[ODE] Mass etc.

[Yefei He]

Hi, 

    Here are a few more newbie question from me. 

    1. Does mass have units? I assumed it is in kilograms and assigned 1000 
to an object and let it rest on top of a plane at the beginning. As soon as 
the simulation starts, the object falls under the plane as much as 4 meters 
below and then bounces back up. When I set the mass to 50, it works more 
realistic. What mass values should I assign to an object to match its real 
world mass, say a one ton car, on concrete road surface? Are there any world

parameters I need to set? 

    2. Does step size correspond to real world time? I'm running a visual 
simulation that renders at 60Hz, so presumably the step size should be
0.0167. 
But it seems that free falling objects fall rather slowly. I had to double
the 
step size to make it look more real. The gravity is set at (0, 0, -0.981). 

    3. Could somebody answer me if dBodySetLinearVel() and 
dBodySetAngularVel() sets velocities in the world frame coordinates or 
the body frame coordinates? They appears to be in world frame... If so, 
how do I apply roll, pitch and yaw rates? 

    Thanks, 

    Yefei