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Fuel consumption


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#1 harey

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Posted 12 October 2013 - 07:48 PM

In Europe, we measure the fuel consumption in litres per 100 km. It is quite convenient because I can easily figure out what a litre is (a little bit less than one and half standard wine bottle) and it is not hard to figure out a distance of 100 km. However, any teacher of physics would point out that volume should be measured in [m3] and distance in [m]. After simplification, I get that fuel consumption should be measured in [m2]. What does it represent?

 

In the U.S., the consumption is measured in miles/gallon. Quite convenient, too, just that in the MKSA system, I get [1/m2]. How do you represent that?


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#2 bonanova

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Posted 12 October 2013 - 07:58 PM

Spoiler for Looks like


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#3 harey

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Posted 12 October 2013 - 08:04 PM

Though correct, a little wordy. Can you imagine a physical object fitting this definition?


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#4 bonanova

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Posted 12 October 2013 - 08:15 PM

Sure. Rectangular Parallelepiped


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The greatest challenge to any thinker is stating the problem in a way that will allow a solution.
- Bertrand Russell

#5 harey

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Posted 12 October 2013 - 08:25 PM

"Rectangular Parallelepiped"s are usually not used to transport fuel.


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#6 dgreening

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Posted 13 October 2013 - 07:22 PM

when I first started mulling this over, I realized that miles/ gal or km/ liter are skipping several steps.

 

We really mean that gal of gas is sufficient to propel this vehicle so many miles.

 

I took a typical value for a US car [25 mpg] and started converting it. 

 

Values are approx

 

25 miles ~ 32 km

1 Gal ~ 3.7 Liters ~ 3.7/1000 Meters 3

 

25 Mile/ gal = 32 km/ 0.0037  meters 3 ~ 32,000/ 0.0037  /meters 2

 

therefore 25 miles/ gal ~ 118,400,000  /meter 2

 

I am at a loss for how this related to the parallel piped, though I cannot find anything else that makes sense.


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#7 superprismatic

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Posted 14 October 2013 - 12:43 AM



when I first started mulling this over, I realized that miles/ gal or km/ liter are skipping several steps.

 

We really mean that gal of gas is sufficient to propel this vehicle so many miles.

 

I took a typical value for a US car [25 mpg] and started converting it. 

 

Values are approx

 

25 miles ~ 32 km

1 Gal ~ 3.7 Liters ~ 3.7/1000 Meters 3

 

25 Mile/ gal = 32 km/ 0.0037  meters 3 ~ 32,000/ 0.0037  /meters 2

 

therefore 25 miles/ gal ~ 118,400,000  /meter 2

 

I am at a loss for how this related to the parallel piped, though I cannot find anything else that makes sense.

Well, I think that you have to add units to the numerator (as well as the denominator) to make any sense of things.

in your example, 25 miles/gal = 118,400,000/m2=118,400,000 parsecs/parsecs-m2.  Now that makes physical sense!


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#8 dgreening

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Posted 14 October 2013 - 05:18 AM

not sure what to make of

 

"Well, I think that you have to add units to the numerator (as well as the denominator) to make any sense of things.

in your example, 25 miles/gal = 118,400,000/m2=118,400,000 parsecs/parsecs-m2.  Now that makes physical sense!"


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#9 superprismatic

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Posted 14 October 2013 - 02:49 PM



not sure what to make of

 

"Well, I think that you have to add units to the numerator (as well as the denominator) to make any sense of things.

in your example, 25 miles/gal = 118,400,000/m2=118,400,000 parsecs/parsecs-m2.  Now that makes physical sense!"

What I was getting at is that 118,400,000 is missing an interpretation in units (in this case, units of length).  Any unit of length (including parsecs) would work.

So, for example, we could write 118,400,000 m/m3, where the units in the denominator refer to fuel.  But writing 118,400,000/m2 doesn't even hint

that the numerator should represent distance and the denominator should represent fuel volume.  I'll grant you that parsec-m2 is a rather strange unit of volume. 


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#10 harey

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Posted 16 October 2013 - 10:11 AM

Spoiler for Looks like

 

You got the first part to 97% - I wanted to hear "section of a pipeline along the trajectory". The tank of the U.S. scenario corresponds quite well to the pipeline, just the section of a tank is not measured in 1/m2, so the second part of the problem is still open.


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