Why Can't a Conical Pendulum's String Be Horizontal?

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A conical pendulum cannot have a horizontal string because the tension in the string must provide a vertical component to balance the weight of the rubber bung. When the string is horizontal, the vertical force required to counteract gravity would be absent, leading to an imbalance. The necessary centripetal force for circular motion must always point towards the center of the circle, which requires a vertical component when the pendulum is in motion. Setting the angle θ to 90 degrees in the force equations reveals that the required forces cannot be satisfied, confirming that a horizontal string is not feasible. Therefore, the dynamics of circular motion necessitate that the string remains at an angle, not horizontal.
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Such as the figure
c47166411v146.png


Why the string could not be horizontal when the rubber bungis moving in a horizontal circle?
Only moving at conical pendulum?

By the way, if tension is equal to weight(W), have any conclusion?
 
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Why the string could not be horizontal when the rubber bungis moving in a horizontal circle?

Write an equation for the vertical forces acting on the bung. Set θ = 90 and see what happens.
 
What do you know about the force that is required to make an object move in a circle?
 
andrevdh said:
What do you know about the force that is required to make an object move in a circle?
centripetal force
 
Correct. That is the resultant force on the object needs to point to the centre of the circle.
In this case it means that the resultant of the two vectors must point to the center of
the circle. If the string could be horizontal where would the resultant lie?
 

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