[ODE] problem with adding forces

[Adam Paul Coates]

Clarification (and this is of general importance when dealing with any
graphics/physics stuff):  you can use whatever units you'd like as long as
you're consistent.  A Newton is the SI unit for kg*m/s/s, so if you're
using meters/kilograms, etc. for your units, then this works fine.  On the
other hand, I'm an aviation guy, so I tend to have data in slugs/pounds:
1 Pound = 1 slug*ft/s/s.  Similarly, you can use any coordinate frame
you'd like.  In my worlds I use North-East-Down as my x/y/z axes (again,
aeronautics) but you can just as well choose whatever is easiest for you
to work with.  All ODE sees is numbers and the basic relationships that
Martin and Cyril pointed out.  F = ma is true no matter what unit standard
you use or coordinate frame.

I don't think that will help your specific problem, but I hope it helps
point your mind in the right direction :)

Best,
Adam C.

On Thu, 7 Aug 2003, Cyril Labordrie wrote:

> There is a lot of questions !!
>
> All units must be un International Units System
>
> As Martin Said
>
> F = m a
>
> F is the Force in Newton, Newton is equivalent to ML/T*T.
>
> a = dv / dt
>
> and v = d Pos / dt
>
>
> to answer to your question, it depends on the mass of your body
>
> If you consider a small timestep for exemple 1 sec, DT = 1s it is easier
> to give you an idea.
>
> DPos  = Dv * 1
> 	= Da * 1
>
> then DPos = F / m
>
> if M is Greater than F it is normal it does not move.
>
> Cyril
>
>
>
>
>
> -----Message d'origine-----
> De : ode-admin@q12.org [mailto:ode-admin@q12.org] De la part de Martin
> C. Martin
> Envoyé : jeudi 7 août 2003 00:31
> À : lazareer
> Cc : ode@q12.org
> Objet : Re: [ODE] problem with adding forces
>
> F = m a
>
> - Martin
>
> lazareer wrote:
> >
> > Wednesday, August 6, 2003, 10:11:08 PM, lazareer wrote:
> >
> > l>> I am new on this list, and maybe my question is silly and
> > l>> the answer is obvious but I will ask it anyway:
> > l>> I've  got  problem  when  I add force to the body (dBodyAddForce).
> The
> > l>> force  is  added  (dBodyGetForce returs correct vector)but it
> takes no
> > l>> effects  in  the  simulation  step.  If  there  is no gravity the
> body
> > l>> doesn't move. Why? has someone any explanation? maybe someone had
> such
> > l>> a problem?
> > l>> Thanks for any ideas!
> >
> > ok I've found the reason of my problem - force vector was too small to
> > make effect, but I've got another question due to this: what are your
> > experiences of using forces? do you really have to put force vector
> > like: (10000,0,0) to see anything moving? What are the units of force
> > vectors?
> >
> > lazareer
> >
> > _______________________________________________
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