Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: Spring Problem Revisited One Last Time



Much thanks to all who responded to my Spring Problem questions last
week. I'm beginning to see the light! With one more push in the right
direction, I might have this thing figured out. I'm like a vulture hovering
over this problem, ever circling, eventually diving in for the kill. However,
there is still one concept holding me back. If I can get this last point
figured out, I think I may have it.
Let's say we have a horizontal, massless, Hookean spring (k=2N/m)
attached at its left end to a rigid support. Let's say I pull with a CONSTANT
6N force to the right. The spring stretches out to position x=3m and comes to
rest, correct? Now, my question is in regard to the spring force which is
acting back toward the left as I exert my force to the right. Does it also
equal 6N in magnitude as the 3rd law would suggest, or does it vary from 0 to
-6N as F=-kx would suggest?
Any light that anyone could shed on this question will be greatly
appreciated.

If there is no mass involved you will be unable to exert a 6-N force
on the end of the spring. That end may be considered to be a massless
particle which, to remain at finite acceleration, must have zero net
force acting upon it. The hypothesis "Let's say I pull with a CONSTANT
6N force to the right" is incapable of execution. Even the premises of
Gedanken experiments are constrained by the laws of physics.

Leigh