Steve, you seemed to have missed my point. If we describe fuel consumption
in L/km and convert to pure SI (ie convert everything in metres if possible
as is taught at A Level), we would set
1 L = 10^-3 m^3 and
1 km = 10^3 m
to get
1 L/km = 10^-6 m^2 1 L/km = 1 mm^2.
If on the other hand we converted km/l in the same way, we would get
1 km/L = 10^6 m^-2.
The question that was **implicitly** asked was, which is the more
meaningful way to describe petrol consumption: m^2 or m^-2. I was showing
how the use m^2 could be visualised. Obviously, if you accelerated hard,
then my string of petrol would get thicker.
PS I am a part-time A Level physics tutor.
_____
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf
Of Stephen Humphreys
Sent: 30 January 2008 10:14
To: U.S. Metric Association
Subject: [USMA:40309] Re: convenient numerical values
Martin, you keep forgetting how variable driving a car is (like the 0-60
discussion).
Acceleration, braking and parking on the M25 (joke - it's the worlds busiest
motorway) all have effects on consumption. Obv this affects mpg also.
_____
From: [EMAIL PROTECTED]
To: [email protected]
Subject: [USMA:40299] Re: convenient numerical values
Date: Tue, 29 Jan 2008 19:48:58 +0000
Bill,
I would prefer L/100 km, which, if converted to SI would be m². This would
be dead easy to visualize. Assume that fuel consumption is 10^-6 m². This
works out at (1 mm)². Now imagine a string of fuel snaking along the road
that you are using, square in cross-section with each side of the square
being 1 mm. Now imagine that you are driving along that road. As you drive
along the road, the string of fuel will be fed into your engine and will
propel your car.
I have not worked out what the cross-section would really be, I merely used
10^-6 m² as an example.
_____
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf
Of Bill Potts
Sent: 28 January 2008 06:20
To: U.S. Metric Association
Subject: [USMA:40255] Re: convenient numerical values
J. Ward wrote: 'As a physicist I would speak in terms of "per meter
squared."'
Maybe so (and we had a discussion on this list a few years ago, involving
that same ultimate reduction), but it is something that neither the
physicist nor the layperson can readily visualize (although the physicist
can rationalize its use).
_____
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