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Re: RE BALANCE PROBLEM

David Abineri wrote:

What is wrong with the argument that says that any force applied at A is 'felt' by the balance at C, thus creating a clockwise torque?

Thanks, David Abineri

I don't know if this diagram will come through but, if AB is a rigid
beam attached to a rigid post BC which is attached to a rigid beam CD
which is pivoted about the marked pivot point, what happens as an
increasing vertical downward force is applied at A? Which way does the
balance tip? What is a good, instructive, way to look at this
situation? Am I making this more complicated that it is?

Thanks for any help, David Abineri

A B
_____________________________________
|
|
|
D _____________________________| C
/\

--
David Abineri
dabineri@choice.net



--
David Abineri
dabineri@choice.net

I can see where you would want to have the downward force at A applied to the lower bar at a point near C, implying that the system might
tilt clockwise. That applied force, however, also produces a large torque about point B - and this will be transferred to the lower bar
through the vertical connecting rod. In net, these result in the same torque as the applied force produces about the fulcrum - so the
system tilts counterclockwise.

A less confusing approach is to simply look at the torques. It's difficult to tell from your diagram, but I assume the system is in
balance before the force is applied at A - therefore no net initial torque about the fulcrum. The downward force at A has a
counterclockwise torque about the fulcrum, therefore the system tips counterclockwise. Looking at the internal forces along BC is futile
because they don't produce net torque (these internal forces cancel.)

Bob at PC