Key Leads and Inertia

[Richard Brekne]

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John Hartman wrote:

> Richard Brekne wrote:
>
> >
> > Much has been made of the idea that more mass requires more effort to
> > move, yet at the same time it is ignored that once that mass is moving
> > it takes less effort to keep it moving. In reality these are flip sides
> > of the same coin and to some degree whats good about the one side is bad
> > about the other.
>
> Well not exactly. Acceleration (change in speed) not velocity (constant
> speed)is what you need to look at in the action. Acceleration is the
> change of velocity and it always requires force. While it's true that in
> strict physics it takes no force to maintain velocity (as long as there
> is no opposing force like friction or the pull of gravity) this is not
> much of a factor in regard to the pianos action. In order to play a note
> the key is accelerated from  0 velocity to some  greater velocity during
> a short period of time. There is really no time for the player to
> benefit from any momentum (mass time speed) that may happen in the
> action. While playing the action bits and pieces are accelerating or
> decelerating. I can't think of any time when a part is moving with
> constant speed except when the note is not being played at all.

I dont think we are talking absolutes here John. The question as to whether
players benifit from any momentum is more a matter of whether or not the
amount of acelleration after the initial movement requires enough force in
itself to be significant. If not, then it is surely that initial acelleration
and ensueing momentum that is the reason. If the degree of key acelleration
after say the first mm of key travel is very high, and continues to be very
high then perhaps this is important. On the other hand, if the finger gets the
key moving within say 90 % of its end speed right off the bat... then it is
perhaps much less important.

>
> Of coarse there is the escapement. But even a hammer flying free from
> the rest of the action feels restraint. It is being held back by
> friction and the pull of gravity. It is decelerating. This is why the
> let off is kept close to the string - the less of it the better. Any
> momentum the hammer has as it impacts the string was bought and paid for
> by the force applied to the key.
>
> > In answer to your querry, it is my guess that the reasoning for the
> > acellerated action has more to do with key motion after the finger gets
> > it moving, and after it rebounds of the keyfront cushion, as this is
> > where more inertia is more an aid then a hinder.
>
> No. More inertia does not help the key to rebound. When you play a note
> the key is accelerated till it stops (decelerates) on the front cushion.
> It must accelerate again to come back up.

I dont think I said that more inertia helps the key to rebound here, tho I
think I noticed that Newton did in that clip Cy refered us too. He said:

     "Steinway's "accelerated action" was nothing more than the use of
     the
     "moment of inertia" which in physics dictates that the weights start
     at
     the center or balance point to promote rapid return: faster
     repetition.
     At the expense of the pianists energy input."

My point was that I thought it was more because of the momentum aid then
because of anything else.

> Reducing the inertia (the resistance to acceleration) helps with both
> accelerating the key while playing and the acceleration of the key
> coming back up. It makes the action easier to play and faster as well.

I think we are bound to disagree here. To begin with... "easier to play" can
mean many things to many people, and given the varried argumentation I read as
to exactly this point relative to inertia its perhaps not so difficult to see
why. There is such a thing as too little inertia. And that in itself implies
that there must be a happy medium somewhere, which in its turn implies a
degree of preference that is bound to vary largely due to how each of us
perceives "easy to play" to begin with. As to "faster".... well heeellll....
grin.. I see Newton and Steinway were of a different mind.

Keep em comming John. I find your perspectives on all this really stimulating.
It has me thinking about lots of angles I havent looked at closely enough and
thats always a good thing. Its far too easy in this buisness to wake up
thinking you've already got something all figured out as it is.


> John Hartman RPT
>
> John Hartman Pianos
[link redacted at request of site owner - Jul 25, 2015]
> Rebuilding Steinway and Mason & Hamlin
> Grand Pianos Since 1979
>

--
Richard Brekne
RPT, N.P.T.F.
UiB, Bergen, Norway
Piano Technician since 1974
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html


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