[ODE] problem with adding forces

[Martin C. Martin]

-9.8 is the acceleration due to gravity.  The gravity force varies from
one object to another.  The formula that gives you the force of gravity
from the acceleration due to gravity is:

F = m a

- Martin

lazareer wrote:
> 
> 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
> 
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