hammer velocity

[Mike Spalding]

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Ric,

A conceptual tool that helps us visualize this problem is the "free body =
diagram".  Draw a hammer and shank, then draw an arrow for each force =
acting on the hammer:  gravity, jack, rep. lever, center pin, string.  =
period.  Between let-off and impact, the jack, rep lever, and string are =
not in contact with the knuckle.  The list of forces acting on the =
hammer/shank assembly consists of gravity and center pin.  period.  Both =
are acting to decelerate the hammer.

keystroke before let-off, and rebound after impact, are more complicated =
because there are more forces involved, and they are not all acting in =
the same direction, but the method would be the same.

hope this helps,

Mike Spalding RPT


  ----- Original Message -----=20
  From: Richard Brekne=20
  To: Kevin E. Ramsey ; Pianotech=20
  Sent: Sunday, April 27, 2003 5:25 AM
  Subject: Re: hammer velocity


   =20
  "Kevin E. Ramsey" wrote:=20

    Richard BrekneI believe there is a letoff position (just under 1mm) =
that is so close that the hammer does not have a chance to start =
de-acceleration. I havent gotten into all this side of things very much =
yet, so I am not sure of myself here, but isnt there some sort of "left =
over" force that keeps an object in acceleration for some small period =
of time even tho the origional applied force is removed ?  Like a bullet =
coming out of a rifle ?? Doesnt that meet its maximum acceleration some =
few milliseconds after the explosion of the shell ? RicB     No, =
Richard, no "left over" force is there to continue accelerating an =
object after it's direct influence is removed. If you really want to =
know what happens inside a rifle, feel free to write me privately. No, =
the bullet doesn't continue accelerating after leaving the barrel.  The =
only thing that I think could possibly continue accelerating a hammer =
after the jack has tripped would perhaps be the flex of the shank =
becoming straight again, but at 1 mm, I'm not sure that it could be =
measured without high-speed cameras to capture the action.    In =
reality, the pianist has the skill to adapt to the instrument, and still =
make music.  All we can do is to provide them with the best regulated =
and voiced instrument we can, and they can take it from there, if they =
are truely "musicians".Kevin.

  Well like I say guys... I havent brushed up my inertia physics in a =
long time :) Another fellow (who knows I like Star Trek series) wrote =
privatly to me as asked me if I'd ever seen the episode where the =
Enterprise does a saucer seperation... and he aske me "now is the saucer =
accelerating away from the ship, or is the ship just slowing down =
faster"... I kinda got the point :)=20

  Still, there does seem to be some pent up force in the entire system =
that is throwing the hammer upwards. Key and shank flex are two that get =
mentioned a bit in this connection. Seems to me that all this is the =
direct result of the amount of force put on the keyfront. Just where and =
how this pent up energy gets released I am unsure of. Within the space =
of 1mm  of key travel perhaps ?=20

  btw... the rifle thing... I dont think I mentioned anything about =
after leaving the barrel... did I ? I think I said quite clearly after =
the initial explosion.=20

  Cheers=20

  --=20
  Richard Brekne=20
  RPT, N.P.T.F.=20
  UiB, Bergen, Norway=20
  mailto:rbrekne@broadpark.no=20
  http://home.broadpark.no/~rbrekne/ricmain.html=20
   =20

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