Hi Richard, The moment of inertia, I, is: I = mr^2, where m = mass r = radius from axis of rotation I is additive, so if there are two masses, it's the sum. If you have a solid object, rather than point masses, you just have to calculate the integral. For a key stick (assuming it is a uniform stick, which it is not), the following might come close: I = [ m (f^3 + b^3) ] / [ 3 ( f + b) ], where f = the length from the fulcrum to the front of the stick, and b= the length from the fulcrum to the back of the stick m = mass of the entire unweighted stick, with capstan removed. You can add in inertia from lead weights and the capstan, however appropriate. In reality, it's a lot more complicated. The stick is not uniformly shaped and has stuff stuck on it like buttons, and keytops. The general equation for a uniform stick rotating about its end (used to derive the above) would be: I = 1/12 mL^2, where L = the length of the stick. Anyway, it depends on the keystick. You'll have to measure, weigh, and calculate for yourself. Peace, Sarah ----- Original Message ----- From: "Richard Moody" <remoody@midstatesd.net> To: "Pianotech" <pianotech@ptg.org> Sent: Thursday, May 01, 2003 10:09 PM Subject: Re: Key Leads and Inertia > What is the formula? for inertia? > > ----- Original Message ----- > From: Don <pianotuna@accesscomm.ca> > To: Pianotech <pianotech@ptg.org> > Sent: Thursday, May 01, 2003 12:33 AM > Subject: Re: Key Leads and Inertia > > > > Hi Richard, > > > > The inertia goes up by the *square* of the distance from the > fulcrum--so > > yes three weights would likely have less inertia than *one* > farther from it. > > > > Run the numbers > > > > 30 grams x 1 cm from fulcrum = 30 > > > > 10 grams x 3 cm from fulcrum = 90 > > > > If I'm wrong please let me know *grin*. > > > > Regards, > > Don Rose, B.Mus., A.M.U.S., A.MUS., R.P.T. > > > > mailto:pianotuna@accesscomm.ca > > http://us.geocities.com/drpt1948/ > > > > 3004 Grant Rd. > > REGINA, SK > > S4S 5G7 > > 306-352-3620 or 1-888-29t-uner > > _______________________________________________ > > pianotech list info: > https://www.moypiano.com/resources/#archives > > _______________________________________________ > pianotech list info: https://www.moypiano.com/resources/#archives
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