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1.  

   

   Anonymous Coward, Apr 6th, 2011 @ 6:21pm

   
   

   I can see the appeal of going green, but for me, there is nothing like having an enormous hunk of metal between me and and the other cars on the road. I do my best to keep a gap of air in the way too :) but if that ever fails I trust in steel more than crumple zones and plastic bits, and no I don't particularly care what the numbers say.

    

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2.  

   

   Jay (profile), Apr 6th, 2011 @ 6:28pm

   
   

   Time Travel

   Time Travel is deemed impossible

    

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3.  

   

   Lawrence D'Oliveiro, Apr 6th, 2011 @ 6:40pm

   
   

   15%?

   Not sure how you get that 15% figure. Moving at a constant speed in a straight line, 100% of a car’s power output goes to overcoming friction.

    

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4.  

   

   Engineer, Apr 6th, 2011 @ 6:43pm

   
   

   Response to: Anonymous Coward on Apr 6th, 2011 @ 6:21pm

   You should look into things more, there have been huge improvements in car safety over the years, and the logic behind large steel frames being safe is totally flawed.
   
   Here's a quick video on topic: http://www.youtube.com/watch?v=joMK1WZjP7g

    

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5.  

   

   Anonymous Coward, Apr 6th, 2011 @ 6:55pm

   
   

   Re: 15%?

   You have to take into account lots of different types of friction, not just from the road. Air resistance, drive train efficiency, engine efficiency, heat energy and others have to be factored in. I'd be interested to see where that number came from though.

    

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6.  

   

   Roland, Apr 6th, 2011 @ 8:53pm

   
   

   google "henry ford hemp car"

   I'm surprised no one mentioned this yet:
   http://www.hiddenmysteries.org/conspiracy/facts/fordhemp.html
   "Ford demonstrated the strength of the car body by smashing an ax against the trunk, only to have it bounce off."
   Also http://hempcar.org/ford.shtml

    

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7.  

   

   Anonymous Coward, Apr 6th, 2011 @ 9:27pm

   
   

   Re: Response to: Anonymous Coward on Apr 6th, 2011 @ 6:21pm

   Though that maybe true to some extent, many of those safety crash tests are now conducted under slower speeds than what they used to be conducted under and they get similar results (I remember hearing somewhere that the testing speed standards changed and were lowered). and read the comments of that video for more insights into that test.

    

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8.  

   

   Anonymous Coward, Apr 6th, 2011 @ 9:51pm

   
   

   Re: Time Travel

   To bad I wanted to go back when there was no copywrong.

    

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9.  

   

   Chris in Utah (profile), Apr 6th, 2011 @ 9:52pm

   
   

   Re: google "henry ford hemp car"

   May want to completly do your car in hemp considering it grows 3 times faster than corn for fuel as well.

    

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10.  

    

    Pixelation, Apr 6th, 2011 @ 10:26pm

    
    

    "The air bubbles have to be really really small, though,"
    
    All we need are millions of really, really tiny people to blow those bubbles.

     

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11.  

    

    Lawrence D'Oliveiro, Apr 7th, 2011 @ 2:16am

    
    

    Re: 15%?

    You have to take into account lots of different types of friction, not just from the road.
    
    I didn’t say it was just from the road.

     

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12.  

    

    Pixelation, Apr 7th, 2011 @ 3:03am

    
    

    Re: Re: 15%?

    I sense some friction between you two.

     

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13.  

    

    Michael Ho (profile), Apr 7th, 2011 @ 10:00am

    
    

    Re: 15%?

    Several estimates put it at around 15%, including the US gov:
    
    http://www.fueleconomy.gov/feg/atv.shtml
    
    That site explains it in most detail:
    
    In gasoline-powered vehicles, over 62% of the fuel's energy is lost in the internal combustion engine (ICE). ICE engines are very inefficient at converting the fuel's chemical energy to mechanical energy, losing energy to engine friction, pumping air into and out of the engine, and wasted heat.
    
    Advanced engine technologies such as variable valve timing and lift, turbocharging, direct fuel injection, and cylinder deactivation can be used to reduce these losses.
    
    In addition, diesels are about 30-35% more efficient than gasoline engines, and new advances in diesel technologies and fuels are making these vehicles more attractive.

     

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14.  

    

    Lawrence D'Oliveiro, Apr 7th, 2011 @ 7:45pm

    
    

    Re: 15%?

    But remember Newton’s First Law: a body doesn’t need any energy input to maintain a constant velocity.
    
    So at a constant velocity, all the engine’s output is being used up in friction.

     

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15.  

    

    Anonymous Coward, Apr 7th, 2011 @ 8:36pm

    
    

    Re: Re: 15%?

    I was thinking the same thing.
    
    One may argue that a heavier car requires more energy to maintain a constant speed regardless of exposed surface area and aerodynamics, but that's only because a heavier car creates more surface friction along the imperfect road/surface. If you were on a frictionless surface (ie: while ice isn't frictionless, skis on ice have less friction than cars on pavement) then the energy required to maintain a constant speed wouldn't depend on weight nearly as much.

     

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16.  

    

    Anonymous Coward, Apr 7th, 2011 @ 8:37pm

    
    

    Re: Re: Re: 15%?

    but that's mostly because * (I hate to make absolute statements).

     

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17.  

    

    Anonymous Coward, Apr 7th, 2011 @ 8:52pm

    
    

    Re: Re: Re: 15%?

    For example, try gently sliding your hand across the surface of your table. It's easy. Now push your hand down into the table as hard as you can and try sliding it across the surface. Maintaining a constant speed is more difficult.
    
    Sure your hands aren't on wheels, but even if you performed the same experiment with a hot wheel (gently roll the car across the surface vs pushing down hard and rolling it across the surface) the result will be that pushing it down requires more energy to maintain a constant speed. Somewhere along the line, the extra weight of (or applied to) the car produces more friction.
    
    Much of that is also dependent upon the smoothness of the surface as well. For example, it would generally be much more difficult to overcome a bump on the road if there is more weight vs if there is less weight, especially if it's a sharp bump where the gain in potential energy due to moving up is lost as a result of the vehicle moving straight down in opposed to moving down over a smooth slope.

     

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18.  

    

    Anonymous Coward, Apr 7th, 2011 @ 9:09pm

    
    

    Re: Re: Re: Re: 15%?

    and, in fact, if a heavy vehicle hits a bump vs a light vehicle hitting an identical bump, my guess is that both vehicles will be slowed down by about the same amount. but the key here is that the big vehicle will apply more force to the bump than the small vehicle and so more kinetic energy is lost and it will take more energy to bring/accelerate the big vehicle back to its previous speed than it would the small vehicle.

     

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19.  

    

    Anonymous Coward, Apr 7th, 2011 @ 9:11pm

    
    

    Re: Re: Re: Re: Re: 15%?

    (and, in a sense, the big vehicle could also be said to be applying more force to the air molecules around it and so more kinetic energy is lost due to that friction as well? Would you rather get hit by a big truck at 30mph or a small car).

     

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20.  

    

    Anonymous Coward, Apr 7th, 2011 @ 9:25pm

    
    

    Re: Re: Re: Re: Re: 15%?

    So, to summarize any(?) imperfection that results in friction will cause a heavier vehicle to lose more kinetic energy than a lighter vehicle and so the required acceleration energy to overcome that loss in kinetic energy and maintain a constant speed is hence greater for a heavier vehicle than a lighter vehicle.

     

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