How to make a vortex cannon (and why!)

October has been a busy month of thesis-writing and conference planning (for a postgraduate conference “Engaging with Engagement” or “EwE” for short) but November is when life will really get exciting.  Julia has two masterclasses to give to S2 (13 year old) pupils, and we decided it was time to show that we meant business.  No more scrounging around the chemistry labs for bits of dry ice to put in the puny Airzooka.  It was time for a heavy duty smoke machine and a GIANT VORTEX CANNON.

I should probably say why this is necessary for a masterclass about knots, or you might think I’m slightly insane.  Well, once upon a time there were three great physicists in Scotland: Kelvin, Maxwell and Tait.  They wanted to understand the different elements in the periodic table.  What made an oxygen atom different from a calcium atom? One day Kelvin saw Tait experimenting with a vortex cannon; using a pungent mixture of ammonia and sulphuric acid he made smoke rings that could travel many metres across the room.

The scientists at that time believed in the existence of the luminiferous æther.  They thought that light was a wave, and that waves had to travel through something (you can’t have water waves without the water!), so this invisible substance was called the æther.  When Kelvin saw the smoke rings, he immediately had a great idea: that different chemical elements were different knots and links of the æther!  Not only was the idea beautiful and simple, but there was some evidence for it too.  Sodium, for example, has two distinct lines on its emission spectrum, indicating that it was made up of two linked knots.  Genius!

Maxwell went on to develop the physics of this theory while Tait started tabulating all the possible knots he could think of.  Thus was knot theory born!  Sadly the physical theory was proven to be wrong, because it was shown at the end of the 19th century that the æther could not exist, but the mathematics lived on and grew to great new heights.

For anyone who wants to read a detailed account of this story, there is a very good article by Dan Silver, in which he actually recreated the original vortex ring experiment!

Now, I like to tell this story to the kiddiewinkles, and I want to make it big and dramatic.  So I Googled “how to make a giant vortex cannon”, and this is what happened next.

1) I bought large garden bin. Bin

2) I assembled some scary looking tools. Tools

3) I needed to cut out a hole, about 6 inches in diameter, in the bottom of the bin.  This was not going to be easy!  A very sharp Stanley knife might have been my best bet, but I didn’t have one of those.  The way I did it was first to cut out a little hole using my biggest baddest meat cleaver:

Make Hole

Then I removed the saw from the hacksaw, put it into the hole and started sawing my circle:Cut a hole

This was almost certainly not the best way of doing things, but I got there eventually!The completed holeI then filed down the rough edges and used a little scalpel thing to make the hole a bit more circular.  Don’t want the kiddies cutting themselves on sharp plastic!

[At this point, I thought I could get some artistic photos since the dustbin was open at both ends.  In the end I went for a James Bond style shot:Bond photoThe name is Bond.  Haggis Bond.  Double – 0 – sheep.]

4) I bought a cheap shower curtain:Shower curtain

5)  I covered the other end of the bin (i.e. the top end) with the shower curtain and secured with gaffer tape, cutting off the excess curtain.Membrane attached

6) I bought a smoke machine (Maplin, about £35) and got psyched up for hours of smoke-ring-generating fun!  (You put the smoke in, then bang the shower curtain end to push the smoke out through the hole, creating vortex rings.)

Unfortunately (and I’m really really sorry!) I got so excited about testing the cannon at this point that I forgot to remind Julia to keep taking photos/video.  So I haven’t got photos of the cannon in action, but when it finally gets used in a masterclass I will be sure to get some footage!

[Many thanks go to Peter Reid of SCI-FUN for supplying me with the hacksaws, scalpel, file and gaffer tape, and to Kizzy The Dog for accompanying me on the expedition to get the smoke machine.]


2 responses to this post.

  1. Posted by lns on November 1, 2010 at 12:02 pm

    This makes me think so much of the excellent 2-D Goggles episodes with Ada Lovelace and Charles Babbage and their adventures in the criminal underworld of the 19th century…

    I can somehow just see Ada wielding a Vortex Cannon… alternatively I am trying hard to envision Haggis with riding-breeches on all four legs but it’s not working terribly well…


  2. Posted by Hugh on November 1, 2010 at 1:59 pm

    Isn’t there a similar theory in current physics, that fundamental could be knots in spacetime? Would be interesting to see the old theory getting reused!


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