Key Leads and Inertia

[Richard Brekne]

Hi Sarah, and others. Back from a weekend in the hills and busy getting caught
up with P-tech mail. A couple comments below.

Sarah Fox wrote:

> Hi Ric,
>
> Cool applet! :-)  Anyone using it should be aware that the rotating platform
> has mass, else the acceleration of the hanging mass (whatever amount of
> mass) would be 9.8 m/s^2 with the platform unloaded.  Also, be aware that
> the amount of hanging mass is not equivalent to tangential force, but the
> two are of course related -- the best approximation occurring when the least
> weight is used and the acceleration is the least (i.e. and farthest from the
> asymptote of 9.8 m/s^2).  Anyway, yes, the applet applies perfectly to the
> touchweight issue.

Grin... glad you liked it. And thanks for the clarifications.

>
> >From a static, touchweight perspective, 500 g on the outer perimeter is
> equivalent to 1000 g mid-way out on the platform (half the radius).
> However, from the perspective of dynamic performance, the 1000 g solution
> yields a lower moment of inertia (by half, ignoring the unknown moment of
> inertia of the supporting platform) and is therefore capable of greater
> rotational acceleration with the same tangential force (similar to finger
> pressing down on end of key).  (Of course we can't see the full magnitude of
> the effect, since the platform has unknown mass.  To minimize the
> contribution of the platform, place lots of mass on the platform.)

Yes... thats sort of how I read the results, tho its going to take me a bit to
weed through the refered too maths that explain the moment of interia as
described by this site. So let me see if I understand this correctly. Ignoring
the moment of inertia for the key, this is shows that for a given FW
specification, more leads placed closer to the balance rail pin yeild a lower
moment of inertia, and yield greater degrees of acceleration then less lead out
towards the end of the key. Yes ?

This being the case... then loweing key inertia, and hence increasing key
acceleration can be accomplished by concentrating more of whatever key mass is
used in the center.. yes again ?  If so... what happens to half the argumenation
against the accelerated action ?

> Thanks for pointing us to this cool virtual demonstration!
>
> Peace,
> Sarah

Cheers

RicB

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