How efficient is my car?

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Offline Geezer

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How efficient is my car?
« on: 23/08/2009 06:16:16 »
I get an an average of 30 MPG (US gallons) when my car travels 10,000 miles.

How efficient is my car?

My big honking, conspicuous consumption, Dodge truck only averages 20 MPG in 10,000 miles.

How inefficient is my truck?
There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.

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Offline Geezer

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« Reply #1 on: 23/08/2009 06:36:16 »
BTW, questions are allowed.
There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.

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Offline Chemistry4me

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« Reply #2 on: 23/08/2009 06:43:21 »
Can you convert that into kilometers/litres? [:)]

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Offline Geezer

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« Reply #3 on: 23/08/2009 06:58:09 »
Yes, but you'll have to wait till tomorrow because I'm going night-night now.

Hints:

1 US gal = 3.7854 liters (litres?)
1 anybody mile (except Scotland) = 1.609344 km
There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.

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Offline RD

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« Reply #4 on: 23/08/2009 07:14:16 »
1 anybody mile (except Scotland) = 1.609344 km

Quote
Scots mile

The Scots mile was longer than the English mile, but varied in length from place to place. It was formally abolished by an Act of the Parliament of Scotland in 1685, and again by the Treaty of Union with England in 1707, but continued in use as a customary unit during the 18th century. It was obsolete by the time of its final abolition by the Weights and Measures Act 1824.
http://en.wikipedia.org/wiki/Mile#Scots_mile
« Last Edit: 23/08/2009 07:17:13 by RD »

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Offline Geezer

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« Reply #5 on: 23/08/2009 07:26:00 »
Gordon Bennet!

The reference to Scotland was (supposed to be) entertaining.

Now, we all know who Gordon Bennet was, but who made him famous in the second half of the twentieth century?
There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.

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Offline RD

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« Reply #6 on: 23/08/2009 08:10:36 »
Now, we all know who Gordon Bennet was, but who made him famous in the second half of the twentieth century?

Alf, (not the cat-eating space-alien).
« Last Edit: 23/08/2009 08:13:04 by RD »

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Offline Geezer

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« Reply #7 on: 23/08/2009 16:11:50 »
I think you are right. Who played Alf?
There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.

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Offline Mcdaniels96

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How efficient is my car?
« Reply #8 on: 23/08/2009 16:31:53 »
great

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Offline Karsten

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« Reply #9 on: 23/08/2009 19:09:37 »
234.5 divided by miles per gallon (mpg) gives you liter/100km.

234.5 divided by liter/100km gives you mpg.

Pretty close at least. Can't remember how I got that number (234.5) but I did the conversion once and the number is all I remember. Good enough.
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Offline Geezer

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« Reply #10 on: 23/08/2009 20:02:37 »
Looks about right. I get 235.21

For MPG to km/l, multiply by 1.609344 and divide by 3.7854 = 0.4254145

For km/l to l/km, 1 divided by .4254145 = 2.3521386

For l/km to l/100km, multiply by 100 = 235.21

Now we have all the unit conversions out of the way, how efficient IS my car, or anybody's car come to that?  [:D]
There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.

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Offline Nizzle

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« Reply #11 on: 24/08/2009 10:32:43 »
You guys do know that google is a converter as well right?

If you type "20mpg to L/100Km" you'll get the answer from google (20 miles per gallon = 11.7607292 l/100km)
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Offline Geezer

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« Reply #12 on: 24/08/2009 16:58:56 »
...and Google get's it right too. Looks like there is something horribly wrong with my calculation!
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Offline Geezer

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« Reply #13 on: 24/08/2009 17:05:41 »
I take it back. It's OK. (I was multiplying 235 by the MPG! )
There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.

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Offline JimBob

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« Reply #14 on: 25/08/2009 03:59:29 »
Are you THAT old?

And what happened to the efficiency question. Lets look at it another way.

How many calories are in a gallon (or litre for you Europeans) and how many calories do the engines of each vehicle produce? By dividing calories produced by total calories you get efficiency. 

So, Geezer, how many calories per mile do you use?

 
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Offline Geezer

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« Reply #15 on: 25/08/2009 04:30:52 »
Nope. That might tell me how efficient the engine in my car is. I want to know how efficient my car is.
There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.

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Offline RD

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« Reply #16 on: 25/08/2009 04:33:23 »
Quote
... most engines retain an average efficiency of about 18%-20%
http://en.wikipedia.org/wiki/Internal_combustion_engine#Energy_efficiency

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Offline Geezer

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« Reply #17 on: 25/08/2009 04:38:19 »
Nope. Not the engine, the car.
There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.

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Offline RD

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« Reply #18 on: 25/08/2009 04:45:26 »
I want to know how efficient my car is.
At best as efficient as the engine.

(vehicle aerodynamics and your driving style can reduce efficiency).

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Offline Geezer

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« Reply #19 on: 25/08/2009 04:54:21 »
Well, OK. But let's ask another related question.

Is my car more efficient than my truck?
There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.

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Offline RD

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« Reply #20 on: 25/08/2009 05:02:17 »
The efficiency of car and truck engines will be about the same.

If the car is more aerodynamic (lower drag) than the truck then it will be more efficient than the truck. 

The higher rolling resistance of the truck's bigger tyres would also lower its efficiency compared with the car,
 (which probably has smaller & smoother tyres than the truck).
« Last Edit: 25/08/2009 05:11:04 by RD »

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Offline Geezer

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« Reply #21 on: 25/08/2009 06:21:11 »
There you go with that engine thing again. Now, imagine I have to haul 1500 pounds of gravel for a hundred miles. Would my car be more efficient than my truck?
There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.

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Offline Mazurka

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« Reply #22 on: 25/08/2009 08:24:25 »
I don't think that it is reasonable to try and quantify how eficient two different vehicles, without setting out some baseline circumstances to work from.   

It is reasonable to give comparative statements - the truck is more efficient at hauling stone than the car.  The car is more efficient at moving people around safely (or whatever).

It strikes me that this is more a question of utillity than one of figures? 

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Offline RD

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« Reply #23 on: 25/08/2009 08:44:28 »
Efficiency: the percentage of the chemical energy in the fuel which is converted into kinetic energy.

kinetic energy = 1/2 x (mass of vehicle & load) x (speed of the vehicle)2 .

Strap a refrigerator to the roof of your car and the increased air resistance would reduce its MPG to that of your truck.
« Last Edit: 25/08/2009 08:59:08 by RD »

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lyner

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« Reply #24 on: 25/08/2009 10:36:50 »
Efficiency: the percentage of the chemical energy in the fuel which is converted into kinetic energy.

kinetic energy = 1/2 x (mass of vehicle & load) x (speed of the vehicle)2 .

Strap a refrigerator to the roof of your car and the increased air resistance would reduce its MPG to that of your truck.
The accepted definition includes "useful work", not just KE. After all, going at 70mph, mile after mile, involves no increase in KE but involves steady expenditure of work.

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Offline RD

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« Reply #25 on: 25/08/2009 11:46:34 »
Efficiency: the percentage of the chemical energy in the fuel which is converted into kinetic energy.

kinetic energy = 1/2 x (mass of vehicle & load) x (speed of the vehicle)2 .

Strap a refrigerator to the roof of your car and the increased air resistance would reduce its MPG to that of your truck.
The accepted definition includes "useful work", not just KE. After all, going at 70mph, mile after mile, involves no increase in KE but involves steady expenditure of work.

expenditure of work primarily against air resistance (when travelling at a constant speed).

By stating KE = 1/2 m v 2  I was trying to point out that more energy would be would be required to attain the same speed with additional mass (gravel), but the efficiency of the engine would be the same.  Loading the vehicle does not make it less efficient but does mean that more energy is required to attain the same speed as when unloaded.

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Offline Geezer

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« Reply #26 on: 25/08/2009 17:53:32 »
OK, I admit it. It was a loaded question!  [;D]

Without asking a lot of questions like "efficient at doing exactly what, big guy?", it's not possible to answer the question - although I did leave a clue about asking questions.

The measure of "efficiency" might not even have anything to do with fuel consumption (a red herring, I confess). For example, we might only be interested in the efficient use of the driver's time. Clearly the truck is much more efficient in that respect if we have to lug 1500 pounds of gravel somewhere.

There ain'ta no sanity clause, and there ain'ta no centrifugal force Šther.