- #36
A.T.
Science Advisor
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Of course it could move radially towards the center. The string only prevents it from moving away radially.bobie said:The ball cannot move perpendicularly,
But that is completely irrelevant to work done. Work done on the ball doesn't depend on what the ball can do. It depends on what the ball is actually doing: If it moves perpendicular to the force, the force does no work. That follows directly from the dot product in the definition of work:
http://en.wikipedia.org/wiki/Work_(physics)#Mathematical_calculation
wikipedia said:[itex]W = \int_C \mathbf{F} \cdot d\mathbf{s} = Fs\cos\theta.[/itex]
In the notable case of a force applied to a body always at an angle of 90 degrees from the velocity vector (as when a body moves in a circle under a central force), no work is done at all