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Re: operational F, m, and a (velocity measurements with fish-scal es)



At 03:28 PM 10/19/01 -0500, RAUBER, JOEL wrote:
I agree that if
the spring scale is in a state of uniform motion relative to an inertial
reference frame, that looking at a snapshot picture and obtaining x, is
sufficient for determining the value of the spring force on the object its
attached to at that instant of time.

Well, of course. That's what scales are for.

But that seems to me as tantamount to
saying I can use the spring scale to determine the force that the spring
scale exerts on an object. I have no arguement with that.

Then we're in complete agreement. That's what scales are for. That's the
whole point.

But that's not why I thought spring scales were brought into the
conversation in the first place. I thought they were brought into the
discussion for purposes of using them operationally to determine other
unknown forces without acceleration measurements.

Huh? What other forces? What unknown forces? How could a scale measure a
force other than the force on the object it's connected to? We're not
talking about telekinesis here.

The last three words worry me "without acceleration measurements". The
spring scale does a fine job of measuring a force in the absence of
acceleration, for instance in the scale+scale+chassis system I diagrammed
earlier.