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Re: Spring Problem Revisited

At 11:42 AM 10/30/97 -0500, you wrote:
Good answers guys, I'm starting to see the light! But, I'm still
bothered by something. Let me restate the problem another way.
We have a horizontal, unstretched, Hookean spring connected at one end
to a rigid support. At the other end, I attach a mass m resting on a
frictionless surface. Now, I pull to the right on MASS m (not on the spring
itself) with force F=kx. The spring pulls back to the left on the MASS m
(not
on me) with force F=-kx. Now, the sum of the horizontal forces acting ON THE
MASS is 0. NOW, how can the MASS (not the spring itself) ever accelerate?
By the way, Donald Simanek came close to answering this in his post,
but I'm wondering if anyone else has any insight.

As you describe it here, the mass will not accelerate since there is no net
force. If your applied force is constantly adjusted to match the spring's
restoring force the mass moves at constant velocity.

Assume for a moment that you start the system at its equilibrium position
(x=0) at zero velocity. The spring exerts zero force. You exert zero
force. The mass remains at rest. However, any incremental force dF other
than zero will cause the block to move because it is then unbalanced. If
the applied force always remains larger than the spring's restoring force
by this increment dF the mass will accelerate with a = dF/m



George Spagna **********************************************
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