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I Rotational Potential Energy?

  1. Oct 6, 2016 #1
    So masses on springs store potential energy. Height in a gravational field store potential energy for the mass there.


    So why isn't there a potential energy stored inside rotating objects? Surely there are ways to translate the rotational energy to kinetic. Its kinda like a spring. If a set down a fast spinning object, it will roll forward slowing its rotation down and speeding up its linear motion. One type of energy is transfered to another.
     
  2. jcsd
  3. Oct 6, 2016 #2
    rotations are described by 'kinetic' state - a change of configuration so why we seek a potential energy-
    potential energy is manifest in the position of bodies in a 'field'
    if one is sitting at the seventh floor of a building he has a potential to do work if he falls to the ground in earth's gravitational field- its not due to inertia of rest or motion.
    if the person is spinning as well as sitting on the sae height -what additional potential he developes- added energy is best estimated by his rotational energy which is 'kinetic ' in character.
     
  4. Oct 6, 2016 #3

    Dale

    Staff: Mentor

    I don't understand. It is already kinetic.
     
  5. Oct 6, 2016 #4

    CWatters

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    What Dale said. The energy rotational energy stored in a spinning mass _is_ kinetic energy. No need to "convert it".

    You can calculate it as..

    E = 0.5 I ω2

    where
    I is the Moment of Inertia (analogous to mass in a linear system)
    ω is the angular velocity (analogous to velocity in a linear system)

    See torsion spring. https://en.wikipedia.org/wiki/Torsion_spring

    14154-4703257.jpg
     
  6. Oct 6, 2016 #5

    CWatters

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    That might appear to be the case but you need to think about the whole system including the planet you are doing the experiment on.

    If you spin up a flywheel on the surface of the earth you affect the rotation of the planet (Newtons laws). There is no net change in the angular momentum of the combined planet/flywheel system. That's because there has been no external force applied to the system.
     
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