Magnus effect
A rotating cylinder in moving fluid is pushed to one side.
This is known as the Magnus effect. The forces involved are
the same ones that cause a baseball pitcher's curve ball
to be pushed to one side.
To demonstrate the effect begin by linking together end to
end about three rubber bands. Push one end of band A through
band B. Then push one end of A through the loop of the other
end of A. Grab the end of A that was pushed through and pull
it tight. Connected the third band in the same manner.
Place one end of the chain of bands against the outside of the
center of an empty bathroom tissue cardboard tube. Wind the
rubber bands around stretching as you wind. Wind over the end
that you began with so that it will be held in place. Go
around about three times. Hold the tube at its middle with one
hand. Stretch the rubber band out away from you with the
other hand. The tube should be horizontal. The stretched out
band should be about horizontal and perpendicular to the
tube. The rubber band should emerge from under the tube not
from over the tube. Release the tube. It will be flung away
spinning rapidly. The spinning will cause its path to curve
upward maybe doing a loop the loop or hitting the ceiling.
If the tube is too thin and crinkles, then reinforce it with
a heavy paper disc glued across the center of the tube.
An alternate design is to use wide masking tape to fasten
two plastic foam drink cups together bottom to bottom.
Wind the tape around two or three times. Use the cups in the
same way as the tube. At the end of the cups' flight they
seem to glide rather than fall to the floor.