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Documentation : Effex : Objects : Operators

### POP::Surface Tension

Node Params Constraints
POP::Surface Tension

Surface tension is only of importance in small scale scenarios of liquids (droplets wobbling) but can create more realistic and interesting behaviors such as breaking up of sheets due to surface tension (it's quite the opposite of the thin sheet algorithm).
The theory of surface tension is quite simple: liquid particles feel attracted to other liquid particles.
The problem remains a challenging task though.
The surface tension node is an SPH technique (while the liquid simulations in Effex is using FLIP) and has been adapted to work with FLIP.
It contains two different algorithms, one is the famous surface tension model by Müller et al 2003 and the other is the cohesion model by Techner et al 2011 (and is state-of-the-art).
Both have a time step restriction which means that enough substeps must be used (or an accordingly low time step) in order for the algorithm to remain stable though in the end they are just forces (only a special force in this case, that's why it is an operator).
The following nodes are either required or optional:
1. Surface Properties node (required in Surface Properties mode. Not required in Cohesion mode)
2. Volume Properties node (optional but can speed up the calculations tremendously. Not really required in Cohesion mode as all particles can be used)