Reptile & Amphibian Forums

This does not need to turn into a huge debate, but that last thread had me doubting some things and had me thinking a little more.

Would 50 pounds per square inch be the same as 100 pounds per two square inches and 200 pounds per four square inches? It would make sense that it would but the difference between PSI, force, and pressure mentioned before had me thinking this all sounds too much like pressure. Thanks

The recent giant snake special mentioned the anaconda was exherting 90 pounds per square inch on the live duck. The total snake (or surface they were measuring) was then exherting 9000 pounds "of pressure" on this duck. You would think the things head would pop right off or it would just explode. I have heard lots of bones cracking from constrictors prey before but 9000 lbs seems like quite a bit.

...to answer the first part, yeah, on average, they're all the same pressure...50 psi..50pounds of force exerted per square inch of area.

The anaconda's total force exerted is 9000lbs...thats not the pressure. Keep in mind, the force exerted is never uniform, and it results in differential pressures being exerted all over different points on the duck. Basically, the internal forces pressing outward on the duck will balance the pressure exerted by the snake.

90 psi seems reasonable, if you think of being squeezed by a python or boa wrapped on your arm---I've had one close call with a burmese during a feeding mishap--it really squeezed my arm and caused blood to squirt out through the teeth punctures--so they do squeeze pretty tight!

Anyone who has been SCUBA diving and experienced a mask squueze at deep depths, knows what that feels like--similar to a snake squeezing. I had a mask squeeze at 120ft once, which ruptured vessels in my eyes...it was somewhat painful, but since water pressure doubles every 33ft...at ~120 you are at 4.5x atmospheric( 120/33= 3.6 1 for the air pressure at sea level), so 4.5 x 14.7psi = 66psi....so I would say, YES, that 90 psi of pressure is in the ball park. Again, pressure isn't exerted...its the result of a FORCE being exerted.

LOL, I was going to suggest on the thread below, that perhaps our next topic for dicussion be "DENSITY".

>>Would 50 pounds per square inch be the same as 100 pounds per two square inches and 200 pounds per four square inches?

Exactly. Divide your forces in Pounds by the area in Sqaure Inches and you get 50 Pounds per Square Inch (psi) in all 3 cases.

>>It would make sense that it would but the difference between PSI, force, and pressure mentioned before had me thinking this all sounds too much like pressure.

Just to be clear, I was discussing exactly two quantities in the earlier thread: 1) Force 2) Pressure

PIS is not a third quantity, it is the English unit of pressure.

>>The recent giant snake special mentioned the anaconda was exherting 90 pounds per square inch on the live duck. The total snake (or surface they were measuring) was then exherting 9000 pounds "of pressure" on this duck.

They were using the common informal English usage of the word "pressure" which is used interchangeably with the word "force". In a more formal context, "pressure" and "force" are two disting quantities. Thus much of the confusion above.

>>You would think the things head would pop right off or it would just explode. I have heard lots of bones cracking from constrictors prey before but 9000 lbs seems like quite a bit.

They got that number by reversing what you did above, except that in this case they are adding up all the forces on all parts of the duck pushing in different directions (multiplying 90 p/si by an estimated 100 si to get 9000 p). The result is a number that sounds impressive but is of almost no real significance. The significant quantity here is the 90 psi.

That does sound like a lot of pressure, but I don't have a feel for how close that is to making the duck's head explode. I have seen eyes literally pop out o the sockets of mice and rats while being constricted...

P.S. Note that in that show Dr. Barr was actually using a pressure gauge attached to an air filled bladder and correctly stating the result in terms of "psi". In his "Bite Force" show, he uses a force gauge and correctly referrs to the result in terms of "pounds". In every other similar show I can think of a force gauge was used and the result incorrectly given in "psi" which makes no sense whatsoever, thus more confusion.

>>PIS is not a third quantity, it is the English unit of pressure.

I meant PSI, of course.

I have been giving snake lectures to schools (high school biology and a few elementary classes) for the last few days and the strength of constrictors was a part of the talks. I wanted to be sure I was using the correct units. The anaconda study did use a bladder (not a force guage like on the animal face off shows).

Even with 9000 lbs around every angle of the duck...it would equal at least a metric ton in each direction and I would think that would be enough to pop its head off. I have seen organs pop out their rectum and eyes pop out of their head...but I guess after seeing the numbers I am surprised I do not see more happen.

>>Even with 9000 lbs around every angle of the duck...it would equal at least a metric ton in each direction and I would think that would be enough to pop its head off.

One thing to keep in mind is that an animal is not a bag of liquid. The blood is in vessels, which colapse way below 90psi, possibly preventing the blood from flowing out of the compressed tissues. I'm really speculating here though...but it sounds good.

From one of your previous posts:
"My blood pressure runs somewhere around 1.8 psi (125 mm Hg). If 0.11 psi were enough to puncture human skin I would have exploded in a cloud of red mist long ago... "
This conversion of psi to mmHG has been bothering me. How is it done?

>>From one of your previous posts:
>>"My blood pressure runs somewhere around 1.8 psi (125 mm Hg). If 0.11 psi were enough to puncture human skin I would have exploded in a cloud of red mist long ago... "
>>This conversion of psi to mmHG has been bothering me. How is it done?

Well, if you don't zone out and mix up your mmHg and millibars like I did above, you multiply psi by about 51.7 to get mmHg or divide mmHg by 51.7 to get psi. 125 mmHg/51.7 = 2.4 psi (not 1.8).

Oops...

Was that the question, or was it more along the lines of "how is mmHg a measure of pressure"?

Thanks.
"Was that the question, or was it more along the lines of 'how is mmHg a measure of pressure'?" Yeah right. LOL.

The best way to appreciate pressure is to watch stupid people play with it! I fondly remember some idiot who thought that any air hose is as good as the other. It was funny watching him fighting with a ruptured hose that he had no control over....the massive blisters on his arm were even funnier. Luckily for him the compressor ran out of pressure. Oddly enough, the compressor didn't weigh nearly as much as the pressure it spewed.
Shane
-----
Shane's Herp Lifelist
http://www.geocities.com/shane77@sbcglobal.net/my_page.html