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!

Basic question about defining work

  1. Jun 5, 2015 #1
    I know this will involve a simple answer but I just can't get it atm.

    work = force X distance and has units of Joules ie energy

    when I hold a bucket of water elevated so arm is parallel to the ground I have done some work.

    I now hold it out there and my arm muscle burns and fatigues fighting gravity ie I am metabolising energy to hold the bucket yet the bucket has moved no distance hence W = Fx0 =0 but I am definitely expending energy????
     
  2. jcsd
  3. Jun 5, 2015 #2

    Drakkith

    User Avatar

    Staff: Mentor

    You are expending energy because the human body is an imperfect machine. The energy is spent contracting you muscles fibers over and over again and is eventually dissipated as heat. That's how your muscles work and why it is impossible to hold something perfectly steady. If you replaced your arm with a metal bar, then no energy would be expended.
     
  4. Jun 5, 2015 #3
    so W=FxD still holds if you calculated the movement of the muscles?

    I am not suggesting anyone would do the calculation but just saying?
     
  5. Jun 5, 2015 #4

    Drakkith

    User Avatar

    Staff: Mentor

    I believe so, but I don't know how to apply a work equation to a stretching muscle fiber.
     
  6. Jun 5, 2015 #5
    elastic energy equation?
     
  7. Jun 5, 2015 #6

    Dale

    Staff: Mentor

    You would have to go down to the level of the actin and myosin. It uses the energy in ATP to trigger a little "ratchet" movement which exerts a force over a distance on a molecular scale.
     
  8. Jun 5, 2015 #7
    gotcha
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Basic question about defining work
Loading...