leaving 20 - 30 cm of unwound string between the tube and the meterstick, as shown above at right.  Starting with plenty of slack, rapidly jerk the stick to the side at an angle of 20 degrees above the horizontal.  The tube will spin as the string unravels.  The Magnus effect will make the tube take off and fly in a "loop-the-loop" with a surprising amount of lift due to the Magnus, or Bernoulli effect..  The string must be wound so that the tube will have a backspin when the string is snapped.  Practice this in the EMPTY classroom first.  Be sure to clear out students from where the tube will come down, because it comes down hard.  A 2 m long, 4 cm wide strip of cloth in place of the string works well for higher loops and a faster tube.