Two objects with mass m[sub]1[/sub] and m[sub]2[/sub], connected with a spring (spring constant k).
You can drag the top one and compress it.
What is the minimum force (Fext) to bring the mass m[sub]1[/sub] jump up?
You can drag Fext to compress the spring,too!

If L0 is the original length of the spring.
The equilibrium poisition y[sub]1[/sub]=y[sub]2[/sub]+L0-m[sub]1[/sub]*g/k;
F1=m(d[sup]2[/sup]y[sub]1[/sub]/dy[sub]1[/sub][sup]2[/sup])= -k*(y1-y2-L0)-b*vy[sub]1[/sub];

Is it fun to play with it?

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