code: def turn_physical_on(Pot,ro=None,vo=None):
      
      if isinstance(Pot,list):
          for pot in Pot:
              turn_physical_on(pot,ro=ro,vo=vo)
      else:
          Pot.turn_physical_on(ro=ro,vo=vo)
      return None
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:
      
          2016-01-30 - Written - Bovy (UofT)