[CAUT] Digest, Vol 1103, Issue 85 Moving Wippen Rail

[Richard Brekne]

A good observation. I think tho if you think about it, the balance scale 
has platforms that swing freely. Not only to they tilt if a weight is 
put in them off senter but they swing in or outwards so that the cables, 
wires, whathave you that suspend them from the balance arm find the 
appropriate angle off vertical so as to compensate.  The vertical 
component of weight stays the same because the effective length of the 
arm has changed.

Actually this is kind of cool you mention as I had this long discussion 
with Mark Davidson a while back... who has a physics degree and knows 
this stuff pretty well. He thinks in terms of torque when dealing with 
levers.  My more limited education points me in the direction of 
thinking of the effective length of arms... i.e. translating everything 
in terms of vertical and horizontal force vectors.  As it turns out you 
can actually describe the ratio of a lever at any point in its motion 
both ways.  But its a bit cumbersome to do it my way for ever mm of a 
levers field of motion.

Still.. your balance scale perfectly shows exactly why I think we have 
to admit your position about the jack angle being important as wrong.  
On the other hand...  You did point out that the jack center position is 
also important.  One can find the vertical component... and there by the 
momentary ratio of the leverage at any point by simply drawing a right 
triangle from the position of load input/output to the point of support 
on the lever with the line opposite of the line between these two being 
vertical. A horizontal line from the flange center out to this line then 
is the distance of the arm with the lever in whatever position its in.

Cheers
RicB


    A question back to you. A balance type scale. It has a platform 4 inches
    across. the weight doesn't change due to where you put the load on the
    platform. It is still transfered back to the point on the lever that the
    platform is attached. According to you if we move the load farther
    from the
    fulcrum the weight should change. The design of the intermediary
    device has
    a lot to do with it I think.

    Keith