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

Isn't heat production a kind of work?

  1. Aug 9, 2011 #1
    One often read in coursebooks that no work is done when (a living human is) holding a (heavy) weight. But is there not microscopic work done when you are standing there shaking like jelly. You have become a little power plant and power plants do work, don't they? There is a certain power, energy per time unit, and creating energy is work, isn't it?
  2. jcsd
  3. Aug 9, 2011 #2
    The text books are specific to work being done on the weight, not the air molecules around you. You are correct, work is being done on the air molecules because you are applying a force to them and they are moving.

    In the case of the weight you are applying a force however it is not moving since gravity is working destructively against you, no work is accomplished.
  4. Aug 9, 2011 #3


    User Avatar

    Staff: Mentor

    It's a difference between input and output. It takes a lot of input work to hold your muscles steady, but you are doing no output work on the weight you are holding. You might say that in that situation, your body is 0% efficient.
  5. Aug 10, 2011 #4
    Ok, so there is not only work done, but even useful work. Because air molecules of higher temperature will rise up and overcome gravitational potential. And therefore create a force times distance, which is work by definition. But there is no work done on the weight.

    I wish the books could be more clear on this point. Thanks for replies.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook