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Car roll over

  1. Apr 24, 2014 #1
    Greetings

    Im trying to understand how a car, and other things for that matter, that moves in a circular motion is able to flip over? As far as I know the only force acting is the centriputal force acting on the tires and going inwards. Is it this force that can act as a moment around the cars center of mass causing it to flip? Is the straight line inertia of the car playing a role?

    Best Regards
     
  2. jcsd
  3. Apr 24, 2014 #2

    mfb

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    Yes. (Centripetal force)
    Classical mechanics would look completely different without, so... yes?
     
  4. Apr 24, 2014 #3
    Its just that the centriputal force is the only force i can "see" in my free body diagram. If the inertia plays a role in the moment around the center of mass then shouldn´t it be force?

    Best regards
     
  5. Apr 24, 2014 #4

    mfb

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    No, and I can't see a reason why you would assume this. The car in the curve is accelerating (and rotating if it flips over), clearly the forces (and momenta) are not balanced. Gravity is another force acting on the car, of course, but it does not lead to a torque around the center of mass.

    Still centripetal force without u.
     
  6. Apr 24, 2014 #5
    I just can´t see what forces..I know about the centriputal force, but what other forces (other than gravity) acts on the car?
     
  7. Apr 24, 2014 #6
  8. Apr 24, 2014 #7

    A.T.

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    It's not the only force. There are vertical forces at the wheels (normal contact forces), which are greater at the outer wheels. So in sum they create a torque that opposes the torque of the horizontal centripetal force (friction). The car flips over if the torque of the centripetal force is greater, than from the contact distribution.

    There are types of analysis where inertia is modeled as a force:
    - Quasi-static analysis
    - Analysis in a non-inertial frame
     
  9. Apr 24, 2014 #8
    From the non-rotating frame of reference, the centripetal force is applied at the wheels of the car, because the wheels are what grips the ground. The centripetal force is inward, and it pulls the bottom of the car inward toward the center. This creates a torque which rotates the car and causes it to flip over.

    From a rotating frame, there is a centrifugal force which pulls outward on every part of the car. On average, you can treat it as a force on the center of mass on the car, pulling outward. But the car is also attached to the ground at the wheels, so the centrifugal force creates a torque which flips the car over.
     
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