> See it a different way - you say you have a system simulating something
> having next to nothing to do with real physics and now you want the
> *correct* formula to calculate a certain effect in this system.  What
> several people gave you was the formula for conservation of total system
> energy which would be the point to start with when you do a *realistic*
> simulation.  Now this naturally does not help you because you don't care
> about the energy in your system but it should be obvious that your
> question does not make much sense then - there is no correct formula.

It does have to do with physics. I add gravity, wind etc and use formulae to
calculate velocity etc. Like: when an object falls 10 meters with some
initial velocity and heading, it will have [insert correct value here]
velocity in [insert correct direction] direction afterwards. Those are
physical properties that I do try to achieve.
Now, how to go about implementing it? It's not a real physical system, but
merely some particle system with some physical properties. What I want is to
include certain characteristics which will in turn result in realistic kinds
of animation. Look at Rune's or my other particle system, they do have
certain characteristics which have their basis in the real world.

Then the formula for a 100% realistic simulation would be helpful if, in
fact, certain criteria are present in my system. Some of them are, some
aren't. There is energy in my system, but its just stuck with the particles.
When a particle hits the floor, I don't add energy to the floor, calculate
its... Ehm, forget the right term. "Laziness in getting moved" I'll entitle
it :-) and thus reduce the energy remaining for the particle, I just
subtract some percentage of the velocity which is parallel to the surface
normal.

Take, for example, the distance an object has dropped in free fall, the
formula is
h = g*t^2 / 2
There's nothing like air stopping the falling in this formula, it's entirely
simplified, but still relevant. It just assumes that there's no friction. I
was asking for the same: in a no friction-system, what's the rate of
slowdown for an object moving uphill?

As said before: the points discussed are valid, but they weren't what I was
asking for. I didn't want to discuss how and why my particle system works
the way it does, I've spent thought on that already and decided to go a
certain way. The discussion provided me with some insight into some
drawbacks of the approach, but they weren't relevant to the question.

> You should understand that most people here when talking about gravity,
> energy etc. are referring to what these terms mean in physics, not how
> you use them in your simulation system.  In physics gravity in an
> acceleration which - according to Newton - exerts a force on all masses
> in the system.  Whether or not this results in a change of velocity (and
> thereby in kinetic energy) depends on the environment.

Of course, I understand that. Still, I was trying to find a solution to a
problem that occurs *in* my simulation, not *in* the real world. While I was
describing what happens in the system and trying to find a solution for
that, I got responses like "oscillation doesn't happen in the real world".
How does that help me solve my problem? And, aside of that, I'm not a newbie
to the real world. :-)

I hope there are no hurt feelings because of my recent reply. I just felt at
some point like it was a discussion of "real world" vs "simulation" and that
wasn't really an issue, real world just is real, simulation isn't, see? ;-)

Regards,
Tim

-- 
"Tim Nikias v2.0"
Homepage: <http://www.nolights.de>
Email: tim.nikias (@) nolights.de

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