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Re: [Phys-l] swimming



Well, there are *limits*, of course (as you prove w/ your air gedankenexperiment). Fluorinated hydrocarbons (think the liquid stuff that people breathe in The Abyss) _can_ be oxygenated enough to allow fish to survive within them (it's been done, and with mammals) for quite a while.

I don't know what the swimming mechanics were observed to be, but one of the big problems is that the density is so high that the fish bob right to the surface without counterweights.

The following doesn't bear directly on your student's question, but it probably will, eventually, and it's a classic of gorgeous scaling arguments (yes, J.D., not everything is such) and good teaching: http://jilawww.colorado.edu/perkinsgroup/Purcell_life_at_low_reynolds_number.pdf>



/**************************************
As a species, we are forever sticking our fingers into the electric socket of the Universe to see what'll happen next. It's a trait that'll either save us or kill us, but by god it's what makes us human beings. I'd rather be in the company of people who look at Mars than people who contemplate humanity's navel -- other worlds are better than fluff. ~~Sir Terence David John Pratchett
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________________________________
From: Anthony Lapinski <Anthony_Lapinski@pds.org>
To: phys-l@carnot.physics.buffalo.edu; tap-l@lists.ncsu.edu
Sent: Tue, March 30, 2010 7:15:31 AM
Subject: [Phys-l] swimming

A curious/brilliant student asked me a random question during my
electricity topic. She wanted to know if it would be easier or harder to
swim in a pool with a more dense liquid (than water). After class, we
reasoned that it would be harder to move, but your hands could provide
more force on the liquid to propel you forward. You would also not sink as
much. With a less dense liquid, it would be easier to push the liquid
back, but the liquid's reaction force would also be less. There would also
be more friction since you would sink more into the water. We imagined
turning off gravity and trying to "swim" in a sea of air and not moving
too far.

After our discussion, we both figured that it would be easier to swim in a
more dense liquid, but we could not do an experiment to prove this.

Any thoughts/demos for this one?

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