Re: Force sensors (2)

["Rauber, Joel Phys" <RAUBERJ@mg.sdstate.edu>]

> Rauber, Joel              Phys says:
>
> > 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.

> Actually, you must measure the spring elongation to be constant over time.
> This does mean that the acceleration is zero,

And hence is measuring the acceleration, i.e. this is how you operationally 
use the apparatus.  You look for the necessary condition that the 
acceleration is zero.

> but the converse doesn't
> work: acceleration = 0 is not sufficient to conclude that equilibrium has
> been reached.

> The velocity, jerk, ... must also be zero.

The velocity does not have to be zero for the system to be in equilibrium.

The jerk and higher order derivatives I assume, I'll have to think about 
that for a while.  You may have just put your finger on why thinking of N2 
as an operational definition of force by relating it to acceleration is not 
the same as saying kinematics is the same as dynamics.  Comments on this 
thought anyone??

> Not to mention that I think everyone else in this discussion is refering to
> measuring the acceleration which is related to the force by N1.  It's not
> clear why discussion of internal accelerations is helpful here.

An internal acceleration is an acceleration, and my comment was that the use 
of the spring scale to measure a force works by really measuring an 
acceleration first, then we can infer the force.  This is why the internal 
acceleration is important to my point.

Joel Rauber

PS
Thjs is fun!!