Key Leads and Inertia

[Bill Ballard]

At 6:00 AM -0400 6/13/03, Mark Davidson wrote:
>So far I like David's point best, that 85% of the energy goes into the
>hammer.  That means a 10% variation in key inertia becomes only
>a 1.5 variation in ....something.  Need more coffee.

Went to re-heat my coffee. Let me toss this in. Of the three main 
force in a piano action, friction, gravity and inertia, friction is 
the only opposing force which actually removes a significant portion 
of energy from the system. Both gravity and inertia store and return 
an appreciable amount of energy to the system on the return stroke. 
Lift the hammer up and when you remove your finger from the key, 
gravity is there to make the parts swing back down. With inertia, the 
extra force required in lifting a heavier hammer is stored as 
potential in the parts' angular momentum. When the stroke slams to an 
end, the rotational kinetic energy is transferred to the string (and 
the mass of felt fibers) and is promptly reflected/returned to the 
parts.

When energy is lost to friction, that energy is actually only 
converted to heat. In a piano action, we don't see a whole lot of 
thermal energy converted back into kinetic.

Bill Ballard RPT
NH Chapter, P.T.G.

"Out here on the food chain, you either          
    diet,die, or dine"
     ...........folksinger Mark Graham
+++++++++++++++++++++