First, watch this awesome slo-mo of a slinky being dropped.
Because it takes time for the tension to be released on the bottom of the slinky, it remains ‘held up’ while the top of the slinky falls. More subtly, the torsion is released faster than the tension and reaches the bottom first, uncoiling and rotating the bottom surface before the tension is released and the bottom finally begins to fall.
Social change behaves in a similar way. When a critical mass of thought or behavior changes state from OK to not-OK, it releases the social tension holding that thought or behavior in place. A wavefront of change moves through society from the change-point group outward to those most closely associated and onward from them in an expanding sphere of influence. The group farthest from the change point – either physically, socially or ideologically – is the last group to change.
The subtle part is that some part of that change may move faster. An idea, subordinate to, but foundational of the larger change may move through society first, followed later by large scale behavioral or ideological change. Examples might include the idea that tobacco smoking is unhealthy moving through society as a precursor to a later change that smoking is socially unacceptable, followed even later by policies and ideological reinforcement to discourage it. Another example being that information about stagnation in economic performance and high unemployment might move through society as a precursor to change in economic policy or even entire economic systems.
In the slinky, the inertia of the spring impedes the release of tension, which is why the bottom of the spring doesn’t fall at the same instant as the top. In society, not only does it take time for information to propagate, and for a critical mass of people to change opinion, but there is the additional impedance of disinformation, the inertia of entrenched interests hiding or distorting critical information in order to protect their power and income.
Finally, there is one other effect which is fascinating. Because the top of the slinky is released first, it the first thing to be affected by the change in state, therefore is the first thing to experience the acceleration of gravity. As a result, it actually outruns the tension-release propagating through the slinky, and reaches and passes the bottom of the slinky while it is still being held in place.
Again, this is mirrored in society. Those first to change have made large progress toward the new state of things before the last of the group has even begun to react. If they get far enough out front, they end up pulling the rest along even against their will. Revolutions can sweep through societies this way.