code: def turn_physical_on(self,ro=None,vo=None):
          
          self._roSet= True
          self._voSet= True
          if not ro is None:
              if _APY_LOADED and isinstance(ro,units.Quantity):
                  ro= ro.to(units.kpc).value
              self._ro= ro
          if not vo is None:
              if _APY_LOADED and isinstance(vo,units.Quantity):
                  vo= vo.to(units.km/units.s).value
              self._vo= vo
          self._orb.turn_physical_on(ro=ro,vo=vo)
docs: NAME:
  
             turn_physical_on
  
          PURPOSE:
  
             turn on automatic returning of outputs in physical units
  
          INPUT:
  
             ro= reference distance (kpc; can be Quantity)
  
             vo= reference velocity (km/s; can be Quantity)
  
          OUTPUT:
  
             (none)
  
          HISTORY:
  
             2016-01-19 - Written - Bovy (UofT)