Keys and MOI - wipp assist

[Fred Sturm]

	I haven't really been putting my question quite clearly enough, I don't 
think. Let me try from a different perspective.
	We have a (relatively) balanced system, each side having mass. The mass is 
acted on by gravity, hence there is an accelerating force at play on both 
sides. Additional force is needed in front to overcome the gravitational 
force exerted on the higher mass (leveraged) of the back. In a sense, the 
force exerted by gravity, and the force applied by finger or spring or 
magnet can be looked at as equivalent.
	On the other hand, the mass on both sides of the fulcrum has inertia, 
which can be measured in terms of moi. I think that one way of looking at 
this inertia is to call it resistance to force, or resistance to 
acceleration. It will require force to set the system into motion, and the 
acceleration will be limited by a balance between force applied and moi.
	In terms of accelerating an action to make musical tone, the gravitational 
forces at play are insufficient to reach adequate velocity for more than a 
piano blow, because gravity is directly connected to distance. The force 
exerted by springs or by magnets is not distance connected. Hence, it can 
aid in acceleration to velocities exceeding that of gravitational fall.
	So, in the dynamic process, would not a force of this sort, present in the 
system at all times, have some effect on the perception of inertia, as it 
aids not only in counterbalancing gravity, but also in accelerating to a 
higher velocity?
	Maybe not, and maybe this is an insignificant quibble brought on by too 
many quick tunings for our All-State festival that starts tomorrow (huff, 
puff). But I guess I'm not entirely convinced that springs and magnets (as 
currently used in pianos) are equivalent to negative gravity - the 
reciprocal of mass. It seems to me that there might be additional 
considerations.
Regards,
Fred Sturm
University of New Mexico

--On Tuesday, January 6, 2004 8:56 PM -0500 John Hartman 
[link redacted at request of site owner - Jul 25, 2015]

> Fred Sturm wrote:
> The issue is whether these two means of reducing mass as
>> measured at the key have an effect at all levels of acceleration.
>
> Fred,
>
> Think about it this way; with the springs, what you put into them is what
> you get out. When the key comes back up after a note is played the spring
> is loaded. When you push the key down the energy is released. You store
> potential energy and you release it. It has the same effect at all
> dynamic levels.
>
> I think of helper springs as the same thing as balance weight except it
> is a negative quantity. Let's say we have an action with a wip spring. it
> is set up so there is a balance weight of 45 gm when the spring is not
> attached. When the spring is attached the balance weight goes down to 35
> gm. The force that just begins to move the key will be:
>
> 45*980gm/sec^2 - 10*908gm/sec^2
>
> After this force is applied to the key any additional force used to move
> the action will answer to the the inertia of the rotating parts (assuming
> there is no friction or other factors).
>
>
> 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
>
> Piano Technicians Journal
> Journal Illustrator/Contributing Editor
[link redacted at request of site owner - Jul 25, 2015]
>
>
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