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Trying to wrap my head around this..

Discussion in 'Model S' started by Sir Guacamolaf, Apr 6, 2017.

  1. Sir Guacamolaf

    Sir Guacamolaf The good kind of fat

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    Imagine there is a supercharger at the top of the hill. And a Tesla is charging there.
    So pushing current into the car, is electrons dropping from high to low (potential energy gain ~ gravity)
    The Tesla is now 50% charged, and starts rolling down the hill. And due to regen, it ends with 75% charge (lets say).

    Ignoring transmission losses, battery losses, did we just create energy?
     
  2. HankLloydRight

    HankLloydRight Fluxing

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    No, because you used energy to get to the top of the hill, which is stored as potential energy. That potential energy is converted to kinetic energy on the way down.
     
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  3. MarcusMaximus

    MarcusMaximus Member

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    I was about to reply the same thing, but honestly, potential energy due to gravity has always bugged me, as it seems to imply you have potential energy due to height above every single massive object in the universe.

    I think a better explanation is that at the same time the Tesla rolls down the hill, Earth is pulled "upwards", opposite the direction of gravity by the Tesla. That motion is just imperceptible because of the much greater mass of Earth. Energy isn't created because the kinetic energy vectors of the car and Earth cancel out.
     
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  4. HankLloydRight

    HankLloydRight Fluxing

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    But you do have potential energy because you had to spend energy to get up there in the first place-- you had to fight against gravity which takes energy... You get it back at kinetic energy when going down. Sure, you can say you pushed the earth away from you as much as the car pushed away from the earth, but that energy going up is converted to potential energy.
     
  5. AlexG

    AlexG Member

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    Laws of physics still apply on a top of any hill even if there is a Supercharger there :) So, the answer is no.
     
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  6. MarcusMaximus

    MarcusMaximus Member

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    Assuming, of course, that you didn't originate from the top of that hill. I've always found potential energy due to gravity to be missing something, since it implies I have tremendous amounts of potential energy due to my elevation above, say, the Sun. Or the supermassive black hole in the center of the Milky Way. Especially since, as I remember, potential energy is actually stored as increased mass(at the rate given by e = mc^2).
     
  7. FlyF4

    FlyF4 Member

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    I think you are pulling our :confused:leg on this one. It's a joke. right?
     
  8. Sir Guacamolaf

    Sir Guacamolaf The good kind of fat

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    Yes! But lets keep it going for a while please.
     
  9. Sir Guacamolaf

    Sir Guacamolaf The good kind of fat

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    Okay but from the specific point where the Tesla started at the top, to the point that Tesla came all the way down, as compared to an ICE .. the ICE actually reduced mass (fuel burnt off), and yet the Tesla, with the same mass, comes down with a fuller tank. Even if you do e=mc^2, Tesla is somehow creating energy, simply amazing!
     
  10. McRat

    McRat Active Member

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    #10 McRat, Apr 6, 2017
    Last edited: Apr 6, 2017
    You have it backwards. A battery gets filled up with bad electrons as you use them. Think of it like brake dust.
    A Supercharger sucks the dirty electrons out of the battery. So you want to be parked higher than the SC.
     
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  11. tchockie

    tchockie Member

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    NERD ALERT
     
  12. tchockie

    tchockie Member

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    Jk I also have a background in physics but particle/radiation mainly
     
  13. calisnow

    calisnow Active Member

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    No - you did not violate the law of conservation of energy (in a closed system, energy can neither be created nor destroyed - rather it can be converted from one form into another).

    The potential energy (generated by doing work to drive to the top of the hill against the force of gravity pulling you the opposite direction (ignoring friction)) of your Tesla at the top of the hill was converted into kinetic energy (motion down the hill caused by the force of gravity). In the process of rolling down the hill your car did work. W = FD. Work is force multiplied by distance. Force is mass multiplied by acceleration. The gravitational pull between two objects (your car and the earth) accelerated your massive car down the hill - this force of your car accelerating, multiplied by the distance you rolled, did work - which charged your battery.
     
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  14. calisnow

    calisnow Active Member

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    Bro not everybody got a chance to take college physics.
     
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  15. calisnow

    calisnow Active Member

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    You do have tremendous potential energy due to your elevation above the sun. It's rendered irrelevant by the much greater gravitational attraction between you and the earth. Gravitational attraction increases as two objects get closer. If, however, you and the sun were the only two objects in a closed system you would immediately accelerate toward each other.
     
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  16. Bluechip

    Bluechip Member

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    But what if the Tesla was never at the bottom of the hill before? Lets say the factory was at the top of the hill along with all resources needed to produce it. What about that one? Huh? :)
     
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  17. calisnow

    calisnow Active Member

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    :facepalm:
     
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  18. calisnow

    calisnow Active Member

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    @Sir Guacamolaf - I'm genuinely not sure if you are making jokes or you're being serious with your questions. People who took, say a year of highschool physics and then a year of undergraduate physics - have had to do so many problems with these fundamental equations that it seems incomprehensible that anyone could not instinctively understand the energy exchanges going on when machines do work.

    But if you did not get to specifically do a physics class then this stuff is not at all intuitive - so I at least am not making fun of you if you didn't study it already.
     
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  19. Sir Guacamolaf

    Sir Guacamolaf The good kind of fat

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    #19 Sir Guacamolaf, Apr 6, 2017
    Last edited: Apr 6, 2017
    Well that's easy! The factory is powered by solar energy. So all those photons weigh down the factory a lot, and as a result, all potential energy gain is transferred to Model S's and X's rolling down the hill. Think of these cars as photon trucks (new license plate anyone?).

    So imagine the theoretical scenario that Elon sets up the next Tesla factory on top of a hill, and Tesla's roll down, guided by autopilot of course, they'd end up at our homes fully charged. This could of course be nullified completely by the sun's gravity, so all deliveries would have to be at night time, which I don't mind, since the car is silent!
     
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  20. HankLloydRight

    HankLloydRight Fluxing

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    I think the practical answer to @Sir Guacamolaf's question is that it depends on how many alternators are installed on the car.
     
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