

Vortex Cannon - ctingom
http://www.youtube.com/watch?v=IyAyd4WnvhU&feature=player_embedded

======
frossie
... and then the third little big actually put some mortar between his
bricks...

~~~
RiderOfGiraffes
So, he's firing vortex rings at 200mph from an acetylene powered cannon, and
you complain that he didn't use mortar on the construction to demonstrate the
impact?

Interesting ...

~~~
shpxnvz
_he's firing vortex rings at 200mph from an acetylene powered cannon_

Which, while sounding impressive, apparently is only powerful enough to knock
down things that are equally vulnerable to being bumped into by a toddler.

Perhaps it's just that the reaction of the host in that video seems a bit out
of proportion to the actual accomplishment?

~~~
RiderOfGiraffes
Thank you - I've learned something. I honestly hadn't believed that someone in
HN could fail to appreciate what's really going on here, but you've convinced
me that some people just don't find it impressive. Having built air-bazookas
of various sizes as an exercise in hands-on science at kids' roadshows and
exhibits, they (the kids) are _always_ impressed by the targeting, impact,
effect, and sheer unexpectedness of the vortex effect. Maybe I've become
overly infused with enthusiasm for these sorts of things by the naive
excitement that children get from this sort of thing. Maybe it's just so much
better doing yourself for real, rather than just watching it on a video. I
know a lot of experiments and demonstrations that are truly impressive and
awe-inspiring in real-life, but cause very little reaction when viewed on
video. The video experience immediately removes you from the personal
experience.

To better help me understand your mindset I looked at your profile. There
wasn't any information about you, just the two links. I was interested to see
that the first was about a web monitoring service, and even more interested to
see the result of visiting the second:

    
    
      There has been an error processing your request.
      SQLSTATE[28000] [1045] Access denied for user 'root'@'localhost'
        (using password: YES)
      Trace:
    
       ... <snip> ...
    

I would've sent that to you personally rather than posting it here, but, as I
say, your profile has no contact details. Just thought you'd like to know.

~~~
shpxnvz
The air canon itself is very interesting, and I don't fail to appreciate it.
I'd very much enjoy seeing a video or reading in-depth about how one is
designed and constructed, or about real-world uses for such a technology.

I do fail to appreciate a video that is entirely focussed on using one to
knock things down, when said things are obviously constructed to be as weak
and fragile as possible. Thus, the reaction of the presenter seems to me
somewhat contrived and incongruous. It appears on the face to be typical over-
the-top T.V. production and I, personally, don't find it particularly
impressive.

Since you are obviously involved in this stuff, do you have any links to some
material that talks about the technology itself? That I would appreciate.

~~~
RiderOfGiraffes
Let me start by apologising. My comments were snarky and I shouldn't've said
what I did. It's now too late to edit them, but perhaps it's better to let
them stand anyway.

With regards links, no, I don't have any links to pages explaining the
technology. The best I have is this one:

<http://www.eskimo.com/~billb/amateur/vortgen.html>

There's a lot of stuff scattered around, but I've never found a single,
coherent treatment.

The reason smoke/air/fluid rings happen, in short, is this. Throw a lump of
air forward. The air in front of it gets pushed outwards to let the lump
through. As the displaced air streams around the outside, it drags on the
lump, causing the front face of the lump to follow the displaced air. That
makes the front flow around the outside, and then the back comes forward
through the middle to replace the air at the front, and hence you get a
toroidal circulation.

(in truth it's more complex, but that's the basic idea)

Here's an animation that shows the idea.

<http://www.amasci.com/wing/smring.html>

That site has much that's poorly expressed, so don't take it all too
seriously.

Making air/fluid rings is pretty easy, just throw a lump at a sensible speed.
They turn up everywhere, but there are some surprises. Send a smaller, faster
ring after a larger, slower one. The faster one catches up and goes through
the larger one. The larger one even gets bigger to let it through, then
shinks, catches up and goes through the other. You can get "leap-frogging"
smoke rings, which is cool.

<http://serve.me.nus.edu.sg/limtt/video/leapfrog.mpeg>

All the basic fluid-dynamic ideas are Newtonian in principle and you can treat
air as incompressible, near frictionless marbles flowing around.

Until you can't.

ADDED IN EDIT:

Collisions between smoke rings are interesting, both head-on and oblique. Most
of the time you get a spray of smaller rings, each made half from one, half
from the other. Or so I'm told - I'm still hoping to get the opportunity to
explore that situation sometime.

HA! Found video:

<http://serve.me.nus.edu.sg/limtt/video/collision.mpeg>

[http://serve.me.nus.edu.sg/limtt/video/Oblique_collison_fron...](http://serve.me.nus.edu.sg/limtt/video/Oblique_collison_front.mpg)

[http://serve.me.nus.edu.sg/limtt/video/Oblique_collison_top....](http://serve.me.nus.edu.sg/limtt/video/Oblique_collison_top.mpg)

<http://serve.me.nus.edu.sg/limtt/#Video_Gallery>

Finally, bit puzzled as to why this comment is getting down-modded at the
moment since I'm trying to contribute interesting stuff. My guess it's the
same person who down-modded the grandparent to this comment, and wants to
punish it further. <shrug> I'll live with that - it was more snarky than I
intended, and inappropriate for HN. We all make mistakes.

~~~
frossie
Since I made the original objectionable comment I would just like to say that
shpxnvz explained my annoyance very well. The issue is not the technology, it
is the way they chose to demonstrate it by riffing off the three little pigs
but then cheating the demo to fit their narrative.

I personally detest this kind of "whizz bang gloss over the details" style of
science show. I am one of those sad and pathetic individuals who think science
and technology are intrinisically exciting without needing to resort to cheap
tricks. I also hate being told how to feel - the dude is the science show
equivalent of a laugh track and really grated on me.

There is an argument that one has to resort to this kind of presentation in
order to engage kids. I find this patronizing and it does not match my own
limited experience talking at schools, but I concede I could be wrong.

~~~
timthorn
If I remember the (full) episode correctly, the presenter went into a good
level of detail about the working of the cannon, showing a prototype in the
lab and explaining what was happening. What is on YouTube is just the
conclusion of the experiment. This is clearly a marketing clip; Bang Goes the
Theory is a pretty good attempt at a science show, and indeed is an Open
University show.

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donaq
It's some way off from being a weapon, I think. The bricks didn't so much blow
off as they fell off (from being blown off balance). Ok, I did not say that
very clearly. Still, awesome experiment.

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Malic
I want one. Much like a Bugatti Veyron, I have no idea when I would have the
opportunity to really use it or where I would safely store it but I want one
nevertheless.

~~~
ComSubVie
I think it is to big to mount it on a Bugatti Veyron, but it would be nice
(would the resulting Vortex Ring be faster by the speed of the car, or would
the car drive into the ring, if it is fast enough?).

