Touchweight was Cockeyed hammers / Don Gilmore

[Don A. Gilmore]

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Hi Richard:

You're confusing a lot of terms.  Inertia is not a quantifiable property =
of anything, it's an effect.  It's not an adjective, it's a noun.  You =
don't add or subtract inertia from anything.  It's just a scientific =
property.  I think what you are thinking of is just mass and moment of =
inertia.  Mass is the quality of an object that causes it to resist =
being accelerated.  Moment of inertia is the "rotational" equivalent of =
mass and is the quality of a rotating object that causes it to resist =
angular acceleration (speeding up or slowing down of rpm).  The moment =
of inertial is different from mass since it takes into acount the =
distribution of matter.  In other words, the more material that is =
further from the pivot point, the harder it is to accelerate (or =
decelerate) the object.  That's why flywheels have most of their mass =
toward the outer perimeter.

Velocity is meaningless to inertia.  Only acceleration can =
produce/require a force.  Kinetic energy (mv^2 / 2) is simply a property =
of a moving object in terms of energy.  It has nothing really to do with =
inertia.  It is sort of a potential energy term and refers to how much =
energy the moving object could produce if you tried to stop it.  That's =
why we used it when the hammer struck the string.  The hammer, when =
moving, has usable energy.  To give it that energy we had to previously =
accelerate it to that speed.  To accelerate it requires force and that's =
where the properties of mass and moment of inertia come into play.  The =
more "massy" an object is, the more work you have to do and force you =
have to apply to accelerate it.

There's no free lunch in physics.  X amount of work done by your finger =
is going to produce X amount of energy in the hammer no matter what the =
mechanism looks like.

Don A. Gilmore
Mechanical Engineer
Kansas City=20
  ----- Original Message -----=20
  From: Richard Brekne=20
  To: Pianotech=20
  Sent: Saturday, December 20, 2003 3:06 PM
  Subject: Re: Touchweight was Cockeyed hammers / Don Gilmore


   =20
  "Don A. Gilmore" wrote:=20

     Hi Richard: I'm not sure what the qualifications of your "physics =
guy" are, but inertia is not even an engineering quantity.  There are no =
units of "inertia".  It is just a concept regarding the nature of =
matter.  All bodies with mass have inertia and tend to want to stay at a =
constant velocity and move in a straight line.

  Been thinking about this statement Don. No units of inertia. Fair =
enough... but a thing does have inertia, and in some sense it has to be =
measureable or calculable .... or else the concept is really =
meaningless.  Say you have a 20 kilo ball and you want to accelerate it =
from 0 to 10 m/sec. Whatever way you want to describe the work needed to =
do this has to somehow deal with the exact amount of inertia this ball =
has. If this wasnt true... then how could one speak of one thing having =
more or less inertia then another.=20

  Ok... so inertia according to you doesnt have a number per se... as =
far as I can see that makes three "definitions" of inertia by physics =
experts on the list here..=20

  1. Inertia is no quantity at all.=20
  2. Inertia is equivalant to mass=20
  3. Inertia is porportional to mass but porportional to velocity =
squared.=20

  Now honestly guys.... how are we to deal with how much or what range =
of inertia in the key is desirable for a given ratio and a give top =
action inertia... when we seemingly cant even agree on what inertia is.=20

  The term is used all the time to describe the amount of difficulty =
there is in changing the velocity of a thing. Whatever the term... we =
need to be able to find some <<ideal>> combination (in terms of finger =
work)  of mass and velocity (the keystick) required to accelerate =
another mass (the whippen) to a given velocity, so that it can in turn =
accelerate another mass (the hammershank) to yet another velocity. Some =
of this pre-ordained by the leverage ratios of the key, whippen and =
hammershank.=20

  So if using the term inertia is so problematic in this charge... lets =
not use it... just describe this <<ideal>> in the relevant quantities=20

  --=20
  Richard Brekne=20
  RPT, N.P.T.F.=20
  UiB, Bergen, Norway=20
  mailto:rbrekne@broadpark.no=20
  http://home.broadpark.no/~rbrekne/ricmain.html=20
  http://www.hf.uib.no/grieg/personer/cv_RB.html=20
   =20

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