WARNING: Stupid question follows.
If I were to lay on the ground and someone put a 6 foot column of water over me that was perfectly Nars Glinley shaped, I assume that with gravity and all, it would hurt like hell. Why can I go swimming and not feel the same effect? Gravity is still pulling me and the water above me toward the center of the Earth. If I were to lie on the bottom of the pool, it still wouldn’t hurt.
What’s the difference? Obviously I’m missing something obvious.
The water that you’re under is under water as well. The same buoyancy that makes you float makes the water float as well.
OK. I’m going to have to try to wrap my tiny little brain around that one.
The same reason why you don’t feel the atmosphere crushing you.
If you just put the water on top of you, it would tend to squish you flat. That would hurt because tissues would bend and stretch out of their usual positions. When you are underwater you experience the same pressure on your body from all directions at once. For swimming pool depths of water, this doesn’t result in any significant distortion of your tissues and hence no pain.
Atmospheric pressure is about 16 pounds per square inch (psi). You don’t feel it because the inside of your body is at the same pressure - there is no net force pushing on you, and so you feel nothing.
As you dive in a pool, for the most part, your body (which is made mostly of solids and liquids) withstands the increasing pressures just fine (the solids and liquids react to the increased pressure without a significant change in volume, and so you feel no effect). However, gas does not resist compression without a significant change in volume, and so cavities in your body filled with gas will begin to collapse the deeper you go. At six feet in a pool, you can definitely feel the weight of the water on your ears and chest. At twelve feet, it begins to get uncomfortable, in my experience. It is possible to collapse a lung on a very deep dive, with improper technique, as well as do severe damage to your ears, sinuses, etc.
(note that trained divers use techniques to equalize the pressure in their ears and lungs with the ambient water pressure, relieving this discomfort - I’m referring to what happens if someone just jumps in a deep pool and swims to the bottom).
Right. If you have a column of water on top of you, all your bits and innards are going to go squish out the sides, because there’s nothing holding them in. When you’re under water, you’re being pressed inward the same amount on all sides, so there’s nowhere for your squishy bits to move. That’s essentially the difference between pressure and weight.
Not to mention that you are mostly water. And liquids as you know, can’t be compressed.
What can be compressed, however, are the various voids of air in your body. Mostly the lungs, inner ear, sinuses and so forth.
If you start swimming down around 10 -15 feet or so, you will start to notice the pressure.
I disagree with the above answers. Well, I’d go so far to say they are flat out wrong and come from people that don’t understand physics. Water doesn’t hurt because it doesn’t exert much pressure. 10 feet of water exerts a pressure of about 4 psi. To compare, my foot is about 12" x 4", which is 48 inches squared. Divide that into 200 pounds and you get about 4 psi. That’s why it doesn’t hurt. The weight is all there, but it is perfectly distributed over your body because water is a liquid.
To continue in this vein. Brief googling tells me that a human skull crushes at about 25,000 psi. If I am doing calculations right, that is about 6,000 feet of water. So somewhere between you swimming in a pool and having your skull crushed, I’d imagine it would start hurting.
:eek:
You are saying that if you stood on my testicles it wouldn’t hurt, because it is “only” 4 psi of pressure.
I calls bullshit. 4 PSI on the eyes, skull, solar plexus etc is more than enough to cause pain, yet as you point out, that is precisely the amount of pressure being exerted by 10 feet of water, yet it is utterly painless, indeed it is almost impossible to even feel.
So how do you explain that?
The extra pressure of even six feet causes more nitrogen to be dissolved in body liquids (present in our tissues). When you rise in the water too rapidly, the nitrogen comes out of solution and causes the “bends” which is quite painful, and possibly fatal. Yahoo Search - Web Search
Are your testicles 48 square inches? Because if they are anything like mine, they are 1x1/2 or 1/2 inches square at best, and round. Since they are round, they only contact part of the ground at one time. So if I step on your testicle, it’s 200 pounds divided by probably 1/10th of a square inch at best, or 2000 psi.
You’re wrong. 4 psi on the eyes, skull, solar plexus, etc does not cause pain as evidenced by people swimming with out pain.
Which is precisely what everybody else said, and precisely what you said was wrong.
Which is of course perfectly circular. Everybody else is wrong and you are right because clearly everybody else is wrong and you are right.
No, we have people like you who say 4 psi will hurt. Which is absolutely flat out 100% wrong.
No it’s not:
You: 4 psi hurts
Me: No, it doesn’t as evidenced by people swimming while experiencing 4 psi of pressure
treis, you’re wrong.
Even a few PSI can cause pain to compressible areas of the body, like eardrums and sinuses. When you take SCUBA lessons, you lear about all the different types of “squeezes” that can occur to gas-filled areas of the body. The reason that these areas hurt and others don’t at the same pressure has to do with the compressibility of gasses.
You disagree with the above answers, then say exactly what they said?
Let me try my approach to explain what some others have already said:
Tissues like our (solids and water-based liquids) adjust to pressure by increasing their own internal pressure. At sea level, we have 16 psi of air pushing down on our skin, and we have 16 psi of muscle/bone pushing up on our skin. In a shallow dive into your swimming pool, you might get up a total of 20 psi of water pushing down onto the skin, and now you have 20 psi of muscle/bond pushing up on the skin.
As long as the two are balanced, there’s no pain. Even if you are talking hundreds of psi - or thousands. Sperm whales can go from 16 psi to 1,400 psi with no damage. (This doesn’t work for humans because gas pockets change size under pressure and in people, this results in damage. Whales just let the gas pockets collapse. Maybe someday we’ll do some genetic engineering that will permit free-diving to the ocean floor).
Using the OP’s example of 4 psi of water placed on a person lying on the ground, you don’t have even pressure. There is 16+4 psi pushing down (the water, and the air pushing on it), but only 16 psi pushing horizontally (the air to your sides). Your body can’t find a happy medium there; if the internal pressure is at 16 psi, then the water crushes you from above. The internal pressure is at 20 psi, then your muscle/bone erupts horizontally. (i.e. you are squished).
To create another picture for the OP: imagine that you place a 4 psi amount of water in a hemispherical pile on top of you. Now the horizontal psi is the same as the vertical psi and there’s no problem.
What’s really wrong with this thread is all this talk of testicle standing.
The reason these things hurt is that they are a lot more sensitive than the rest of your body. So yeah, a couple psi directly on your spinal cord is going to hurt like hell, but that’s why it is protected. The only way your ear drums and sinuses are going to hurt is if their natural defenses fail. Besides, none of this answers the question of why swimming doesn’t hurt.
They said you don’t hurt because of the water’s natural buoyancy and the fact that your body doesn’t deform. That’s different from it doesn’t hurt because the water isn’t pressing hard.
The reason people can’t dive very deep has nothing to do with gas pockets expanding. It has to do with effects of breathing oxygen at such high pressures. Basically, at depth the air pressure is much higher, and this changes how much of the gases are dissolved in the blood. You get a high level of oxygen and all other gases in the blood, and this has detrimental effects. The bends are a different phenomenon and are only a problem on the way back up.
And, as noted previously, if you go down too deep your skull will crush like a tin can.
A ten foot high (by 1x1 ft) column of water weighs 640 lbs.
The ground pressure of an M1 Army tank is about 15psi, which is only equivalent to a depth of about 34 feet.
Mike Tyson can punch about 800-900 psi.
Given these options, would you rather get run over by a tank, have 600 lbs of scrap metal balanced on your head or punched by Mike Tyson?