What's all this I hear about Inertia ?

[Farrell]

----- Original Message ----- 
From: "David B. Stang" <stangdave at columbus.rr.com>
> There seems to be a lot of confusing talk in the piano tech world
> about "key inertia". I was confused, too, until I went back to my
> physics textbook and found:
> Inertia by definition means resistance to acceleration, and (at
> speeds lower than the speed of light or so) inertia and mass
> are identical.

They are not identical, but rather directly proportional.

> In summary:
>
> Two items of the same weight have the same inertia here on
> Earth. Period.

If force is applied in the same manner, yes.

> If a perfectly rigid key weighed 1000 pounds overall but were
> balanced to have a certain down-weight, it would behave and feel
> the same as any other rigid key with the same down-weight.

No. Of two keys of different mass and the same down-weight, the one with the 
larger mass will have more inertia. The larger mass key will require more 
energy/force to move it at the same rate of the lighter key.

> But we all know that a key with less weight in front has more
> dynamic range.

Wow - what's dynamic range? I know what kynamic range means in general, but 
the dynamic range of a key?

> The key, pardon the pun, is the rigidity.
> When I press a key I am wasting energy for a very small amount of
> time when I am overcoming the weight (i.e. inertia) in the front of
> the key because it bends. There would be less wasteful bending and
> more dynamic range if there were less weight in front. Correct me if
> I'm wrong here, but I think the concept is as simple as that.  No need
> to fabricate a giant experimental contraption and write a multi-part
> journal article about it.

Well, you are correct that a key does bend, and the amount of bending is 
directly proportional to inertia and acceleration rate, but what of it? How 
does bending relate to "dynamic range" - whatever that is?

> Another aspect of this is time: the weight can change over the
> duration of the key press. This is why damper regulation can be
> important. But, again, a simple concept.
>
> I think a lot of us are confused about this stuff when we don't really
> need to be.  The hard part is figuring out how to engineer a key
> to behave at its best.

I'm confused about "dynamic range" and beyond that, I don't understand what 
it is I'm supposed to be confused about - I'm so confused!

Terry Farrell