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I have a few questions about the joule/newton

  1. Jul 31, 2014 #1
    Im not quite sure what it is about this simple concept that i cant get, but im having a very tough time understanding how the concept of a joule makes sense.

    How can it be the energy expended in applying a newton through a distance of 1 meter?

    Isnt a newton just a measure of force? So it could represent accelerating a 1kg object by 1 metre per second, but couldnt it also represent accelerating a 5kg object by .2 metres per second?
    If that's the case, then what does it mean to apply a newton through a distance of 1 meter? Is that only relevant in cases where the weight is 1kg? Because applying a newton to a 5kg object over 1m would be alot more work than that required to do s with a 1kg object
  2. jcsd
  3. Jul 31, 2014 #2


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    No it wouldn't. The force is the same, and so is the distance, so work must the same also.

    To get a feel for it, think in terms of kinetic energy gained(ΔEk=W).
    In the first case, you end up with a heavier object moving slower than the lighter object in the latter case.
    The kinetic energy of the 5kg body accelerated by 1 Newton (with 0.2m/s^2 acceleration according to F=ma) over 1m will be the same as the kinetic energy of the 1kg body accelerated by 1N(a=1m/s^) over the same distance.
  4. Jul 31, 2014 #3
    It literally means you keep pushing with the force 1 N for however long as it takes to travel a meter. It isn't the same as accelerating the object by a certain amount per time over a meter.

    As Bandersnatch shows, applying 1 N to a 5 kg object over 1 m would accelerate it a lot less than 1 N applied to a 1 kg object over the same 1 m.

    Imagine expending the same effort throwing a light ball and heavy one. Or imagine taking an engine from a car and putting it in a big truck.
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