My bad, same difference. Your body's volume decreases by the same amount the volume of "water" increases. Zero-sum.
lurker wrote:And in the scenario you describe no organs shift downwards, the skin doesn't shift in at all, and the space vacated by the urine is now devoted to?
Nothing. The bladder contracts, all right some organs may shift, but I doubt you could accurately calculate that, and it's probably random enough to be different every time you try to measure. The human body doesn't have random open holes, if something goes away it is neatly closed up - watch an autopsy vid (I've got a top-of-the-line one off of PirateBay), the human body fits together like a giant bunch of wobbly, fleshy Lego bits.
If you drag twenty balloons under the water, they have a mass of practically nothing, but have as much volume as the same volume of heavy cannonballs.
The only difference is in the force required to keep them under the water, which isn't relevant to Boirunner's silly question.
In the pissing example, the water level does not change, because you're merely moving fluid from one place to another, with no net change in volume at all.
Oh, sure, in the longer term, water will then move out of the GI tract through the kidneys and refill that bladder, which will raise the water level in direct proportion to the amount of liquid involved vs. the volume of the bathtub (i.e., if it's wider, it will rise less).
It's no different than swishing the water around with your hand- you're exerting force on the liquid, but you aren't changing the volume, other than a teensy amount of very temporary compression that quickly reverts to Brownian motion.
So, does a polar bear pooping into the water raise the water level? http://www.indavideo.hu/video/Jegesmedvefos (video of said act)
Ban all polar bears! They are causing the oceans to rise!
Oh, sure, in the longer term, water will then move out of the GI tract through the kidneys and refill that bladder, which will raise the water level in direct proportion to the amount of liquid involved vs. the volume of the bathtub (i.e., if it's wider, it will rise less).
Only if you ate or drank.
Also how deep is the bath? If we don't know the parameters we can't calculate. But basically your body is full of fluid, so nothing there is going to compress; therefor filling your bladder expands your abdomen- (don't believe me? put on some tight jeans and a very tight belt and drink 3 cans or red bull and a half a litre of water. Then, just when you think you are gonna piss yourself- loosen the belt and unzip the jeans.) therefore the total volume of additional fluid (body plus piss) doesn't change.
The abdominal muscles would probably play a part in keeping the post-pee body's shape therefore making the bladder a mix between a bottle and a plastic bag. So I think the water level would rise but not as much as the volume of pee.
Boirunner wrote:hint: after i pee, what is where my pee used to be?
In the Swimming Pool, which gets back to you, if you take a gulp of (what you think is) water. So everything is going full circle- now open that can of 4 Times circled DinousaurierPiss called Beer and accept the fact.
