What does the moi feel like?

[Don A. Gilmore]

This is a multi-part message in MIME format.

---------------------- multipart/alternative attachment
Well, I exaggerated the situation for the sake of emphasis.  Adding lead =
weights to the keys and/or moving them will change its moment of =
inertia. =20

Will it change very much?  Will you be able to detect the difference?

Well, that's why we have engineering units for m.o.i. (slug-ft^2, or =
kg-m^2) and a way to calculate it...otherwise we'd be shooting in the =
dark.  And if we know the moment of inertia before and after we add/move =
the leads, we can calculate a percent change to get a relative sense of =
what's going on.  That way we don't have to have a "feel" for how much a =
killogram-meter-squared is.

So, for example, if we calculate the m.o.i. with no weights and then =
calculate it again after we've added weights and the difference is a 20% =
increase, we can say that the mechanism is now 20% more sluggish, which =
would be much more noticable than if it were 0.01% more sluggish.  =
Obviously, putting a quarter in the fat kid's pocket is less "noticable" =
than putting a bowling ball in his lap.

You'll just have to do the math and see.  That's what engineering's all =
about.  The weights may be small and the key large, but the key is only =
wood and uniform; the weights are lead and concentrated away from the =
pivot point.  You may find out that they are negligible, or you may find =
that they have a profound effect.  I'm guessing that they'll be =
somewhere in between, but you won't know till you figure it out.

Don A. Gilmore
Mechanical Engineer
Kansas City
  ----- Original Message -----=20
  From: Ed Sutton=20
  To: College and University Technicians 'Subject: Re: What does the moi =
feel like?


  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
---------------------- multipart/alternative attachment
An HTML attachment was scrubbed...
URL: https://www.moypiano.com/ptg/caut.php/attachments/57/75/b2/14/attachment.htm

---------------------- multipart/alternative attachment--