Re: Floating and sinking

[Leigh Palmer <palmer@sfu.ca>]

I got an answer for Ludwik on this one:

> Leigh:
>
> Some fish can expel air through their anus when they dive, causing them to
> fart (eg herring). Other species have to resorb the air through their
> circulatory system, obviously a much slower process so they have to fight
> against their own buoyancy when diving. This stuff is in any ichthyology
> text; I can loan you some.
>
> Larry
>
> Lawrence M. Dill, FRSC,
> Professor and Director,
> Behavioural Ecology Research Group,
> Dept. of Biological Sciences,
> Simon Fraser University
> Burnaby, B.C. V5A 1S6
> CANADA

I have some followup questions which I will send to him, too. The Cartesian
diver example tells me that as a fish descends it becomes less bouyant.
This could lead to a runaway feedback in which the fish couldn't reinflate
its swim baldder fast enough to stay bouyant, and an explosive problem as a
fish ascends and becomes increasingly bouyant, perhaps faster than it can
reabsorb the gas from the swim bladder. I have a picture of a herring rising
like a rocket through the water.

Really, this is an interesting problem. Why don't you high school teachers
dispose of that Bernoulli nonsense (as applied to airfoil lift) and
substitute something like this! Observations can be made; experiments can
be done (even with live fish if the ethics people don't get to you). The
vivid imagery I propose above will attract interest, I'm sure! The physics
that would be learned is infinitely better than that silly factoid.

Leigh