pi or e or sqrt(2) or the golden ratio, even though you'd never do math that needed more precision than that without also being able to just tell a computer or calculator to spit out the extra digits?

I tend to remember values up to the 2nd or 3rd significant figure because I'm simply unable to do math by head with more figure. That includes pi, e and sqrt(2).
I think I used to know pi to 4 or 5 digits, but I don't trust my memory on this.
And I was genuinely surprised that anybody would remember that kind of number.

I seem to have annoyed you or something. The metric system isn't perfect, with the story between g and kg for example, and yes, people get confused with cubes of units.
Calories for example are still found on food packaging (although accompanied by kJ), and we sometimes hear numbers given in light years, hours or kWh for sure, but the first thing we do when trying to do any form of science is to convert that to SI, or at least metric.

Now, the metric system was designed by scientists to be easy to use, and it is vastly superior to the imperial system in that regard. Yes, there is a lot of inertia when changing system, and even today in France we use non metric units. The imperial system is a legacy from pre-industrial England, and has been abandoned by pretty much everybody because it is archaic.

Then, I do slightly more math in my everyday life than move a decimal point.
And I certainly don't appreciate the Ad Hominem attack, especially from a moderator. If you need to remember complex conversion factors to defend your precious system against idiots like me, I think that tells a lot about you. I honestly don't care if the US want to keep their system, the same as I don't care which side of the road people drive, I'm not offended by people claiming that a factor 12 is superior to a factor 10, even though I think they're wrong. I come on this forum to have smart discussions with smart people, and I happen to believe to the imperial system is more complex to use, to the point people were not able to give me their weight in one of their most used unit. I also believe the metric system is superior in that regard.
You can disagree with my arguments, you can attack them, you can show how stupid or mistaken they are, and that's fine with me, I'm here for that. You can also point it out when I start to act like a troll, I'm pretty stubborn and can get carried away.
But calling me an idiot because I claim 63,360,000 mils in a mile is not an easy number to remember or use is not acceptable.
Insinuating I'm a stupid air-headed moron who can't do math because I used metric instead of SI, when metric became SI in 1960 is not acceptable either

What I take issue with are people like idobox who argue so badly for a position that really should be easier to support. I mean, excuse people's ignorance of something as simple and widely used as the hectare, and then demand that I do conversions with grains and imperial tons? Both of which are far less commonly used than the hectare? And then scoff at the fact that I memorized 63,360 while users of the superior metric system haven't memorized 10,000? All after literally claiming that having trouble with the metric system can't happen?

We have people who can't convert an hectare because they don't know how much an hectare represents, they have no idea if it's about 10 or 1000 000m².
You have people who can't convert between two units they often use.

My claim was stronger than what I could defend, that's still not an excuse to call me an idiot.
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Re: Pound v. Foot Pound

Postby gmalivuk » Fri Sep 06, 2013 10:55 pm UTC

I don't "need to remember" conversion factors for arguments, I just happen to remember them because 5-digit numbers aren't actually hard to remember., and this turns out to *also* be super convenient for arguments where you hope to trip me up by asking for a conversion involving a unit far less commonly used than the simple straightforward hectare.
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Re: Pound v. Foot Pound

Postby eSOANEM » Fri Sep 06, 2013 11:40 pm UTC

idobox wrote:I'm in the UK right now, and most of the people I know here are scientists, so I can't make a meaningful poll, but I feel confident almost everybody knows there are 1000L in a cubic meter.


Nah, as a physics student in the UK, I can definitely say lots of people do not know this. The reason is that in school when you're taught units in primary school or so, volume is always in litres (or usually millilitres) rather than m3 (or cm3).

Then you start doing maths and calculating volumes in m3 (or cm3) and now you have two separate units for volume and you probably have not been taught any connection.

It's not until you do chemistry and the teacher starts slipping between millilitres and cm3 that you get taught the connection.
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Re: Pound v. Foot Pound

Postby yurell » Sat Sep 07, 2013 11:00 am UTC

I always work backwards from 1L of water is roughly 1kg, 1m3 of water is roughly 1 tonne.
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Re: Pound v. Foot Pound

Postby Red Hal » Sun Sep 08, 2013 8:06 am UTC

That's where my brain makes the connection too. I remember that 1m3 is a thousand litres is a tonne of water is 1/pi metric fucktonnes. But I straddle the line (not between discord and rhyme but temporally) between the Imperial and Metric systems. I have vague memories from my youth of shillings and being given a sixpence (not relevant but background context) I still estimate the dimensions of animals (humans included) in feet and inches, hands and stone, and find the American system slightly confusing.

One of the advantages of the Imperial system from an everyday perspective is that it has a tendency to come up with integer numbers when measuring everday quantities. People are five feet. Six is tall, four is short, seven is very tall, three is very short. Convert this to metres and that simple relationship between integers and adjectives is lost. The same with weight. Ten stone is a good starting point for a human; double the height in feet.
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Re: Pound v. Foot Pound

Postby Derek » Tue Sep 10, 2013 7:25 am UTC

Red Hal wrote:People are five feet. Six is tall, four is short, seven is very tall, three is very short.

Uhh, five feet is pretty damn short, even for women. At least among western nations.

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Re: Pound v. Foot Pound

Postby meat.paste » Tue Sep 10, 2013 3:21 pm UTC

I can see why this thread is full of comment. I want to play :)

First off, I do think this is a lot of squawk over the name of something. A rose by any other name, yes? Units are used for consistency, but inter-conversion is always practical.

sin(x) is the same whether you use x as degrees or use x*2*pi/360 radians. Usually in math, angles are in radians. In my experience, angles in the physical world are measured in degrees. The sin function is the same.

If I have any function f(x) that has no discontinuities and all the other usual crap you have to say to make it a well behaved function, then I can always translate f(c*x) back into f(x) by multiplying by a constant (many times out side the function, but sometimes it has to be within the function [I'm looking at you trig functions]).

A hectare is a metric unit. An are is 100 m^2 A hectare is 100 ares. It is not an MKS unit.

The second is a metric unit (part of the MKS and cgs systems) to the extent that all unified measurement systems need time (for now at least), and the metric system uses the same second that the imperial and US systems use (does any system use a different second?) Wikipedia has an interesting article about how the definition of the second has evolved over time.

Tempering chocolate occurs between 91-93 F. It has to do with the crystalline phase of the cocoa butter and that crystallization has a fairly sharp temperature range. Egg proteins are very sensitive to the temperature. At 40C, the egg yolk is like play-doh. At 42C, it's a solid. A steak at 135F is medium rare. At 150, it's shoe leather. There are many examples in cooking where a temperature difference of 20-25 F makes a HUGE difference.

A foot-pound can be interpreted as a unit of energy, just like the Nm can be.

A foot-pound and Nm can also be units of torque. Torque is a measure of force and has nothing to do with movement. If I take a wrench to a locked up bolt and apply torque, the potential energy of the system is increasing, the force is increasing on the bolt head and no work is occurring because there is no movement. As soon the wrench deforms the corners of the bolt, work has been done, the wrench flies off the bolt, my hand hits a sharp metal edge and begins bleeding profusely, I curse profoundly, and I swear to never to work on a fricking engine ever again.
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Re: Pound v. Foot Pound

Postby gmalivuk » Tue Sep 10, 2013 5:06 pm UTC

No, sine of radians and sine of degrees are not the same sine functions, because they don't take the same inputs to the same outputs and the derivative of one gives you a velocity (or a velocity component) while the other gives you some other quantity entirely.
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Re: Pound v. Foot Pound

Postby meat.paste » Thu Sep 12, 2013 11:28 pm UTC

gmalivuk wrote:No, sine of radians and sine of degrees are not the same sine functions, because they don't take the same inputs to the same outputs and the derivative of one gives you a velocity (or a velocity component) while the other gives you some other quantity entirely.


I'm not seeing the difference. I do all the derivations and then just handle the unit conversions when I want a numerical answer. Under this approach, would multiplying inches together to get square inches be a different multiplying function than multiplying meters together? It seems that I can create my own unit of angle measurement (the dizzy unit?) and the sine of a dizzy unit has a defined numerical answer just like the sine of the equivalent angle in degrees or radians. e^(i*pi)=-1 is certainly uglier if I measure in degrees, but it's still true, isn't it?
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Re: Pound v. Foot Pound

Postby gmalivuk » Thu Sep 12, 2013 11:53 pm UTC

meat.paste wrote:
gmalivuk wrote:No, sine of radians and sine of degrees are not the same sine functions, because they don't take the same inputs to the same outputs and the derivative of one gives you a velocity (or a velocity component) while the other gives you some other quantity entirely.


I'm not seeing the difference. I do all the derivations and then just handle the unit conversions when I want a numerical answer. Under this approach, would multiplying inches together to get square inches be a different multiplying function than multiplying meters together? It seems that I can create my own unit of angle measurement (the dizzy unit?) and the sine of a dizzy unit has a defined numerical answer just like the sine of the equivalent angle in degrees or radians. e^(i*pi)=-1 is certainly uglier if I measure in degrees, but it's still true, isn't it?
No, it isn't. It is a unitless, dimensionless equation. It gives you a numerical answer right off the bat. Adding in unit conversions means you're not evaluating the same function.

Inches times inches gives you square inches, and meters times meters gives you square meters. And those are both fine because they're both measures of area. But what, for example, does e^meter measure? To my mind, e^meter makes no sense, and yet that's what you get when you put units or dimensions into the wrong kind of function.

Suppose the angle at time t is t degrees. Then the vertical position is sin(t degrees) meters if it's going around a circle with 1m radius. And then the vertical velocity is... what? The derivative of sin(t) is supposed to be cos(t), but the vertical velocity at time t of our rotating thing is pi/180 cos(t degrees) meters per second. How is this the same function? How is it analogous to using different units for "dimensionful" things like length?

The only way that derivative works without admitting that you're using a different sine function is if you simply define "degree" as the scalar constant pi/180, in which case you still don't have a situation analogous to meters and inches, since neither the meter nor the inch is a scalar quantity.
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Re: Pound v. Foot Pound

Postby Tass » Fri Sep 13, 2013 5:48 am UTC

Well a degree simply has the value pi/180.

You could also do e^Mega just fine.

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Re: Pound v. Foot Pound

Postby eSOANEM » Fri Sep 13, 2013 8:53 am UTC

gmalivuk wrote:
meat.paste wrote:
gmalivuk wrote:No, sine of radians and sine of degrees are not the same sine functions, because they don't take the same inputs to the same outputs and the derivative of one gives you a velocity (or a velocity component) while the other gives you some other quantity entirely.


I'm not seeing the difference. I do all the derivations and then just handle the unit conversions when I want a numerical answer. Under this approach, would multiplying inches together to get square inches be a different multiplying function than multiplying meters together? It seems that I can create my own unit of angle measurement (the dizzy unit?) and the sine of a dizzy unit has a defined numerical answer just like the sine of the equivalent angle in degrees or radians. e^(i*pi)=-1 is certainly uglier if I measure in degrees, but it's still true, isn't it?
No, it isn't. It is a unitless, dimensionless equation. It gives you a numerical answer right off the bat. Adding in unit conversions means you're not evaluating the same function.

Inches times inches gives you square inches, and meters times meters gives you square meters. And those are both fine because they're both measures of area. But what, for example, does e^meter measure? To my mind, e^meter makes no sense, and yet that's what you get when you put units or dimensions into the wrong kind of function.


e^metre necessarily has no meaning. Take the power series of e^x, looks like there are multiple powers of x there each multiplied by dimensionless coefficients which are all summed together. Dimensionally, this can only be consistent if x is dimensionless.

Tass wrote:Well a degree simply has the value pi/180.

You could also do e^Mega just fine.


Whilst this does make the system consistent it is not particularly helpful and is not how degrees are taught. When I was taught radians at school, we were not told "by the way, a degree is just pi/180 so when you've done sin(90 degrees) you've been doing exactly the same as sin(pi/2)", we were told "when you're differentiating sin(x) you have to use radians otherwise you get wrong answers because they're different functions".

It's also problematic because, if I have a wave oscillating at 1Hz, I can now (under this definition of °) say, perfectly reasonably that ω=360°Hz? Can I divide by °? Does a wave with ω=360s-1 have a frequency of 1/° Hz?

It does make the system consistent but it also makes it clunky and bizarre. It is far more streamlined to acknowledge that the same distinction between frequency and angular frequency applies to angles 'in different units' and they should be treated as different quantities.
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Re: Pound v. Foot Pound

Postby elliptic » Fri Sep 13, 2013 2:51 pm UTC

gmalivuk wrote:No, sine of radians and sine of degrees are not the same sine functions.

And in other news, loge and log10 are not the same log functions.

But they are both log functions, and when I see a bare log() my head doesn't asplode: I just have to deduce what the base is supposed to be. In a mathematical context it's a safe bet that it's e by convention, but that's not always the case (eg my 12-year old nephew's homework, or the log button on my calculator).

Similiarly, sinrad(pi) = sindeg(180) = 0, and when I see a bare sin() I deduce which one it's supposed to be from the context.

Of course the special thing about radians is that differentiating sinanything else introduces an irritating constant factor that doesn't arise with sinrad. Radians are the "natural" scale for angles just as e is the "natural" base for logs. But that doesn't make other measures wrong, just less convenient.

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Re: Pound v. Foot Pound

Postby eSOANEM » Fri Sep 13, 2013 4:08 pm UTC

Yeah, no-one's saying they're unrelated functions, just that they are different functions. You can't arbitrarily switch between degrees and radians as you can any other pair of units for measuring the same quantity. This is the fundamental difference and this is why the only sensible interpretation is that they are distinct quantities.
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Re: Pound v. Foot Pound

Postby LaserGuy » Fri Sep 13, 2013 4:16 pm UTC

elliptic wrote:Of course the special thing about radians is that differentiating sinanything else introduces an irritating constant factor that doesn't arise with sinrad. Radians are the "natural" scale for angles just as e is the "natural" base for logs. But that doesn't make other measures wrong, just less convenient.


Related, but also: the small angle approximation also only really makes sense if you use radians. It still technically works, but the condition for "small" is strange and unintuitive in degrees.

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Re: Pound v. Foot Pound

Postby gmalivuk » Fri Sep 13, 2013 4:33 pm UTC

elliptic wrote:
gmalivuk wrote:No, sine of radians and sine of degrees are not the same sine functions.
And in other news, loge and log10 are not the same log functions.

Exactly. I'm glad you understand the point I've been making.

I wasn't arguing that sin(x degrees) isn't a sine function, but only that it's not the same function as sin(x radians).
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Re: Pound v. Foot Pound

Postby eSOANEM » Fri Sep 13, 2013 6:12 pm UTC

LaserGuy wrote:
elliptic wrote:Of course the special thing about radians is that differentiating sinanything else introduces an irritating constant factor that doesn't arise with sinrad. Radians are the "natural" scale for angles just as e is the "natural" base for logs. But that doesn't make other measures wrong, just less convenient.


Related, but also: the small angle approximation also only really makes sense if you use radians. It still technically works, but the condition for "small" is strange and unintuitive in degrees.


Also, sin(x)=pi/180 x for small x just doesn't have the same ring to it.
my pronouns are they

Magnanimous wrote:(fuck the macrons)


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