1. + and - Stability/ Unstability -Repulsion
Like charges (repulsive force):
and the equilibrium point is always STABLE.
i.e. fluctuation to left (x<5) and +ve force pushes to right (toward x=5), conversely
fluctuation to right (x>5) and -ve force pushes to left (toward x=5).
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2. + and - Stability/ Unstability -Attraction
Unlike charges (attractive force):
and the equilibrium point is not always STABLE.
For too weak a spring (upper) fluctuation to left (x<5) and -ve force pushes to left AWAY from the force balance point –UNSTABLE.
For a stronger spring (lower) fluctuation to left (x<5) and +ve force pushes to right toward the force balance point –STABLE.