Help Force Zone apply different accelaration to 2 ropes

[josemendez]

As an update: Considering it's difficult to achieve this (no matter whether I use acceleration or force mode, I cannot use 2 different force values to apply force on 2 ropes, which may make the bouyancy simulation unreal) ,

I'm not entirely sure what your use case is, sorry. Force zones already support affecting each actor/particle differently, by using force mode.

It's also how it works in the real world. Take buoyancy, for instance: buoyant force acting on a completely submerged object only depends on the density ratio of the object and the liquid it's submerged in.

The density of the liquid (and all its other properties) is the same for all submerged objects, so the only remaining variable is the density of each object: buoyant force = fluidDensity * objectVolume * -gravity. Since acceleration = force / mass, you end up with acceleration = fluidDensity / objectDensity * -gravity. Since fluid density and gravity are constants, you can treat the density ratio as a single variable defined per object that you can control by altering the object's mass.

So following this, you can set the mass of each of your actors differently (accounting for their volume as well, in case you want) and it will somewhat accurately simulate buoyancy, resulting in the same accelerations you'd get from different force values for each actor/force zone combination.

This way, I can calculate the acceleration based on the density ratio of the material to water. If I use force mode, I need to calculate the volume of the line in water, which is a bit difficult

You can use the force zone's falloff to approximate the submerged volume using the distance of each particle to the surface. For instance if you set max falloff distance to the diameter of the line, you'll get maximum buoyancy when the line is completely submerged, and it will linearly decay to zero as the line goes above the water surface.

In any case, the fishing line is so thin and its volume so small I doubt this will have any impact on its behavior.

I hope this feature (1 force zone, different force val/direction for different actors) can be supported in future version.

If you mean support for manually specifying an arbitrary force for each actor that may go inside a force zone, that would be pretty impractical from a UX perspective as it would force you to specify a force value for every possible force zone/actor combination in the scene. This is the same reason why most existing physics engines don't specify a friction coefficient for each possible combination of materials (which would be the physically accurate thing to do), and instead give each material its own friction coefficient.

Still, note you can write your own force zones that affect particles in any way you want. There's an example of this (a gravity well) in the manual: https://obi.virtualmethodstudio.com/manu...icles.html

kind regards,