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On 2021/Jul/18, at 08:28, Brian Whatcott <betwys1@sbcglobal.net> wrote:
...but wait a moment; if a constant energy input per beat is provided, like bc describes, WHY is Q reduced as shown by reduced amplitude?The factors in play are air drag and pivot friction, so it is plausible to suggest that increased mass increases air-drag cross-section and/or total surface area of the bob, and increased weight increases pivot friction.
An experimental arrangement where mass is added to an internal bob cavity or the pendulum is situated in an evacuated tube, and where the slope of pivot friction versus weight is reduced by providing an air bearing or possibly a magnetically floated pivot point - might well shed light on this.
About pivot friction, it is well known that rolling friction tends to be less than sliding friction, so that a stiffly supported pin roller bob, pivoting on a stiff hard plane mount might well provide a higher quality factor Q. This method would have been accessible to clock makers for hundreds of years, so I expect it has more deficits than the fragility to bumps that is easy to imagine.
On Sunday, July 18, 2021, 09:36:32 AM CDT, Brian Whatcott <betwys1@sbcglobal.net> wrote:
BC's elucidation of his conditions for finding that increased mass reduces pendular amplitude reveals that he did in fact add mass at the location where bob velocity would be greatest, as Bob and I surmised.
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