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About the equation for net work done by nonconservative forces

  1. Apr 24, 2008 #1
    Wnc = delta (kinetic energy) + delta(potential energy)

    (Work done by nonconservative forces) = (change in kinetic energy) + (change in potential energy)

    Now, my professor gave us this formula instead of the one above: W - H = (change in kinetic energy) + (change in potential energy), where H = heat loss, W = work done.

    What I'm confused about is whether heat loss still counts as work....since the heat loss is caused by a frictional force such as air resistance, and the air friction would act opposite the direction of motion, so it seems that the air friction does negative work. so H still counts as work?

    Btw, for the first equation, its not assuming that there's no heat loss, right? (due to friction) So if its not assuming that there's no heat loss, then that would also include work done by friction (which would equal H in the second equation)? (negative work)

    Any help at all would be greatly appreciated..
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  2. jcsd
  3. Apr 24, 2008 #2


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    The first equation is completely correct. Any energy lost due to friction and heat will be manifested in a change in total energy (KE+PE), it's just not explicitly stated in the equation like in your other one. Heat loss does count as work, seeing as it is caused by a force (friction, or air resistance) applied through a distance. Indeed it is negative work, which means it takes energy out of the system.
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