% sfg.m4
.PS
sfg_init( 1.2 )   # scale default size by 1.2
\small

Ft: sfgnode(,f(t),sfgbelow)
    sfgline(,1/K)
Y1: sfgnode(,y_1,sfgbelow rjust)
    sfgline(,K/M)
DDY2: sfgnode(,\ddot{y}_2,sfgbelow rjust)
    sfgline(,s^{-1})
DY2: sfgnode(,`\dot{y}_2=x_2',sfgbelow ljust)
    sfgline(,s^{-1})
Y2: sfgnode(,y_2=x_1,sfgbelow ljust)

sf = 1
  sfgarc(left_ from DY2 to DDY2,-B/M,below,,sf)
  sfgarc(left_ from Y2 to DDY2,-K/M,above,ccw,sf)
  sfgarc(left_ from Y2 to Y1,1,sfgbelow,,sf)

.PE