Why do you get dry suit squeeze and not wet suit squeeze?

[Soggy]

Actually, if it were a frictionless, infinitely stretchable (I don't use the term "elastic" here, as that has a distinct and well-defined meaning in physics) drysuit, it wouldn't matter that the volume of air between your skin and the suit had changed. The suit would be squeeze-proof, as only the thickness of the insulating air would be affected. (This is assuming your undergarments are equally well made, of course, but the physics of fleece under compression are not within the scope of this post.)

The reason the decreasing volume of air *does* matter is that the suit is certainly not frictionless and infinitely stretchable. As a result, you get ridges and pinch points and all those material-related squeeze effects.

I think what you are meaning to say is, "Yes, you're right."

 

[markr]

I didn't say the pressure inside the balloon would be different. I said the volume inside the balloon would be different. You are inside the balloon. The balloon shrinks to fit the volume of gas inside. You can't shrink. You get squished.

The balloon shrinks to fit the sum of the volume of the gas and the volume of the person, the same as it does in the balloon filled with water. The only difference is in the balloon filled with water there isn't much change in the total volume because the water can't compress only the air spaces in your body can. The primary air space in your body is being maintained at the surrounding pressure by the regulator but any trapped gas not directly connected to your lungs would compress.

An additional point to consider (because this thread hasn't gone on quite long enough):
Why do you feel squeeze in a drysuit without sufficient air in it, but don't feel the squeeze when air is added? Adding air to the suit isn't going to decrease the pressure being applied to your body, so why does the squeeze stop?

 

[ClayJar]

I think what you are meaning to say is, "Yes, you're right."

Indeed.

(Hehe, I have a tendency to cover the theoretical when discussing the practical... it's the curse of the science nut. )

The balloon shrinks to fit the sum of the volume of the gas and the volume of the person...

That is well stated.

An additional point to consider (because this thread hasn't gone on quite long enough):
Why do you feel squeeze in a drysuit without sufficient air in it, but don't feel the squeeze when air is added? Adding air to the suit isn't going to decrease the pressure being applied to your body, so why does the squeeze stop?

It stops because it's due to the reasons about which I was speaking in my V-Y-T-shaped ridges post.

 

[Soggy]

An additional point to consider (because this thread hasn't gone on quite long enough):
Why do you feel squeeze in a drysuit without sufficient air in it, but don't feel the squeeze when air is added? Adding air to the suit isn't going to decrease the pressure being applied to your body, so why does the squeeze stop?

VOLUME VOLUME VOLUME. You are inside a balloon. The BALLOON IS SQUEEZING YOU. If there is not sufficient gas volume in the balloon to keep the balloon larger than the space you are occupying the BALLOON will squeeze you. It isn't about the pressure the gas/water is exerting on you, it's about the suit becoming too small for you.

Think of it like the event horizon in a black hole if you are inclined towards astrophysics.

 

[ClayJar]

VOLUME VOLUME VOLUME. You are inside a balloon. The BALLOON IS SQUEEZING YOU. If there is not sufficient gas volume in the balloon to keep the balloon larger than the space you are occupying the BALLOON will squeeze you. It isn't about the pressure the gas/water is exerting on you, it's about the suit being too small for you.

I believe what you're trying to get across is that modelling it as a spherical diver in the concentrically spherical drysuit breaks down in practice, but you're being taken as arguing within that metaphor. The facts of drysuit squeeze are that it is the practical reality that the available air and drysuit material are not capable of remaining evenly distributed around the diver's body, and it is that uneven distribution that manifests as squeeze.

 

[Soggy]

I believe what you're trying to get across is that modelling it as a spherical diver in the concentrically spherical drysuit breaks down in practice, but you're being taken as arguing within that metaphor. The facts of drysuit squeeze are that it is the practical reality that the available air and drysuit material are not capable of remaining evenly distributed around the diver's body, and it is that uneven distribution that manifests as squeeze.

What I'm trying to say is that the space within the non-elastic, non stretchable suit is forced to shrink in volume because the volume of gas inside it is reduced due to increased pressure and you are in the way of that shrinkage, thus the suit squishes you.

 

[ClayJar]

What I'm trying to say is that the space within the non-elastic, non stretchable suit is forced to shrink in volume because the volume of gas inside it is reduced due to increased pressure and you are in the way of that shrinkage, thus the suit squishes you.

So, the key there would be that you are in the way of the *shrinkage*, not that you are necessarily in the way of the suit. I believe that would work without conflicting with the mechanism of squeezing, if it would work with what you're saying.

By the way, for anyone who hasn't experienced one, a constrictor-style squeeze (like the kind that can make it feel hard to breathe) feels like someone's pulled the suit taut across your chest. It's not the feeling of someone sitting on your chest -- it's the feeling of someone grabbing the back of your shirt and twisting it into a ball until the shirt fabric starts constricting you.

 

[Soggy]

So, the key there would be that you are in the way of the *shrinkage*, not that you are necessarily in the way of the suit. I believe that would work without conflicting with the mechanism of squeezing, if it would work with what you're saying.

I guess. The suit is getting smaller. You are not. Thus spake squishathustra.

 

[markr]

VOLUME VOLUME VOLUME. You are inside a balloon. The BALLOON IS SQUEEZING YOU. If there is not sufficient gas volume in the balloon to keep the balloon larger than the space you are occupying the BALLOON will squeeze you. It isn't about the pressure the gas/water is exerting on you, it's about the suit becoming too small for you.

Think of it like the event horizon in a black hole if you are inclined towards astrophysics.

The balloon is not squeezing you, the pressure outside the balloon is squeezing you. The suit doesn't become to small, it is being pushed in by the external pressure or are you claiming that the suit is subject to some form of space/time anomoly which causes an extra large to become a medium at depth?

As far as the black hole, it's an entirely inaccurate analogy. The force involved in a black hole is gravity not pressure. The gravitational force works on the individual atoms of your body with a force inversly proportional to the square of the distance from the black hole, pressure is applied to the surface area of your body. All of which has nothing to do with the discussion at hand.

 

[ClayJar]

The balloon is not squeezing you, the pressure outside the balloon is squeezing you. The suit doesn't become to small, it is being pushed in by the external pressure or are you claiming that the suit is subject to some form of space/time anomoly which causes an extra large to become a medium at depth?

GAAAAAAH!

Do you disagree with what I was trying to explain in post 77, or do you not understand it? There needn't be a space/time anomaly -- the fact that the material gets taken up by the ridges is elementary and trivially observable.

If some of the material gets taken up in the ridges, the effective "size" of the suit is indeed reduced.