<!doctype html public "-//w3c//dtd html 4.0 transitional//en"> <html> <body bgcolor="#FFFFFF" style="FONT-SIZE: 14pt; FONT-FAMILY: Arial; BACKGROUND-COLOR: #ffffff">   "Don A. Gilmore" wrote: <blockquote TYPE=CITE><style></style> Hi guys: Before you all get too carried away, here is some food for thought. First of all, forget about momentum.  Momentum (and, once again, we need to think in terms of angular momentum) is moment of inertia x angular velocity and is in units of slug-ft^2/sec or kg-m^2/s.  It is really only useful in calculating elastic collisions between objects (like billiard balls, for example) that exhibit "conservation of momentum", or impulse calculations.  Impulse is only useful if we are worried about constant forces, etc.  You were all doing just fine with kinetic energy. Since the hammer is free from any outside influence between the time it is released by the action and the time it strikes the string, we are talking about two totally independent things: how the action gets it up to speed and what happens when it strikes the string.</blockquote> The origional concern of this was to compare the touchweight characteristics of  various methods of counterbalancing, primarilly lead vs springs. We were looking (compaitively) at two related issues really... the << heavyness >> (which we evidently still havent really defined in terms of physics) of the mass being moved at all possible (reasonable) speeds, and whether or not there exists some << ideal >> amount or range  of key inertia for top action inertia for any given overall action ratio (defined in terms of the Balance Weight Ratio commonly called the Strike Weight Ratio.) i.e... how the action gets up to speed and what the amount and character of the work the fingers need to do to accomplish that. I find all the rest of it very interesting... but personally I want to iron this (above) bit out once and for all... at least in my own head. My own confusions relating to some of this surround largely the term inertia. On the one hand I have been corrected just these past days by Sarah, Mark, and a few others and have been told that inertia = mass. But just today I get the following in the mail from a long time contributer who has a reputation about him for being a physics guy. <blockquote> "Inertia is directly proportional to mass, but proportional the the square of the velocity."</blockquote> Other places on the net seem pretty clearly to equate inertia with the equation  F = ma. Not strange at all that I was mixing momentum up with inertia. Obviously both these definitions cant be true. So which is it going to be folks ?     -- Richard Brekne RPT, N.P.T.F. UiB, Bergen, Norway <A HREF="mailto:rbrekne@broadpark.no">mailto:rbrekne@broadpark.no</A> <A HREF="http://home.broadpark.no/~rbrekne/ricmain.html">http://home.broadpark.no/~rbrekne/ricmain.html</A> <A HREF="http://www.hf.uib.no/grieg/personer/cv_RB.html">http://www.hf.uib.no/grieg/personer/cv_RB.html</A>   </body> </html>