[Physics] Does perfectly horizontal circular motion exist in this example


The scenario I am putting forward is something like this:enter image description here

Can the string really be perfectly straight and horizontal as shown in the picture(i.e can perfectly horizontal circular motion exist)or is it just an ideal situation?

Secondly what force is acting on the ball/stone which is balancing the weight of it in the downward direction,and stopping is from falling?

Best Answer

As you suspect the wire cannot be perfectly horizontal nor, if its weight is considered, perfectly straight. At any point in time there are two forces acting on the ball,( ignoring the weight of the rope) : gravity (mg) and the tension due rope .

The vector sum of these must be equal to $mv^2/r$ in the radial direction. To counter the vertical gravitational force, the tension force must have an opposite vertical component hence the rope cannot be exactly horizontal.

The faster the mass is spun around, the smaller will be the angle . Also, in the absence of resistive losses, the motion of the mass is perfectly horizontal. The same is true if the losses are exactly balanced by the boy swinging the rope.

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