// gives us vector to direction of target
            Vector3 inverseVect = Input.mousePosition;
            // calculate angle by which you have to rotate
            // Note -: This angle is calculated every Frame of FixedUpdate
            float rotationAngle = Mathf.Atan2(inverseVect.x, inverseVect.z) * Mathf.Rad2Deg;
// Now calculate  rotationVelocity to be applied every frame
            Vector3 rotationVelocity = (Vector3.up * rotationAngle) * rotationSpeed * Time.deltaTime;
            // Calaculate his delta velocity i.e required - current
            Vector3 deltavel = (rotationVelocity - rb.angularVelocity);
            // Apply the force to rotate
            rb.AddTorque(deltavel, ForceMode.Impulse);

//поворот физикой за мышкой в пустом пространстве
//(если смотреть на мышь)get right position of mouse if the camera is Perspective
    //подробнее goo.gl/Fc6icj
                Ray mouseRay = Camera.main.ScreenPointToRay(Input.mousePosition);
                float midPoint = (transform.position - Camera.main.transform.position).magnitude * 0.5f;
                Vector3 targetPosition = (mouseRay.origin + mouseRay.direction * midPoint);
    //get position of target object(если смотреть на объект)
                //Vector3 targetPosition = targetObject.transform.position;
    //gives us vector to direction of target
                Vector3 inverseVect = transform.InverseTransformPoint(targetPosition);
    //calculate angle by which you have to rotate.Note: this angle is calculated every Frame of FixedUpdate
                float rotationAngle = Mathf.Atan2(inverseVect.x, inverseVect.z) * Mathf.Rad2Deg;
    //Now calculate  rotationVelocity to be applied every frame
                Vector3 rotationVelocity = (Vector3.up * rotationAngle) * rotationSpeed * Time.deltaTime;
    //Calaculate his delta velocity   i.e required - current
                Vector3 deltavel = (rotationVelocity - rb.angularVelocity);
    //Apply the force to rotate
                rb.AddTorque(deltavel, ForceMode.Impulse);
    //служ. инфо
                Debug.DrawLine(transform.position, targetPosition, Color.magenta);
                print("targetPosition: " + targetPosition +
                    " targetObject.transform.position: "+ targetObject.transform.position +
                    " transform.position: "+ transform.position);