dmarkwick 261 Posted August 10, 2008 Can anyone save me a lot of shoeleather & describe, in a simplistic term, the relationship between Weight & Volume? Or, if necessary, the relationship between Weight, Volume & Rubbing? I know that Rubbing is how much the wind affects the particle's movement, so that's why I think the important relationship is between Weight & Volume. For my purposes I'm not interested in Rubbing at all. I'm trying to change a particle's Drop command so that each particle will follow exactly the same path as before, but slower. Obviously I'll be changing the XYZ velocity properties as well. Share this post Link to post Share on other sites
Gargantua 0 Posted August 10, 2008 Quote[/b] ]Weight & Volume it's about density and thus defines whether drop will fly in the sky or fall on the ground. rubbing defines if it's affected by wind or not Share this post Link to post Share on other sites
Maddmatt 1 Posted August 11, 2008 Increasing volume has the same effect as reducing weight. A particle with weight 10 and volume 7.9 should float perfectly in one spot if it has no initial velocity and rubbing. With these values the particle will never change it's initial vertical velocity unless maybe if rubbing is more than 0. I think rubbing doesn't only affect how much the particle is affected by wind, but it simulates air friction. So the particle will decelerate even when there is no wind. A very high rubbing value will just make the particle move with the wind. I might not be 100% correct, this is just based on past experience. Share this post Link to post Share on other sites
dmarkwick 261 Posted August 11, 2008 Well after going back to ColonelSanderLight's particle utility I guess there is some sort of relationship between Weight & Volume that is not well documented or known. You can balance Weight & Volume to give similar movements with different values (more Weight - less Volume) but that has a somewhat *slightly* different movement property. I think it's trying to simulate mass. But in any case, I think the labeling is mis-applied, certainly for weight. I mean, Newtonian physics says that weight is unimportant to how an object falls - it always must fall at the same rate. So saying that an object at 1kg falls slower than the same object at 10kg is wrong. Anyway, I managed to get a new balance where the particle I was interested in follows the same path it did before, but slower. I still don't understand what the Weight-Volume thing is supposed to simulate exactly, but using CSL particle utility gets me a working model. Share this post Link to post Share on other sites
Maddmatt 1 Posted August 12, 2008 But in any case, I think the labeling is mis-applied, certainly for weight. I mean, Newtonian physics says that weight is unimportant to how an object falls - it always must fall at the same rate. So saying that an object at 1kg falls slower than the same object at 10kg is wrong. But that is not taking into account the effect of air on the object. A feather isn't going to fall at the same rate as a ball, for example. If something is less dense than air (smoke maybe), then it's going to go up, not down. More weight helps 'fight' the air resistance. That's what the weight-volume thing is suppose to simulate Maybe it would have been easier if, instead of balancing weight and volume, we could just set the rate of vertical acceleration/deceleration. Share this post Link to post Share on other sites
dmarkwick 261 Posted August 12, 2008 But that is not taking into account the effect of air on the object.A feather isn't going to fall at the same rate as a ball, for example. That's why I was trying to get a feel for Weight & Volume without Rubbing. Take away Rubbing & you remove air friction right? This is why it's a little confusing to me. Share this post Link to post Share on other sites
Maddmatt 1 Posted August 13, 2008 But that is not taking into account the effect of air on the object.A feather isn't going to fall at the same rate as a ball, for example. That's why I was trying to get a feel for Weight & Volume without Rubbing. Take away Rubbing & you remove air friction right? This is why it's a little confusing to me. Weight and volume is to do with density. Less dense than air = float up. More dense = sink (think about how some things float or sink in water). Rubbing = wind and air friction. I'm no expert on this, just basing this on high school physics Share this post Link to post Share on other sites
dmarkwick 261 Posted August 13, 2008 Hmmm. Perhaps I'm still convinced though that anything with a positive Weight must fall down at a set rate, with no air friction (Rubbing = 0) Share this post Link to post Share on other sites
canukausiuka 1 Posted August 13, 2008 It would, except when you give it a volume, then the engine also calculates its buoyancy. So if you are less dense than air, your particle will go up. If you are more dense than air, it will drop. And if you set it to the density of air (which in-game is close to, but not quite the actual density in kg/m^3). Rubbing sets the particle's friction with the air, which can cause a few effects. High rubbing particles will very quickly accelerate/decelerate towards the speed of the air. Low rubbing takes a long time to move towards the air speed. And no rubbing means that there is no maximum speed, and that the particle is not affected by wind. I've always assumed I was entering mass (in kg), volume (in m^3), and then I would experiment with rubbing. Share this post Link to post Share on other sites
