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enter image description hereenter image description hereI was asked to draw a diagram of the forces acting on a ball in vertical circular motion when it is at a horizontal point.

I drew the weight of the ball acting straight down and the centripetal force acting horizontally towards the centre of the circle. The marking scheme included a third force the'reaction' acting vertically upwards. My questiong is where is this third force coming from? (I know it has velocity upwards but i don't see how this could be considered a force

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  • $\begingroup$ Can you draw a diagram and add to this question? And be clearer in what the mark scheme shows? From your description here you are perfectly right in what you did - there is no such 3rd force unless the question is missing information. $\endgroup$
    – Steeven
    Commented May 30, 2016 at 22:32
  • $\begingroup$ By the way, what exactly is a "horizontal point"? $\endgroup$
    – Steeven
    Commented May 30, 2016 at 22:32
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    $\begingroup$ I added pictures of the question and marking scheme $\endgroup$
    – Robert S
    Commented May 30, 2016 at 22:36
  • $\begingroup$ The key point that you missed is the work "uniform" in describing the motion.With your free body diagram will the motion have constant speed or not? $\endgroup$
    – dmckee --- ex-moderator kitten
    Commented May 30, 2016 at 22:45

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The picture of the man shows it.

  • Was it a ball on a string, then only pulling in the string is possible - no lifting. Then only a force towards the center (the pulling force) and gravity are present.

  • In this case, though, the person clearly lifts the ball. He pushes it upwards. Therefor we have an upwards pushing force as well.

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