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!

Conversion of KE when a force does not do work

  1. Sep 15, 2014 #1
    All energy is conserved.
    So if I push on an object and it doesn't move, where does that energy go?
  2. jcsd
  3. Sep 15, 2014 #2


    User Avatar
    Gold Member

    That can only happen when you have static friction and in such a situation, the energy is converted to heat through friction and is distributed among different parts of the environment and the object. The whole energy is conserved but not the object's energy.
    But when you say a force doesn't do work, it can mean something else too. You may have magnetic forces([itex] q\vec v \times \vec B [/itex]). It does no work because its always perpendicular to velocity. The particle's energy is conserved here.
  4. Sep 15, 2014 #3


    User Avatar
    Staff Emeritus
    Science Advisor

    Your body is not a very efficient machine. In this case, all of the energy you expend is used to tighten your muscle fibers, which stretch under the applied force. This means that all of the energy goes into stretching your muscles, eventually turning into heat, and none of it goes into moving the object.
  5. Sep 17, 2014 #4


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    What energy?

    Simply pushing on a stationary object doesn't give it any energy. It might feel like hard work but that's only for the reason others have given....namely that humans are not ideal machines. We are quite inefficient and consume energy even when not doing useful work. Much of that energy escapes as heat.

    If you use a spring to push on the same stationary object you will find no energy leaves the spring. It all stays stored in the spring.
  6. Sep 17, 2014 #5


    User Avatar
    Science Advisor

    Static friction is not dissipating energy as heat. Sliding friction is.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Conversion of KE when a force does not do work