What does the moi feel like?

[Don A. Gilmore]

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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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