text: Figure 2.32 illustrates the typical variation of 
  the aircraft 
  fbrces acting on 
  the various 
  throughout the takeoff roll: 
  If ‘it is assumed 
  that 
  is at essentially constant 
  angle of attack during takeoff roll, CL and Co 
  are constant and the forces of lift and drag 
  vary as the square of the speed. For the case 
  of uniformly 
  accelerated motion, distance 
  along the takeoff roll is proportional also to 
  the square bf 
  the velocity hence velocity 
  squared and distance can be used almost synon- 
  omously. Thus, lift and drag will vary lint 
  from 
  arly with dyriamic pressure (4) or P 
  the point of beginning takeoff roll. As the 
  friction coefficient -is esscnti&y un- 
  rolling 
  ftiction will 
  the rolling 
  affected by velocity, 
  vary as the normal force on the wheels. At 
  zero velocity, the normal force on the wheels 
  is equal to the airplane weight but, at takeoff 
  is equal to the weight and 
  velocity, the lift 
  the normal force is zero. Hence, rolling 
  fric- 
  tion decreases linearly with 4 or Vz from the 
  beginning of takeoff roll and reaches zero at 
  the point of takeoff. 