Friction (A+12)

  A+12+0 Blocks, with various surfaces slide on an inclined plane.
  A+12+1 Film: "A million to one", flea and dry ice puck, sound, 5 min.
  A+12+5 Weighted wood block dragged horizontally by force sensor.
  A+12+10 Plank oscillates on oppositely rotating bicycle wheels.