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How to mask drag force by vel?

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Hi there, :D 
I have just started to learn houdini, so, hope you don't mind if the question is too lower level =]

I'm doing a little test, trying to simulate throwing an icecream ball onto something.
The problem here right now, is after I added a drag force node, all the particles are froze in the air...
I only want the particles which collide with the surface to be froze. 
So, I'm wondering how could I check the per particle's velocity as a condition to apply it on the drag foce?
I hope I explained the problem well. The file is attached below.


Thanks a lot if any body can give any kinds of suggestions.  :lol:



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Hi all, I find some thing from previous post.

One is from here:



using a group node to separate particles by velocity

length($VX, $VY, $VZ) < 0.1

and using a 'pop force' node doing something like this.

//groups created in SOPs.

if(@group_red == 1)
    //set total force to force*0.2 for redGRP
    force *= 0.2;

if(@group_green == 1)
    //set noise amplitude amp+10 for greenGRP
    amp += 10;

but here is another problem, when I mid-click any node in the dopnetwork ( the flipsolver node, merge node or source volume node), none of them has velocity attribute, even position attribute or id attribute...so how could I bring the velocity inhere???


Thanks a lot~~~ =]

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just find the solution by accident.
It's simpler than I thought. 
the easier way is to use old pop solver, which can create drag force in it
But for houdini 13 and 14, plug a 'pop group' node to the 'Sourcing' input of flip solver,
and under the combine tab,  fill the group name in the Group bar, select Equals mode, then fill in something like : @viscosity>xxxx.(I use viscosity as test).
what confusing me before was the 'Rule' tab, I thought I need to type the vex expression there, something like @viscosity >  XXX, but it's not working...
Hope I could figure out how to use the 'Rule' things by another accident~ 


the file is attached below, no fancy stuff, but takes me a lot of time to figure out...=.=|||




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