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I am wondering if a rotating sphere placed with a pipe/duct with air flowing through the pipe will cause the rotating sphere to experience a lifting force due to the Magnus Effect.

Moreover, if the rotating sphere does experience a lifting force due to the Magnus Effect, would this force result in the pipe/duct experiencing a net force in that direction, or will there be some kind of counteracting force that will cancel out the lifting force created by the Magnus Effect?

To illustrate my idea of how a rotating sphere could be rotated within a pipe/duct, I have created a 3D CAD drawing and this drawing is shown below in two viewing perspectives. An axial fan could generate the air flow through the pipe and the rotating sphere could be rotated by an electric motor (not shown in the drawing).

enter image description here

enter image description here

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  • $\begingroup$ Short pipe - potentially, by (on the average) deflecting the exhaust stream from the pipe down. Infinitely long pipe (or recirculating pipe) - no. $\endgroup$
    – TLW
    Commented May 9, 2022 at 0:24

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Yes, the sphere will experience a magnus force, and therefore give an upward force on the pipe.

But the way it gets that upward force is by (net) deflecting air downward, which would give a downward force on the pipe as more molecules hit the bottom surface.

Between that and the sphere, the net force on pipe is 0 - there is no self propelling pipe.

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  • $\begingroup$ I was thinking that this would be the case, but I wasn't sure about it, so I thought it would be worth asking the Physics community about it. $\endgroup$
    – user300400
    Commented Sep 24, 2021 at 20:40

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