text: rotation will be quite a “curve ball artist” 
  the golfer that cannot control the lateral mo- 
  tion of the club face striking the golf ball will 
  impart an uncontrollable spin and have trouble 
  with a “hook”  or “slice.” 
  
  While a rotating cylinder can produce a net 
  from the circulatory flow, the method is 
  lift 
  relatively 
  inefficient and only serves to point 
  out the relationship between lift and circula-, 
  tion. An airfoil 
  with relatively high efficiency and the process 
  is illustrated 
  If a symmetrical 
  airfoil 
  is placed at zero angle of attack to the 
  airstream, the streamline pattern and pressure 
  distribution give evidence of zero lift. HOW- 
  ever, if the airfoil 
  is given a positive angle of 
  attack, changes occur in the streamline pattern 
  and pressure distribution similar to changes 
  caused by the addition of circulation 
  to the 
  cylinder. The positive angle of attack causes 
  increased velocity 
  an increase in upper surface suction while the 
  decreased velocity on the lower surface causes 
  a decrease in 
  lower surface suction. Also, 
  the 
  upwash is generated ahead of the airfoil, 
  forward stagnation point moves under the 
  leading edge, and a downwash is evident aft 
  The pressure distribution 0” 
  of the airfoil. 
  the airfoil now provides a net force perpendicu- 
  lar to the airstream-lift. 