Squid Jet Physics

[OctoPussyAZ]

PZ Myers at Pharyngula.org has a neat excerpt of a paper up on his blog, talking about squid jets (and his own inability to follow the math behind the analysis)...

http://pharyngula.org/index/weblog/comments/defeated_by_the_squid/

He does cite the papers at bottom -- I assume they are not directly available online.

 

[Fujisawas Sake]

Actually, this is pretty cool.

I think that its actually a biological application of Bernoulli's principle, with a few mods taking into account other forces. I could go into more detail if you like.

 

[Feelers]

So can they only use one jet? And then have to stop and refill before using the jet again?

I was thinking this just because the intake for the jet is also at the head end - so sucking in would create a pull forwards - equal to the push backwards?
I dont know anything really about hyrdodynamics - Fujisawas Sake if you could go into a bit more detail I'm interested

I had a look at http://home.earthlink.net/~mmc1919/venturi.html to see what Bernoulli's principle was, but I dont see how it can be used to jet away multiple times? My theory was that maybe the water is drawn in from above and below then squirted forwards?

 

[OctoPussyAZ]

More via Pharyngula

This is from Squid Blog (never heard of it before today) -- thanks again to PZ at Pharyngula...

http://www.squidblog.net/2005/11/22/jet-flow-in-steadily-swimming-adult-squid/

Feelers: It seems to me that, although the intake also faces backwards, it is of enormous area relative to the jet nozzle... But what do I know?

The writer on SquidBlog is talking about some arcane Vortex ring propulsion stuff, anf the conclusion is, after experiments, is that the squid does not use this method.

 

[OctoPussyAZ]

Sorry, here is primary link

http://jeb.biologists.org/cgi/content/full/208/6/iii

 

[Feelers]

OctoPussyAZ - I was just thinking of the idea of getting out what you put in - I'm trying to think about it in terms of floating through space.

If you catch a ball (intake water) you gain its momentum(in this case get sucked towards where you are intaking water), then if you throw the ball(faster than you caught it) away in the direction you caught it from- you will have a net gain in momentum.

At least thats how I can figure it - and like you say Bernoulli's Principle is used to increase the velocity of "throwing the ball".

 

[um...]

Feelers, I would agree that there's probably a shot of 'negative' momentum on the intake, although it's probably tiny compared to the momentum gained from the jet. I took fluid mechanics a million years ago, and I can't seem to remember whether there would be any advantage to a high velocity flow over a slower flow of greater volume. Power? Is it easier for muscle to move a small amount of water very quickly in a rapid succession of contractions? I have a pdf of the article, which I downloaded a week or two ago, but I forgot all about it until yesterday when PZ brought it up (I'm moving in two days--causes some distraction).

Must go pack. Too bad the textbooks have been sealed for a week.

 

[bigGdelta]

I was going to use an example much like feelers' (two kids playing catch) but got called away from the computer and he beat me to it.

 

[Feelers]

Its interesting that the squid doesnt have the intake at the posterior end.

 

[dub_doctor]

This is from Squid Blog (never heard of it before today) -- thanks again to PZ at Pharyngula...

http://www.squidblog.net/2005/11/22/jet-flow-in-steadily-swimming-adult-squid/

Feelers: It seems to me that, although the intake also faces backwards, it is of enormous area relative to the jet nozzle... But what do I know?

The writer on SquidBlog is talking about some arcane Vortex ring propulsion stuff, anf the conclusion is, after experiments, is that the squid does not use this method.

Actually, I was just quoting this article: http://jeb.biologists.org/cgi/content/full/208/6/iii

[Edit: Sorry OctoPussyAZ, I didn't see your next post]

Myself, I can't make much of the original article.

I'd still love someone to make an animation of squids in motion, to demonstrate the conclusions of this paper. The abstract-style pictures in the original article are so uninformative to the non-expert.