What's all this I hear about Inertia ?

[William Monroe]

David B. Stang wrote:

SNIP

> 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.

Interesting idea David,

I think you'll get some corrective responses, however.  If you had a 1000kg key and tried to play it ff  you would break a finger or two - easily - regardless of downweight specs.  Why?  Inertia is huge in the 1000kg key.  By your definition of mass = inertia, I'd think you would have noticed this.  Very little inertia in a standard key, relative to the 1000kg key, no?  Thus, massive performance differences, well beyond dynamic range.

Imagine a 1000kg steel I-Beam, perfectly balanced on a fulcrum.  Downweight would be < one gram.  Try to punch it down.  Then maybe put your foot under one end, and accelerate it to a high velocity and see how your toes make out.  You could do these experiments with a standard key too,  just for anecdotal comparison, but I don't think you need to.  In the case of the beam, your hand and foot will be broken.  I doubt you would suffer any such trauma with the standard key.  

I think you'll be hard pressed to find a piano technician or physicist that would agree that the inertia in a 500kg key = that of a 50g key for example.  Note the difference in mass, and, inertia.

 
David also wrote:
SNIP:

>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.

Nothing could be more false.  Things are not as simple as you've suggested.  I hope this doesn't come across poorly, but there are some very important misconceptions in your post, David.

William R. Monroe


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