text: FRICTION EFFXTS 
  
  &--v~se the +ir hAas .~~.v-~c~~v air -7ill --- 
  I. 11 -11 
  counter resistance to flow over a surface. The 
  viscous nature of airflow 
  reduces the local 
  velocities on a surface and accounts for the 
  The retardation of air 
  drag of skin friction. 
  particles due to viscosity is greatest immedi- 
  ately adjacent to the surface. At the very sur- 
  face of an object, the air particles are slowed to 
  a relative velocity of near zero. Above this 
  area other particles experience successively 
  smaller retardation until finally, at some dis- 
  tance above surface, the local velocity reaches 
  the full value of the airstream above the sur- 
  face. This layer of air over the surface which 
  shows local retardation of airflow 
  from vis- 
  The 
  cosity is termed the “boundary 
  characteristics of this boundary layer are illus- 
  trated in figure 1.24 with 
  the flow of air over 
  a smooth flat plate. 
  
  , .“I”., L, , 
  
  The beginning flow on a smooth surface gives 
  
  evidence of a very thin boundary layer with 
  the 
  in smooth laminations, 
  The boundary layer flow near the leading edge 
  is similar to layers or laminations of air slid- 
  ing smoothly over one another and the obvi- 
  ous term for this type of flow is the “laminar” 