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Conceptual Question for Fictitious Forces

  1. Sep 18, 2012 #1
    1. The problem statement, all variables and given/known data

    Fictitious forces are created by people when motion is observed from non inertial F.o.r. what is the real cause of these fictitious forces?



    2. Relevant equations


    3. The attempt at a solution

    Since Fictitious force are viewed from non inertial F.o.r, the answer is basically in the questions, how would you explain?
     
  2. jcsd
  3. Sep 18, 2012 #2

    gneill

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    Staff: Mentor

    Can you elaborate on your attempt?
     
  4. Sep 18, 2012 #3
    Its just that from what I've been taught, fictitious forces are forces created from a non-inertial f.o.r., I just dont see the real causes of fictitious force.
     
  5. Sep 18, 2012 #4

    gneill

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    Staff: Mentor

    Then consider an object observed by two different observers, one in an inertial frame and one in a non-inertial frame. Both observers interpret their results assuming Newton's laws. How does each interpret the results?
     
  6. Sep 18, 2012 #5
    I think it is caused by fictitious motion(acceleration) of an object.
    The object is actually not moving at all but seen accelerated from noninertial frame.
     
  7. Sep 18, 2012 #6

    gneill

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    Staff: Mentor

    Okay. Now, the observer in the accelerated frame still wants to write equations of motion for the object. How is he going to interpret the apparent motion of the object?
     
  8. Sep 19, 2012 #7

    PeterO

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    Homework Helper

    We spend most of our lives in a frame of reference that is not accelerating [or not accelerating very much] so we adopt the non accelerating frame as our point of reference.

    When we suddenly find ourselves in an accelerating frame, we make up fictitious forces to explain away our perceptions.

    eg, You are in a car that suddenly accelerates away from the traffic lights. If you are going to remain with the car - some part of that car has to push you forward; usually the seat back.

    The only other time you would have felt the seat back push on you like that was when you braced your feet on the firewall - the vertical part of the cabin between the occupants and the engine - and pushed as hard as you could.
    You were not surprised, then, that following Newton's Third law:
    You pushed the firewall forward, so the firewall pushed you back. That push back meant you pushed back on the seat, so the seat pushed forward on you.

    Now you are sitting in the accelerating car, and the seat is pushing forward on you.
    That push is not originating from you pushing on the firewall, so your mind tells you something else must be pushing back on you - you invent a fictitious force to explain your sensations. You even invent a fictitious object as the source and are liable to say "Wow, that engine really pushed me back unto the seat!" And the engine wasn't even touching you!
    In normal situations the car will stop accelerating after a few seconds and you return to your non-accelerating frame of reference, where nothing is pushing you, and promptly forget the whole fictitious force - until the brakes are briefly applied and some strange "thing" tries to push you through the windscreen [like when your "friends" in the back seat pushed you forward to make you spill your drink last week].
     
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