Date: Wed, 13 Nov 2002 11:19:03 -0500

Author: "Jason St. John"

Subject: Re: Vortex Cannon


We cut a hole about one foot across in the bottom of a 55 gal. Rubbermaid
trash barrel (diam. of bottom: ~20 inches). Over the open top, we
stretched a sheet of latex, and it's held in place (somewhat) by the
putting the lid over it tightly. (All but the outer rim of the top was cut
out to permit access to the membrane.) Loaded from a fog machine, it sends
rings all the way to the back wall of the lecture hall (about 50ft), and
gradual compressions send slow smoke rings which can be 'shot down' by the
faster smoke rings, which have so much more integrity that they survive
the 'collisions'.

A mock-up with two very small holes (1/2" diameter) spaced far apart on a
5" diameter Al plate at the end of a 16" cylinder was supposed to be
piston-driven, but it can only produce jets of fog or else very very slow
smoke rings which lose integrity within a few seconds. Perhaps this is
because of the small hole diameter, and it probably isn't helped by the
holes being threaded holes in a plate almost as thick as their diameter.

I heard that Feynman was into these things.
Jason St. John 617.353.2634
Boston University Physics Lecture Demonstrations

On 2002-11-12.19:32 sent:


I built a vortex cannon this past weekend out of a 5 gal. joint compound
bucket & an old tire inner-tube. For the fog I'm using a heating element
from an old toaster oven & fog juice inside the bucket. It fogs up ok, but
my rings are kinda small.

Has anyone experimented with hole-size? What's the biggest hole I can make
and still get a good smoke-ring? I would imagine that there's some proportion
between bucket diameter and hole diameter?

Erik Herman

University of Arizona
College of Science
Teacher Prep Program