Ball suspended on a string

Question

If you have a ball spinning on a string which is attached to a pole, will it keep spinning in the absence of any friction/air resistance/other retarding forces?
I'm trying to think about this in terms of Newton's First Law which suggests that the ball will keep trying to rotate, causing tension in the string and maintaining circular motion. Intuitively however it seems impossible that giving the ball a starting push would enable it to keep spinning around in a circle forever.
But on the other hand objects in orbit will continue to stay in orbit since the force of gravity is continually pulling them inwards whilst they continue to try and move in a circular orbit.
I would really appreciate any explanations to help me, at this point just very confused.

gandalf61 · Answer

In the complete absence of any friction/dissipative forces (i.e. no friction in the pivot, no air resistance, no flexing of the string) then conservation of energy says that once the ball has been started it will continue in motion for ever. The string constrains the ball's motion, but the force exerted on the ball by the string does no work since it is always perpendicular to the string's velocity, so the ball's energy does not change.
The reason this answer is not intuitive is that achieving a complete absence of friction is very difficult in practice. For a start, you would have to enclose the ball, string and pivot in a vacuum to eliminate air resistance.

Ball suspended on a string

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