force relative to mass, incorrect behaviour.

[super gnu]

many particles of different sizes. 

ive applied a mass operator, set to mass by volume. 

passed on to a force operator with "relative to mass" enabled. 


two things.. 

one:  the smaller particles are heaver (judging by  the result of the force operator)  than the big ones.   enabling "invert" on the mass operator fixes this, but seems incorrect behaviour as a default. 

two, when i add wind, the heavier particles are affected more than the light ones... this is the opposite of correct behaviour.      heavier particles should be affected more by gravity and less by wind. 


i can forsee situations where a larger particle could catch more wind, if you are using the mass property as a standin for size.  and therefore maybe an "invert behaviour for wind"  style tickbox might be useful, so you can have either behaviour. 

i have a deadline in a week or so, and need this correct behaviour... any workaround or possibility of a fix? 

thanks all.

[insertmesh]

Don´t have a solution for this, just a random idea, if you haven´t tried already: Put a slow op on top. That sometimes fixes unexpected behaviour (if its not a bug), where different forces are counteracting each other (maybe physx collisions vs wind, no idea what your exact setup is).
Worth a shot, since tySon is out of town...

[super gnu]

thanks for the reply.. i dont think a slow operator will help. i just need larger particles to fall faster, but smaller particles to be affected by wind more... maybe i can set up the gravity in one force operator, then invert the mass and pass to a second force operator for the wind.. need to see if that will work.

[tyFlow]

Mass affect in tyFlow works as intended. The algorithm is simple: acceleration = force * 1/mass, which is typical for simulation software. Note that given that algorithm, particles with less mass will travel faster than those with more mass when pushed by forces like wind, which is what you'd expect in nature - objects with more mass are subject to more inertia.

That said, the force of gravity, in nature, does not discriminate based on mass. Heavier objects fall at the same speed as lighter objects. The mistake might be assuming that heavier objects would fall faster.