What does the moi feel like?

[Ed Sutton]

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Yes!  And isn't this "sluggishness" the "MOI" we've been talking =
about????

I know the image of the kids on the teeter-totter.  In fact, I've often =
used the image of elephants on the teeter-totter!

And I suppose in a blindfold test, I could tell by pushing if the =
teeter-totter was empty, or had the elephants in place.

But here we have been discussing the merits of placing two leads at the =
front of the key, or four at the back.  In principle this makes plenty =
sense, but in practice , we aren't dealing with anything like the degree =
of difference between the empty teeter-totter and the one with the kids =
or elephants.  We are dealing with very slight differences of key lead =
placement in piano actions, where most of the "sluggishness" we feel =
comes from the hammers.

"Sluggishness" is a powerful sounding word, but in a situation close to =
the zero friction, zero gravity experiment, do you think you could =
distinguish between the key with two leads at the front and the key with =
four at the back (located to produce identical frontweights) by pressing =
the key with your finger to produce different hammer velocities?

Ed Sutton
  ----- Original Message -----=20
  From: Don A. Gilmore=20
  To: College and University Technicians=20
  Sent: Monday, January 05, 2004 9:42 PM
  Subject: Re: What does the moi feel like?


  Hi Ed:

  All that would be left is the "sluggishness" of the parts, i.e. the =
tendency of the key not to want to move and not to want to stop moving.  =
The force required would be proportional to how quickly you try to =
change the speed of the key.  Incidentally, if you totally balance out =
the weight of the hammer, the key won't come back up to its starting =
position.

  Think about an ordinary playground teeter-totter.  With no one in =
either seat, it is easy to move it around and it stays where you put it. =
 Now put a fat kid on either end (both the same weight).  It's still =
balanced and stays where you put it, but it is much more difficult to =
start and stop it.  The fatter the kids, the more moment of inertia the =
system has.  To start one kid upward quickly takes a big heave.  Then if =
you want to stop him it is also difficult; in fact, he may actually lift =
you off the ground if he has enough energy at that point.  The feel =
would not be the same at all for an empty teeter-totter.

  Note that since the system is balanced, any disturbing force can tip =
the teeter-totter, no matter how small (neglecting friction).  I can =
drop a small brick in one kids lap and start the lever turning and it =
will accelerate faster and faster until he strikes the ground.  The key =
concept to realize is that the teeter-totter will accelerate at a =
greater rate if I drop the same brick onto it when it's empty than with =
two fat kids sitting in it.  If I put two 500-lb. slabs of concrete in =
each seat, the brick will accelerate them even less, though the system =
is still balanced.=20

  Don A. Gilmore
  Mechanical Engineer
  Kansas City
    ----- Original Message -----=20
    From: Ed Sutton=20
    To: College and University Technicians=20
    Sent: Monday, January 05, 2004 5:51 PM
    Subject: What does the moi feel like?


    Dear Physicists of the List-

    Please comment on this thought:

    When I press the piano key, the resistance to movement I feel =
consists of three elements
    1) Friction
    2) The pull of gravity on the hammer and wippen, partly =
counterbalanced by the pull of gravity on the keyfront.
    3) The combined MOI's of the various moving parts.

    Therefore, if I can=20
    1) reduce the friction to zero, and=20
    2) use a wippen assist spring to produce a balance weight of zero, =
the only resistance left would be=20
    3) the combined MOI's of the key, wippen and hammer. =20

    What I would feel then, in various key strokes, would be whatever it =
is we are talking about.=20

    Could I make or buy a gauge to measure this?=20

    Does this line of thought seem useful in understanding the =
situation?

    For example, has anyone felt a key such as I describe?

    Ed Sutton

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