1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    Science Advisor
    Gold Member

    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


    User Avatar
    Science Advisor

    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook