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Re: Force sensors (2)



I don't have to measure the acceleration to use the scale. It can be in an
accelerating frame (the ubiquitous bathroom scale in the accelerating
elevator) and will still measure the force on the object being 'weighed'.
IF and only if I know the true weight of the object can the scale be used
as an accelerometer. Otherwise, I simply read off the force.

OK--to get the 'true' weight I do have to know the acceleration is zero,
but again, without knowing the true weight ahead of time, the scale does
not in and of itself measure an acceleration.

If you mean just being sure the object is at rest relative to the spring
scale (1) below, then yes, that's a stretch to say you are measuring
acceleration.

Rick
----------
From: Rauber, Joel

b) Do you really think its stretching the point. When you use a spring
scale to measure a force the procedure is as follows:

1) You put the spring in equilibrium. This is the step where you measure

the acceleration. You must measure the acceleration to be zero in order
to
know that the spring is in equilibrium.

2) Once its in equilibrium then you measure the elongation of the spring
and
read the force off the scale.

Before you read the force you had to measure the acceleration. And its
in
this sense that I mean that the device really works by measuring
accleration. I think that this is how we basically make all measurements
of
force, by first measuring accelerations and then making inferences. (for

the moment lets confine the discussion to spring scales as force sensors,

and then later talk about other force sensors; I want to establish
agreement
or disagreement with what I say above).

Joel