public Vector3f getGravity(Vector3f gravity) {
        if (gravity == null) {
            gravity = new Vector3f();
        }
        rBody.getGravity(tempVec);
        return Converter.convert(tempVec, gravity);
    }
Sets the mass of this PhysicsRigidBody, objects with mass=0 are static.

@param mass the desired mass (&gt;0) or 0 for a static body (default=1)
jme3-jbullet/src/main/java/com/jme3/bullet/objects/PhysicsRigidBody.java