Key Leads and Inertia

[Farrell]

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Comments below:

Terry Farrell
 =20
----- Original Message -----=20
From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
To: <pmc333@earthlink.net>; "Pianotech" <pianotech@ptg.org>
Sent: Friday, April 25, 2003 3:11 AM
Subject: Re: Key Leads and Inertia


> Paul McCloud wrote:
>=20
> > John:
> >         I fail to see what this has to do with real-world dynamics.
> > Since the lead is integral with the keystick, not suspended by a =
thread,
> > the inertia is going to be the same no matter how much acceleration =
is
> > generated by the pianist's finger.  What am I missing?
> >         Paul McCloud
> >         San Diego
>=20
> I've wondered about this two, scratching my head a bit. But taking =
things at
> face value I do have a couple questions if somebody has the answers =
handy.
>=20
> 1. Isnt this question about lead in the key really about its total =
mass, and
> if you first were going to conceptually <<de-couple>> the lead mass =
and
> dangle it on a string, wouldnt you have to do that for the wood mass =
as well

Well yes, but...... John is trying to demonstrate what the addition of =
lead to a key makes. The key with no lead with have certain inertia =
characteristics. The key with the lead will have different inertia =
characteristics. Comparing the force required to push the key down =
slowly (less than the acceleration due to gravity) with no lead and with =
the lead will reveal that less finger force is required when you have =
lead in the front portion of the key. Comparing no lead and lead when =
applying a forte blow (much greater acceleration than that due to =
gravity), it will require more force applied to the key with the lead to =
accelerate the key at the same rate as with no lead. Decoupling the lead =
in the diagram is simply to help visualize this phenomena.
=20
> 2. How fast is the approximate fastest we could expect the key to be
> accelerated by human fingers in the first place ?

Lift the front of the key up. Drop it. That is the acceleration due to =
gravity. A forte blow is many times (est.) the acceleration rate due to =
gravity.
=20
> 3. Exceeding 980/sec^2 just means you are not getting any more =
<<help>> as
> it were from the force that is gravity. But this isnt the same as =
saying
> that doing so somehow creates an increase in resistance to
> acceleration....yes ?? Its not like gravity has a kind of reverse gear
> affect here.

No, gravity does not change, it is an acceleration force that is =
consistent. The pianist is the one that is applying an additional =
acceleration force. If the finger force is less than that of gravity, =
adding lead to the key will decrease the amount of force required to =
push the key down at some acceleration rate less than that of gravity. =
If the finger force is greater than that of gravity, adding lead to the =
key will increase the amount of force required to push the key down at =
some acceleration rate greater than that of gravity.
=20
> 4. From your (Johns) diagram about how to figure Inertia I have a =
question
> that goes along the same lines. Seems like it would be better to =
measure
> points independant of lead placement, and rather symetrical accross =
the
> front half of the key... or what ?

Perhaps I missed something (did I?). Did someone post regarding =
calculating inertia? Could you repost? (Please!)?=20
=20
> Cheers
> RicB
>=20
> --
> Richard Brekne
> RPT, N.P.T.F.
> UiB, Bergen, Norway
> mailto:rbrekne@broadpark.no
> http://home.broadpark.no/~rbrekne/ricmain.html
>=20
>=20
> _______________________________________________
> pianotech list info: https://www.moypiano.com/resources/#archives
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