RE Friction

[Dan Squire]

>Ken Sloane wrote:

>The laws of nature do not change from one system to another. However, our
>methods of analysis with pianos sometimes introduce conditions into that
>analysis that do not exist when the piano is being played as a musical
>instrument. For example, when we use touch weights to measure friction in an
>action, the key moves slowly and the knuckle stays, more or less, continuously
>in contact with the jack and repetition lever. This is also true with the
>wippen/capstan bearing.  I believe that it is generally considered that this
>does not occur when the piano is played. After initial compression of the
>knuckle against the jack/rep lever and the capstan against the wip bearing,
>the hammer assembly gets moving. The inertia of the moving hammer assembly
>then helps to carry the assembly to the string. So, is there more friction
>during that "period of compression" (as opposed to when we use touch weights)
>and less when the inertia "takes over"? Even more confusing is how the hell we
>would begin to measure these "varying" friction levels when playing.
>

No problem.  First get information on the acceleration.
Then do a combined static- and inertia-force analysis.

Dan Squire
University of Houston