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I am reading about circular motion and centripetal force. I can visualise why a person sitting in the cart will not fall at the top of a circular loop-the-loop at minimum velocity $v=\sqrt{gr}$.

Questions

However, I read that at the top of the loop, the passenger’s hair should not be hanging downwards. Instead it should be hanging upwards. Why is this so?

Additionally, if the above is true, does it mean if I were holding a string or a pendulum at the bottom of the loop, and as the cart moves to the top of the loop, the string or pendulum will actually be hanging “upwards defying gravitational pull” rather than downwards pointing towards the ground?

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  • $\begingroup$ If centrifugal force pushes you towards the seat why do you think it will not do the same for your hair or a string? $\endgroup$ Jun 6, 2021 at 20:22
  • $\begingroup$ Hello Adrian. Thank you for your response. However, isn’t centrifugal force not an actual force? $\endgroup$
    – IM_LOST
    Jun 7, 2021 at 11:41
  • $\begingroup$ It is called a pseudo force or fictional force because it describes a set of inertial properties rather than a direct action of its own force. But it describes a real action that cannot be ignored. $\endgroup$ Jun 7, 2021 at 14:00

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If you hold a string and if you let it rotate in a plane perpendicular to Earth, then if the velocity of the string is such that the string is under tension, then it looks as if the object on the string (as well as the string itself) experience a force upward that is bigger than the force of gravity pulling it downward. That is, it looks as if the string with the object hangs upward. If you sat stationary on the rotating object it looked for you as if upward was downward. Everything around you looked as if it moved in a strange kind of gravity field.

So if you would make a video of a person sitting in a looping cart you would see their hair change from hanging down (at the lowest point) to hanging up. It would look as gravity has reversed direction and magnitude.

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