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Thread: Is centrifugal force false?

  1. #1

    Is centrifugal force false?

    Is centrifugal force a false force?
    Because if one swings a can in a circle
    and releases it at the exact position, the centrifugal force should carry it directly to the right. But in real life, it does not, it travels tangent to the circle in which it was swinging.

  2. #2
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    There is more than one rotational force associated with swinging a can on a string that will explain the release trajectory.

    Centrifugal force, net force of a jet engine, epicyclic gear theory, hmmmmmm, if it quacks like a duck and it walks like a duck, it must be ????-????

  3. #3
    Principle Engineer
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    First of all, there is NO centifugal force, there IS a centripetal force that is directed toward the center which keeps the can on a circular path; it is opposite of the socalled centrifugal force.
    When you let the string go, there is now no force keeping the can in the circular orbit and according to Newon the can should continue in the direction of motion, in this case tangent to the circle.

  4. #4
    If there is no centrifugal force and centripetal force is the only action force on the object, what is the reaction force then to the centripetal force.

  5. #5
    Technical Fellow jboggs's Avatar
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    IMHO - Forget the terms centrifugal and centripetal. They are convenient explanations for real forces but their definitions fall apart in strict physical analysis. Force is force, regardless of its direction. The mass on which it acts accelerates in that direction. A moving mass will move in a straight line unless acted upon by some force. If that force is perpendicular to the direction of the mass's momentum, and it remains perpendicular to that momentum, the result is a circular path.

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    IMHO - Forget the terms centrifugal and centripetal. They are convenient explanations for real forces but their definitions fall apart in strict physical analysis."

    With all due respect , centripetal force is a REAL force and centrifugal is NOT; the latter is used as a convenience --D'Alembert reversed effective force to make a dynamic situation act like a static one using laws of equilibrium. For example, if you wrote a simple dynamic equation

    F=Ma and rearranged the equation to
    0=-F +Ma

    you have now made the dynamic equation static and -F becomes the D'Alembert "reversed effective force"

  7. #7
    Surely there must be another force that must be equal and opposite to keep the can in its path.
    You can call this force ‘centrifugal’ or whatever but it is a force that is experienced by the can trying to push it away from the centre of the circular path in which it is moving. I think it would be better to define it as the inertia of the can trying to push the can away. As anything moving in a circle is constantly accelerating according to Newton, the acceleration of the can creates an inertial force.
    Therefore, the force acting equal and opposite to centripetal force to keep the can in its path is an inertial force. Its magnitude is given by the the formula mv^2/r where m is the mass of the can, v is the speed of can and r is the radius of its path. Alternatively, F = mw^2r where w is the angular velocity.

  8. #8
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    You are very confused. I will try one last time.
    First of all, if the body is moving in a circular path the total forces on it cannot be zero, so your idea that "Surely there must be another force that must be equal and opposite to keep the can in its path." is false.
    You seem to be hung up on the proposition that all bodies have a zero net force on them which is simply not true in general; only those bodies moving at constant speed in a straight line and not being accelerated have zero net force on them. By that definition the body moving in a circular path has dV/dt ( V is a vector velocity) which not zero so by that definition it must have a net force acting on it. However, D'Alembert made the brilliant observation, as I pointed out previously) that you can fictitiously make the dynamic case a static one.
    I think you have a curious interest and should get your hands on a physics text that explains Newton's principles.

  9. #9
    Administrator Kelly Bramble's Avatar
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    gsalih,

    I think is healthy and eductational to challenge fundamental laws of physics. Though, in many cases where a fundamental law is well tested, one might spend more effort proving the laws of physics to be correct.

    Interesting discussion.

  10. #10
    I will be the first to admit that i have always been confused by centripetal/centrifugal forces. But how would you explain the force that is experienced by the can trying to push it away from its circular path.

  11. #11
    Technical Fellow jboggs's Avatar
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    The "force" (if you want to call it that) pushing the can away from its circular path is its own momentum. Mass will always travel in a straight line (not a circular one) unless acted upon by an outside force. The straight path is the natural one. A circular path can only be obtained by the continuous application of an unbalanced force. A circular path is really just a the natural result of a force pushing a mass in a direction perpendicular to the direction of its momentum. As the direction of its momentum continuously changes, so does the direction of the applied force.

    If you tie a string to a stationary can and pull it along in a straight path, the can will feel a force in that direction and accelerate. You will feel a force in the opposite direction. Both forces are the result of accelarating that can. If that can happened to be moving in a direction perpendicular to the string when you applied the force, it will accelerate toward the string. The result is a "circular" path. There is no force pulling it in the opposite direction.

  12. #12
    Project Engineer CCR5600Design's Avatar
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    Gettin' my learn on...

    Carry on.


    Ron

  13. #13
    It is a force, isnt it as anything moving in a circle is constantly accelerating anf F = ma

  14. #14
    Technical Fellow jboggs's Avatar
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    Your question was "would you explain the force that is experienced by the can trying to push it away from its circular path?"
    Not "would you explain the force that is experienced by the can keeping it on its circular path

  15. #15
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    "But how would you explain the force that is experienced by the can trying to push it away from its circular path. "

    What "force".; the only force on that can as it moves in a circular path is the tension in the string which pulls on the mass accelerating it towards the center, period. Do you see another?

    I am done with this thread and hope that you will get educated in dynamics as I suggested.
    Going on these forums will only confuse you more since some answers you get may not be accurate and some just not helpful.

  16. #16
    Yes, i see the inertial force due to inertia of the can but because it is not external force you may call it fictitious, false or does not exist.

  17. #17
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    I surrender!!!

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