"Bob Engelhardt" wrote in message
...
Let's say there's a lever with 3 forces acting on it:

1 2 3
V_________________________V____________V
/\

let F1, F2, & F3 be the forces and L1, L2, & L3 be the distances of
those forces from the fulcrum.

Then
F1*L1 = F2*L2 + F3*L3

Simple enough. Now, let's say that F1 is a fixed force (e.g., a
weight sitting on the lever). Then F2 & F3 could be any combination
of forces, as long as it balances.

Now say that points 2 & 3 are fixed. I.e., the lever is "tied down"
at those points. What are the forces acting on those tie downs? Is
the torque (moment of inertia, if you will) attributable to each
equal, so that the forces are inversely proportional to the
distances? I.e.:
F2*L2 = F3*L3 (= 1/2 F1*L1)

It seems intuitively so, but if it is, how do you show that it is?

This has been bugging me for days, so any resolution that you can
offer will be greatly appreciated.

Bob

A real beam will bend between F1 and F2, and pull away from F3.

http://en.wikipedia.org/wiki/Statically_indeterminate

jsw