Posted by RamRod Sword of Baal on April 17, 2009, 6:27 pm
> wrote:
>>
>>> SI requires no 'conversion factors'. That's why it's simpler.
>>>
>>
>>Actually, it *does* use conversion factors, it's just that they all happen
>>to be 1-something (1J = 1 N-m, or 1W = 1 J/s)
>>
>>If you don't keep track of the units being used, it's just as easy to
>>screw
>>up something in the SI system as any other. Can't tell how many times
>>I've
>>caught students trying to say 1m + 1 N = 2J. Ever try to add units of
>>length with units of force? Keeping track of the units and using even SI
>>conversions is essential to doing the right calculations.
>>
>>Where did you Europeans ever get the idea to measure force using kilograms
>>anyway?
> We use Newtons, not kg
>>While the proper unit for pressure is the Pascal (or kPa or MPa),
>>why do you have pressure gauges that measure 'kg / cm^2'? What's up with
>>that?
> The Europeans might, the Brits (general public when inflating tyres)
> commonly use psi or occasionally bar ( = 100 kPa) Real world
> engineering uses psi, bar, Pa depending on which way the wind is
> blowing and the specific application.
> Many years ago I heard an Australian weather forecast that used Hecto
> Pascals this was the first time I had ever seen the hecto multiplier
> in use (with the exception of hectares!) after 20 years of using SI
> units and I vaguely recalled the first day I saw a list of SI
> multipliers. I knew the numbers (circa 1000) they quoted were in the
> same region as those for millibars, but until I sat down and really
> thought about it I was totally convinced that by using Hecto Pascals
> they were out by a factor of 10.
>>Not that I'm a big fan of the US imperial system, but there are a few
>>tricks
>>that work well. One lbm always exerts one lbf due to gravity. Heating up
>>one lbm of water one degree F takes just one BTU. Maybe a few others.
> Substitute 1 kg, 1 deg K, 1 Joule, 1 Newton as necessary
> It's ok I do know about metric water :)
It tastes much better than Imperial water :-)
Posted by Eeyore on April 17, 2009, 6:45 pm
Mike wrote:
> >> SI requires no 'conversion factors'. That's why it's simpler.
> >
> >Actually, it *does* use conversion factors, it's just that they all happen
> >to be 1-something (1J = 1 N-m, or 1W = 1 J/s)
> >
> >If you don't keep track of the units being used, it's just as easy to screw
> >up something in the SI system as any other. Can't tell how many times I've
> >caught students trying to say 1m + 1 N = 2J. Ever try to add units of
> >length with units of force? Keeping track of the units and using even SI
> >conversions is essential to doing the right calculations.
> >
> >Where did you Europeans ever get the idea to measure force using kilograms
> >anyway?
> We use Newtons, not kg
> >While the proper unit for pressure is the Pascal (or kPa or MPa),
> >why do you have pressure gauges that measure 'kg / cm^2'? What's up with
> >that?
> The Europeans might, the Brits (general public when inflating tyres)
> commonly use psi or occasionally bar ( = 100 kPa) Real world
> engineering uses psi, bar, Pa depending on which way the wind is
> blowing and the specific application.
> Many years ago I heard an Australian weather forecast that used Hecto
> Pascals this was the first time I had ever seen the hecto multiplier
> in use (with the exception of hectares!) after 20 years of using SI
> units and I vaguely recalled the first day I saw a list of SI
> multipliers. I knew the numbers (circa 1000) they quoted were in the
> same region as those for millibars, but until I sat down and really
> thought about it I was totally convinced that by using Hecto Pascals
> they were out by a factor of 10.
> >Not that I'm a big fan of the US imperial system, but there are a few tricks
> >that work well. One lbm always exerts one lbf due to gravity. Heating up
> >one lbm of water one degree F takes just one BTU. Maybe a few others.
> Substitute 1 kg, 1 deg K, 1 Joule, 1 Newton as necessary
4.2 Joules sadly ( 4.1813 to be exact ). Yes cgs used calories and it was one,
but SI physics sees no point in using water as a reference for specific heat.
http://en.wikipedia.org/wiki/Specific_heat_capacity
Graham
Posted by Scott on April 15, 2009, 12:14 am
On Tue, 14 Apr 2009 22:08:56 +0100, in alt.energy.homepower, Mike
>But he's right. BTU's went out with the ark, even those that still
>use feet and pounds in the UK no longer use BTU's.
I didn't say he wasn't right, I said he was a snob.
However, "out with the ark" suggests what we geeks call a "heat seeker"
mentality, a tendency to glom onto the new just because it's new, without
necessarily considering the merits of whatever it might be replacing.
Someone else said it: Just because it's old doesn't mean it's good, and just
because it's new doesn't mean it's better.
I wonder, do SI countries talk about gas cooktops in terms of watts?
Posted by Eeyore on April 15, 2009, 9:05 am
Scott wrote:
> >But he's right. BTU's went out with the ark, even those that still
> >use feet and pounds in the UK no longer use BTU's.
> I didn't say he wasn't right, I said he was a snob.
> However, "out with the ark" suggests what we geeks call a "heat seeker"
> mentality, a tendency to glom onto the new just because it's new, without
> necessarily considering the merits of whatever it might be replacing.
> Someone else said it: Just because it's old doesn't mean it's good, and just
> because it's new doesn't mean it's better.
> I wonder, do SI countries talk about gas cooktops in terms of watts?
Of course. Ditto microwave ovens. What do you use ?
Graham
Posted by harry on April 16, 2009, 7:08 pm
On Apr 15, 1:14 am, nob...@xmission.com (Scott) wrote:
> On Tue, 14 Apr 2009 22:08:56 +0100, in alt.energy.homepower, Mike
> >But he's right. BTU's went out with the ark, even those that still
> >use feet and pounds in the UK no longer use BTU's.
> I didn't say he wasn't right, I said he was a snob.
> However, "out with the ark" suggests what we geeks call a "heat seeker"
> mentality, a tendency to glom onto the new just because it's new, without
> necessarily considering the merits of whatever it might be replacing.
> Someone else said it: Just because it's old doesn't mean it's good, and just
> because it's new doesn't mean it's better.
> I wonder, do SI countries talk about gas cooktops in terms of watts?
Yep we do! And gas boilers.
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>>
>>> SI requires no 'conversion factors'. That's why it's simpler.
>>>
>>
>>Actually, it *does* use conversion factors, it's just that they all happen
>>to be 1-something (1J = 1 N-m, or 1W = 1 J/s)
>>
>>If you don't keep track of the units being used, it's just as easy to
>>screw
>>up something in the SI system as any other. Can't tell how many times
>>I've
>>caught students trying to say 1m + 1 N = 2J. Ever try to add units of
>>length with units of force? Keeping track of the units and using even SI
>>conversions is essential to doing the right calculations.
>>
>>Where did you Europeans ever get the idea to measure force using kilograms
>>anyway?
> We use Newtons, not kg
>>While the proper unit for pressure is the Pascal (or kPa or MPa),
>>why do you have pressure gauges that measure 'kg / cm^2'? What's up with
>>that?
> The Europeans might, the Brits (general public when inflating tyres)
> commonly use psi or occasionally bar ( = 100 kPa) Real world
> engineering uses psi, bar, Pa depending on which way the wind is
> blowing and the specific application.
> Many years ago I heard an Australian weather forecast that used Hecto
> Pascals this was the first time I had ever seen the hecto multiplier
> in use (with the exception of hectares!) after 20 years of using SI
> units and I vaguely recalled the first day I saw a list of SI
> multipliers. I knew the numbers (circa 1000) they quoted were in the
> same region as those for millibars, but until I sat down and really
> thought about it I was totally convinced that by using Hecto Pascals
> they were out by a factor of 10.
>>Not that I'm a big fan of the US imperial system, but there are a few
>>tricks
>>that work well. One lbm always exerts one lbf due to gravity. Heating up
>>one lbm of water one degree F takes just one BTU. Maybe a few others.
> Substitute 1 kg, 1 deg K, 1 Joule, 1 Newton as necessary
> It's ok I do know about metric water :)