Okay, so here’s what I meant about Bernoulli’s Principle being attached to squid physics:
Bernoulli’s principle deals with fluid dynamics, pressure, and overall conservation of energy. It also deals with Newton’s Third Law of motion – that for every force there is an equal and opposite force. While Bernoulli’s work deals mostly with constant flow rate, we can modify this a little bit.
Think of a squid mantle roughly as a curved tube with a large opening and small exit. Water goes in one end and comes out the other at a greater velocity, since the amount of water going in has to equal the amount coming out (This isn’t exactly the case, but close enough for government work, as goes the old saying).
All types of fluid dynamics deal with a conservation of energy. Basically, energy going in has to be equal to energy going out. Amount of water entering in through large entrance is the same amount as water exiting through smaller tube end. It’s the same principle as using your thumb to jet water out of a garden hose. The water being forced through the small siphon exerts a force in the direction opposite the incurrent flow of water, causing the squid to jet “forward” (Newton’s Third Law).
Also, if you take into account muscular mantle contraction and relaxation, those add more energy to the system, therefore you get a greater speed for jetting.
I wonder if squid have mastered something akin to “circular breathing”? In humans, its something woodwind and brass players use to keep breathing while exhaling. In squid, it would mean that some water could enter the mantle while being expelled through the siphon.
Bernoulli’s principles could also be used for determining the relationship between fin morphology and swimming energetics. For example, the four main forces in fluid dynamics are thrust, drag, lift, and weight. In an airplane, thrust comes from engines and tailwinds, drag comes from your coefficient of friction, lift comes from greater air pressure under the wing than above (another one of Bernoulli’s concepts), and weight is self-explanatory (The above example treats the atmosphere like a fluid – and that is exaclt what the atmosphere is). Well, do squid use their fins for powered swimming? Does the speed of the squid depend on the size of the fins? Is there an optimum morphological speed limit to each squid depending on what layer of ocean it inhabits?
Food for thought.
John