public Vector3f getGravity() {
        return getGravity(null);
    }
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