Bug / Crash Rope is moving wen increasing his length

[josemendez]

Unfortunately in my case the rope is blowing up... That's why I try to make a simple example with a free rope floating in the air which showed the unrealistic behavior that I described above. But, thanks to your answer, I understand this behavior.

It's unrealistic, but unfortunately the only way to "fix" it would be to use a true continuum model of the rope (where mass and volume are completely tied to each other = constant density, and bend/stretch deformations are coupled) which means ditching particle-based solutions entirely and using FEM or something akin. As far as I know, no existing realtime physics engine does this.

By the way, my "real case" is a rope which is attached to a boat and floating in sea (I made a system which compute buoyancy and drag force against the wave for each particles).
Do you think that increasing the rope from the boat should change the moment little enough to prevent this kind of behaviour ?

If the rope is attached to a boat and floating around under drag forces, this should work ok.

Here's the results I get with a rope that's attached at one end, zero gravity and mild isotropic drag (damping). As you can see the momentum gain is redistributed along the entire rope, which makes it flutter a bit as it grows (doesn't grow in a straight line) but otherwise it works well: