pz

Hey, now, that's no fair. Just because we lack the ability to comprehend the calculations of an expert in fluid dynamics like Vanderzyden is no reason to call us names.

I'm sure he'll resolve the contradictions between real world experience and his calculations. After all, they're numbers and formulae...they can't possibly be wrong.

Blinn

Okay, sorry for calling names; that was the first thing that entered my head after reading the line implying that amniotic fluid does not contribute to buoyancy. I'll try to read further the next time before calling John an idiot.

pz

Oh, you were calling John an idiot. I can't imagine why -- hasn't he just shown us his mastery of hydrodynamics? Man, those numbers and calculations sure are impressive.

Blinn

Absolutely. I understand it gets confusing around here sometimes, particularly with crossposting. The only thing he has apparently mastered is the ability to troll.

RufusAtticus

That's your major mistake. You need to calculate net transmural pressure, to see if it has any effect on the fetus. That is because gravity produces hydostatic pressure in both the amniotic fluid and the fetus' blood. Thus your above post only does part of the problem. Like I showed before, the net transmural pressure is delta_p = (r_out-r_in)*g*delta_h. So all you need to do to show that the effect of gravity is significant is to comapare the densities of the amniotic fluid and the fetus.

~~RvFvS~~

[ November 08, 2002: Message edited by: RufusAtticus ]</p>

Vanderzyden

All,

It is widely known that the density of of whole blood is very nearly equivalent to water:


Rufus,

I don't know how to respond. What is your point?


PZ,

I appreciate your civility. Yes, atmospheric pressure is approximately 14.7 [lb/ft3] = 760 [mmHg] under typical warm, sunny conditions. But you add it to hydrostatic pressure. And, you add it to the all of the parts of the mother, the fetus, the uterus, etc. It is uniformly applied because of the effects of gravity which is a main point I have been making here. I believe all of my explanations and simple calculations in the last post consider hydrostatic pressure only.

Yes, diving is a pertinent topic, where:

Absolute pressure = Atmosphere + Hydrostatic

<a href="http://www.scuba-doc.com/physics.htm" target="_blank">http://www.scuba-doc.com/physics.htm</a>


John

[ November 08, 2002: Message edited by: Vanderzyden ]</p>

Dr Rick

John is correct on this one point, and I was wrong.

My error does not change the fact that John is completely wrong in asserting imagined flaws in the improvements proposed for the fetal circulation.

His "fluid dynamics" argument would make it impossible for a fetus to survive its mother lying down overnight.

Rick

pz

Yes, I know. Sarcasm is lost on some people.

You haven't addressed the fundamental point of all of the responses to your calculations: the implications of your numbers are contrary to common sense and everyday experience. My lungs don't explode when I go swimming, babies can't stand on their head for 3 months without ill effect, pregnant women don't have to maintain a single constant posture lest the force of gravity kills their fetus. Yet you seem to be oblivious to these failings of your numbers.

You also haven't addressed the issue of fetal circulation in this set of calculations. They do nothing to support any of your contentions. Are we supposed to be convinced because you can solve a simple algebraic equation, even if you don't seem to know how to apply it appropriately?

Finally, I thought Coragyps' simple problem cut right to the heart of the issue, but you didn't even consider it. If you have a pipe in a lake, how much force does it take to pump water down the pipe relative to pumping it up?

scigirl

I just want to say thanks to everyone (yes even you John )for "learning me" about physics again - this is great.

I was thinking about this thread this morning (I read John's reply right before I went to bed) and I kept thinking some of the same things that have been pointed out:

1) John's calculations, to me, only seem to apply to that one position of the fetus (maybe his wife stood up the entire time she was pregant, but most women do lay down around 1/3 of the time! Plus the fetus moves.)

2) So what? Both "god" and "evolution," according to ID and evolution theory, are capable of desiging a complex circulatory system that can overcome the effects of gravity and whatnot.

Evolution, however, makes added predictions. A. These compensatations will look "jury-rigged" - like they were modified from another plan. B. We will see the more primitive plans present themselves in the embryo.

Aortic arches, among other things, in the fetal circulation seem to support A & B, and thus evolution, not intelligent design from scratch.

I'm still waiting for John's explanation as to how this argument
1) proves intelligent design or disproves evolution and
2) how his argument explains the survival of giraffes (which clearly do have a gravity problem but have the same placement of vessels as we do).

scigirl

MrDarwin

Excuse me???? The pressure exerted on the blood by an external fluid has nothing to do with how close the blood is to the skin. By this reasoning, a person who is submerged is unaffected by the pressure of the water around him.

Now carry on, and I will go back to lurking.