Re[2]:[ODE] problem with adding forces

[lazareer]

Thursday, August 7, 2003, 1:09:54 AM, Adam wrote:

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

Thanks a lot for every answer,
everything's clear but something is still weird for me:
when I apply a gravity to the world (vector [0,0,-9.81]) body moves in
right way, but when I apply force to the body(not gravity in the world) (vector
[0,0,-9.81]) it doesn't move. why? are gravity and "nomrnal"
forces different in ODE ? to move body using "normal" force I have to
apply much bigger force vector than gravity.
Any ideas?

lazareer