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Q & A: Can you swing a ball around in a horizontal plane?

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Most recent answer: 05/31/2013
Q:
I'd like to know how one can explain the phenomenon of swinging a ball on a string above one's head. How can I explain the forces acting on the ball and its motion using Newtonian physics? I have no problem explaining the circular motion when the string is at an angle with the vertical and the plane of the motion is a horizontal that is below the point of suspension: The force in the string and the gravitational force creates a "net force" which supplies the centripetal force. But I have trouble explaining the circular motion of the ball and how it can stay up without sinking. Could you explain? Thank you very much in advance!
- Anna Werner (age 57)
Oakland, CA, USA
A:

Hi Anna,

You may have mispoken slightly, or perhaps I didn't understand your question.

I think you are wondering how it is possible to swing a ball above your head in a horizontal plane. In fact, this cannot be done (unless you go somewhere in space where there is no gravity).

There are only two significant forces on the ball: gravity and tension. On earth, the downward force of gravity can only be balanced if the tension has some upward component. If you tried to swing the ball horizontally around your head, there would be no upward component to tension, so gravity would provide a net force downward, and the ball would begin to fall.

Hope that answers your question!

David Schmid

 


(published on 05/31/2013)

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