[ODE] Simple questions

[David Whittaker]

> I've just started using ODE today and I have a few basic questions.
>
> 1 - What's a torque and what is it used for?

Torque is the amount of "twist" a body exerts on another... if that makes
sense.  For example, when you open a jar, you exert a torque on the lid
(as opposed exerting a force on a can when you smash it).  The engine of a
car exerts a torque on the drivetrain, axle, and eventually wheels to get
them to spin.

> 2 - If I call dBodySetLinearVel( ... ), my object moves in the specified
>  direction (while falling since it's in the air).  However, if I call
> dBodySetAngularVel( ... ) instead, it doesn't do anything (my object
> simply  falls in a strait line).  What is the second function supposed
> to do and in  which situation should it be used?

Angular velocity is a similar concept.  It's the speed at which that
object is spinning.  It probably looked like it wasn't doing anything
because it was a sphere, and it's hard to see round things spin... at
least that's my guess.  It is represented by three numbers, the x, y, and
z coordinate of the axis that it's spinning around.  The magnitude of that
vector (i.e. the distance from 0 to point <x,y,z> or sqrt(x^2 + y^2 +
z^2)) determines how fast it is spinning around that axis.

> Thanks!

Any time,
David

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>
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