1b. The trash can’s lid will only take
this abuse for so long before it cracks
and falls apart. You can replace it with
a snappy new plastic diaphragm. Start
by gathering the center of a trash bag
or tarp around a ball and using a small
bungee cord to tie it off into a knob.
TIP: A light thump makes a slow-moving
vortex, while a hard thump makes a fast-moving but less stable vortex.
1c. Duct-tape the diaphragm all around
the top of the can with the knob in the
center, leaving some slack. Stretch the
large bungee cord across the handles.
To fire, pull back and release the knob.
NOTE: You can experiment by cutting the
hole larger. This makes larger vortexes
that move more slowly.