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About shapes and rotation...

  1. Jan 29, 2016 #1
    I am aware that this could be the wrong section for this, but I wish to ask this here if you all don't mind. You all know how a sphere rolls along the ground easier than a cube, right? Well, how are the physics of motion involved in why a sphere rolls easier than a cube, or an irregular object?
     
  2. jcsd
  3. Jan 29, 2016 #2
    When a sphere rolls its centre of mass stays at a constant height above the surface.
     
  4. Jan 29, 2016 #3
    What about other shapes?
     
  5. Jan 29, 2016 #4
    It doesn't (apart from a cylinder and similar shapes).
     
  6. Jan 29, 2016 #5
    Well, if that is that, then thanks. I appreciate the help.

    Wait, in the case of both spheres or other objects, the CoM still follows a straight line, right?
     
  7. Jan 29, 2016 #6
    Yes I guess that's it - there's not much more to say really, except that moving the centre of mass of say a cube up and pivoting it around an edge takes energy; some of this energy is released when the cube "falls" over the pivot edge but then that most of that energy is lost in heat and perhaps sound when the cube lands on a face, then you have to put more energy in to lift the centre of mass again...
     
  8. Jan 29, 2016 #7
    And there is less energy to be used in a sphere, right?
     
  9. Jan 29, 2016 #8
    Only what is lost in friction.
     
  10. Jan 29, 2016 #9
    Okay then. I get it now. Thanks.
     
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