Curious Question - Wave action compared to ATA

[scagrotto]

If there is "force," there is pressure (pressure is force per unit area).

Pressure is just the average of the force being applied by lots and lots of atoms or molecules slamming against something. In perfectly "still" air the molecules (the O2 and N2 are diatomic, which is why we refer to O2 instead of just O) are still moving quite fast at any temperature you're likely to experience. In the case of air rushing out of the 2nd stage the velocity of the air mass will add to the existing velocity of the molecules, causing them to impact with greater speed and impart more force. Pedantically that force will be pressure because it's exerted by a fluid, but I don't think it's quite right to say that particular force/area is because the air is still at a higher pressure as a result of the IP pushing it through the 2nd stage valve. YMMV if you think the ambient air pressure spikes up and down when you get hit by a gust of wind.

As for the pressure exerted by a passing wave, as explained above you won't experience a pressure increase anywhere near as great as caused by a column of water as high as the wave. I'm not sure that water behaves the same way, but the load exerted on soil by the posts of your porch or deck spreads out at a 45º angle. If your post exerts a force of 1000 pounds per square foot the soil immediately under the post needs to resist that much force. A foot below the post it would be something less than half as much. That 45º spreading seems to fit well with the exponential decrease mentioned by Tursiops.

I asked a related question a long time ago: If you dive down to, say, 100' inside a tube (that you can just fit into), is the pressure on you the same or less than if you were at 100' in open water? The reply was that it is the same, because the only water that affects you pressure-wise is that which is exactly above you. I assume that is correct.

In theory I'm pretty sure that the tube could have a cross section immediately above you that's got a diameter only slightly larger then a molecule of water because that's enough for the molecule to transmit the pressure from the molecules above it. In practice the cross section would have to be big enough that it does nothing to slows any molecules passing through it, but 1/16" in diameter should certainly do the trick. The discussion about waves should make it clear that it's not just water that's directly above you, or the wave crests would have no effect when you're directly below the trough.

 

[Subcooled]

Has anyone dived in three feet waves to a depth of 90ft?

Does that lead to a fluctuation of 0.1 bar / 1m / 3ft in depth when you have reached the bottom at 90ft? Yes? No?

 

[tursiops]

Has anyone dived in three feet waves to a depth of 90ft?

Does that lead to a fluctuation of 0.1 bar / 1m / 3ft in depth when you have reached the bottom at 90ft? Yes? No?

Yes, No.

it also depends on the water depth; surface waves in shallow water (i.e., depths comparable to the wave's wavelength) behave differently with respect to pressure fluctuations fall-off with depth.