Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Question about the significance of negative work

  1. Sep 14, 2012 #1
    I am having some trouble understanding the significance of negative work.

    If the work that I do on object X is W, is it equivalent to saying that object X does work on me equal to -W ?

    After all, work is scalar, so I can't fathom the physical significance of negative work.

    Also, according to the work-kinetic energy theorem, due to the way in which work and kinetic energy are both defined, when I do work W on an object X, its kinetic energy increases by W and my energy decreases by W. Isn't that equivalent to saying that the object did work of -W on me, since at least in terms of kinetic energy the two are equivalent?

    All help on my understanding of this concept is appreciated.

  2. jcsd
  3. Sep 14, 2012 #2


    User Avatar
    Gold Member

    Yes, what you stated is correct. The object does negative work on you. In a sense, the negative means that energy has been taken FROM the object in question (aka you). Remember, scalars can be negative! They just can't have direction. You might be confused because people in the early stages of physics courses will say that speed is a scalar and velocity is a vector, the former being unable to be positive, but this is specifically because of the way speed is defined; it is not a general property of scalars. I assume this is where the confusion lays?
  4. Sep 14, 2012 #3
    OK I get it so far. So if object A does work W on object B, then that is perfectly equivalent to saying that object B does work -W on object A?

  5. Sep 14, 2012 #4
    That is correct.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook