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Example of kinetic force > static force

  1. Jun 17, 2011 #1
    Can someone give me an example of a case where kinetic force would be greater than static force? Thanks.
     
  2. jcsd
  3. Jun 17, 2011 #2
    Any object travelling faster than 0.866c will possess kinetic energy greater than it's own rest energy (if this is what is meant btw).
     
  4. Jun 17, 2011 #3
    If I understand your question correctly then friction would be an example of a static force. It exists regardless of whether an object is moving or not. Drag would be an example of a kinetic force. It is only experienced by objects that are moving through a fluid or gas. As to whether one is greater than the other that depends on the situation.
     
  5. Jun 17, 2011 #4
    I expect you are referring to impact forces.
     
  6. Jun 17, 2011 #5
    In general a static force is a resistance between two forces.

    static force = mass
    static force = friction
    Skateboard going down hill.

    static force = tensile strength
    A weight that breaks a rope used to suspend it.

    static force = shear strength
    Scissors cutting paper.

    static force = gravity
    An airplane in flight.
     
  7. Jun 17, 2011 #6
    I'm an idiot, I apologize. I meant friction.

    So to rephrase my question: Can someone please provide an example where kinetic friction > static friction.
     
  8. Jun 17, 2011 #7

    rcgldr

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    I'm not aware of any solids that have this behavior, although the static and kinetic friction can be close for some cases, like teflon on teflon, with a coefficient of about 0.4 for both.

    There are control mechanisms called slide rails that use a fluid between the rail and a slider. The presence of the fluid results in resistance to movement that increases with speed, to elminate jerky movements for precise control. Some of these maintain the fluid by pumping the fluid through holes in the rail. This isn't really a case of static versus dynamic friction though.
     
  9. Jun 17, 2011 #8
    Thank you.
     
  10. Jun 17, 2011 #9
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