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B Gravitational Potential Energy

  1. May 5, 2016 #1

    averycasille

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    Hello, I do not quite get this. Can anyone provide examples?
    " We may feel that it takes a force greater than the weight of the object being raised to lift it upwards, but it is not so. Provided the force is equal to the weight, the object will move upwards at a steady speed. "
     
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  3. May 5, 2016 #2

    jbriggs444

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    If you are riding an escalator upward, you feel the ordinary force of gravity. Your feet push down on the escalator with your normal weight and the escalator supports you by exerting an equal and opposite upward force.

    Of course, when you step onto the escalator there must be a momentary increased upward push and when you step off, there must be a momentary decreased upward push.
     
  4. May 5, 2016 #3

    sophiecentaur

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    I agree that this is not totally intuitive. I think that your problem is because in any practical situation there is friction (and stiction), which will 'naturally' slow things down and would require some small excess of upward force over the weight for the mass to keep rising. Plus, to accelerate the object in the first place, will require an excess force. Before Newton, people believed that everything naturally slows down, which was not totally unreasonable, in a world where even wheeled vehicles slowed down on the level, due to rubbish bearings and road surfaces. They believed that the Planets were being pushed around, for the same reason.
    Also, you have to keep pushing (to compensate for the loss in Gravitational Potential Energy.
     
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