The effect from the images does not look good so I did not use it.
[s]This is my first version without the 3rd graph.[/s]
A spring is added at the center, user can drag object (at the bottom) to the end of the spring -- the object will attach to the spring automatically. The spring will reach new equilibrium shortly.

Drag the "hand" in the simulation downward with mouse , then release the mouse.

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Download EJS jar file(1352.5kB):double click downloaded file to run it. (22 times by 11 users) , Download EJS source (3 times by 2 users) View EJS source