Should I specify the "mass" or the "density" in the Physics nodes?

[omichel]

It seems the two possibilities are available, which one is the best?

[omichel]

It is more accurate to specify the mass if it is known. If you are modeling a real robot it is sometimes possible to find the mass values in the robot's specifications. If you specify the densities, Webots will use the volume of each bounding object (boundingObject field) volume multiplied by the density of the corresponding Physics node to compute each mass. This may be less accurate because bounding objects are often rough approximations.