Paricles - different mass? or two gravity streams?

[cwalrus]

stumped!

 

I want some of my particles to have less mass than others. I've tried several things:

 

1- duplicating the gravity way upstream and changing it per stream. Doesn't work - gravity doesn't like to be above the Solver?

 

2 - creating a POPGroup called "MyParts", then trying to access it via the gravity node's "Group" option.  Can't seem to access the group - it's not in the gravity's Group selection menu.

 

3- create mass. Um.  How the bleep do you do that???

 

 

Any tips?

 

THanks!

 

 

[fathom]

you using a pop force node or a gravity node?  pop force might be more flexible.  for example, it goes above the solver.  it also has vex expressions to adjust the values per particle.

[cwalrus]

Well i figured out mass sort of- simply add a POP Property node and check it...... Then of course I have a mass slider, but changing that doesn't seem to affect the particles. 

 

I've been assuming that a POP stream is isolated to the actual network 'stream' on which you are working, but now after reading some posts I think that I have to set up a "POP Stream" to separately affect the... streams. 

How do I specify in a POPStream node to access only the particles that have been replicated, or only the particles piped into their input? I want to have access to both the originals, and the replicated ones...

 

thanks for info!

[Guest tar]

Seems like you're missing that mass is never affected by gravity... so you need to uncheck 'Ignore Mass' on a Pop Force node

[cwalrus]

hmmm - but look at what the Docs say:

 

The Gravity Force DOP applies forces on objects as if they were inside a gravity field. The amount of force is proportional to the object’s mass. If an object has twice the mass, it receives twice the force.

 

 

Basically all I want is for some of them to fall fast and hard, like stones, and others to fall more slowly, like feathers. 

[Guest tar]

Just create two gravity nodes and two popobjects, point each Gravity's Group to a popobject and set different Forces.  There are better ways but this will work for now.

 

BTW. Best to use the manuals as a guideline - it's works best to extrapolate it out. 

[anim]

hmmm - but look at what the Docs say:

 

The Gravity Force DOP applies forces on objects as if they were inside a gravity field. The amount of force is proportional to the object’s mass. If an object has twice the mass, it receives twice the force.

 

 

Basically all I want is for some of them to fall fast and hard, like stones, and others to fall more slowly, like feathers. 

that means in other words that the resulting acceleration will be the same regardless of the mass and not different as you expect

since

F = m*a

and if Gravity is force proportional to mass then: F = G*m

then

G*m = m*a

therefore G = a

so whatever you set as your gravity will be acceleration of your particle regargless of the mass

but to your actual problem:

- just do 1 stream

- vary mass using POP property with some VEXpression or wrangle or ...

- add POP Drag to simulate air resistance

- uncheck Ignore Mass on POP Drag, this will make heavy some objects fall faster than light ones

- use POP Force with Ignore Mass on as proper gravity OR use Gravity Force DOP as you do now

- play with Air Resistance on POP Drag

[cwalrus]

thanks guys