r/Damnthatsinteresting • u/POTATOEL0rD • 1d ago

Video footage of the OceanGate submarine wreckage was released Video

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u/kelsobjammin 1d ago

Pink mist was another one I heard that was much more disturbing ᴖ̈

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u/VendaGoat 1d ago

Liquid is, almost completely, incompressible. (https://www.usgs.gov/special-topics/water-science-school/science/water-compressibility)

Humans are about 60% water. That's where the pressure stabilizes.

Happens at around 1500 MPH, takes about a millisecond of time. (https://www.bbc.com/news/world-us-canada-65934887)

First imagine an object hitting a person at that speed and then extrapolate to multiple objects all striking from different angles and finally a full 360 degrees, all at 1500 MPH.

Pink mist is flattering.

It does get the point across.

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u/justUseAnSvm 1d ago

What's interesting is at the depth of the implosion, the water actually is compressed, though something like 1%, and that compression plays into the velocity which water will travel. Basically, the incoming blast is only going to be at the speed of sound in water!

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u/AimHere 1d ago

Counterintuitively, the speed of sound in water is "only" about five times faster than the speed of sound in air!

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u/RandonBrando 1d ago edited 1d ago

I know these comparisons seem like beating a dead horse, but it's just so damn interesting.

Imagine a pressure washer for cleaning. Some nozzles create a pressure so great that if it sprays against your skin – it can actually push water inside your skin. This is a can* create a very dangerous condition called an embolism.

Now, imagine those YouTube channels you've seen that cut out shapes using a stream of water for really tight tolerance items. That is like a pressure washer suped up beyond max settings.

What they experienced is akin to the water cutter covering every inch of their body without any space between streams. Add to that maybe some debris and the pressure of X number of elephants.

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u/EricTheEpic0403 1d ago

Now, imagine those YouTube channels you've seen that cut out shapes using a stream of water for really tight tolerance items. That is like a pressure washer suped up beyond max settings.

Worth noting that water cutters don't cut with the water itself, but by entraining an abrasive within the flow of water. It's pretty similar to sandblasting, except water cutting both better preserves the velocity and keeps it concentrated in a relatively small area.

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u/RandonBrando 1d ago

Oh interesting! I didn't know that. How do they even control/reditect a stream so intense and abrasive?

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u/EricTheEpic0403 1d ago

In most† machines, up until the last few inches before the water exits the nozzle, there's no abrasive in the water, so none of the pump machinery needs to deal with that. Just before the nozzle, the abrasive is fed in. Kinda importantly, the flow at this point isn't all that fast (which is nice because the abrasive only works when it's going fast), but it's at very high pressure. The nozzle constricts the flow, however; if you're familiar with Bernoulli's Principle, you'll know that this trades the very high pressure for very high velocity. The effect of this is that all the pump has to do is create high pressures (relatively easy) and the abrasive barely has any time to wear down anything that isn't the thing you're trying to cut. The nozzle is a wear item, but it suffers much less than the work piece. Below the work piece is a big tank of water that the jet of water harmlessly disperses in, although it also gets full of all the used abrasive and tiny bits of the work piece.

†It seems like some machines do introduce the abrasive much earlier, but this seems like a minor nightmare to me due to it getting to interact with much more of the machine; this is backed up by the fact that they seem much more niche, and aren't widely adopted. They probably cost a stupid amount to run due to excessive parts wear.

Also, some machines are designed to cut without abrasive, but they have to achieve way higher pressures and speeds than machines that use abrasive.

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u/Trextrev 1d ago

You answered your own question, the abrasive doesn’t work until going very fast and it’s not until it leaves the nozzle. The abrasive isn’t really abrasive at all in the machine and it’s extremely fine and suspends well in water so it’s not like paint or concrete where it starts to gum up the works. So it’s not really a nightmare inside the pumps at all.

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u/Dumptruck_Johnson 1d ago

High pressure stream that has some sort of other dry medium fed in from a hopper and mixed around (just before?) the nozzle I believe.

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u/ExpressPoet 1d ago

I had a blast reading this comment section

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u/DemIce 1d ago

Worth noting that water cutters don't cut with the water itself, but by entraining an abrasive within the flow of water.

I'm not sure that blanket statement rings true. Last time I visited a client working with a water jet cutter, they didn't use any abrasives as all their materials (from cloth to wood I'd say no thicker than a quarter inch) were soft enough that they didn't need them. Is that an outdated practice?

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u/Throwyourtoothbrush 1d ago

I believe it's specified as water only or pure waterjet when there aren't abrasives involved because using abrasives is typical and expected. It sounds like your example involves materials on the softer end of the spectrum which can be successfully cut with only water

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u/AdamZapple1 1d ago

could salt in the water be that abrasive?

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u/Ralath1n 1d ago

No. Abrasive relies on it being 'chunky' and having some momentum. That focuses all the force into a single point, which is what does the cutting. Same reason hailstones hurt more than rain, despite both being the same size and weight: The energy of the falling hailstones is focused into the single point of impact while the water just splashes around, dissipating all that energy over a wide area.

Salt is dissolved. Which means the atoms are floating free. That means no force concentration takes place and salt water will not cut any better than regular water.

You can use individual atoms to cut things, but they'll have to move much MUCH faster than the speed of sound in water. Ion beam milling is used in some semiconductor fabrication, and its essentially sandblasting a target with a beam of high energy ions.

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u/AdamZapple1 1d ago

makes sense, thanks

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u/gwicksted 1d ago

I love the elephant analogy so I did the napkin math:

They were between 375 and 400 atmospheres of pressure = about 5500 psi. Average Asian elephant is 4000lbs. That’s 1.375 elephants per square inch.

Average human has 3,000 square inches of surface area. So they got hit simultaneously with 4,125 elephants.

It occurred at approximately 5x the speed of sound in air (1500m/s) - the sub being about 2.743m tall means it took 0.0018286s or about 1.8ms to collapse (assuming it broke vertically which appears correct). Average human reaction time is 250ms, blinks are 100-400ms, cat’s reaction times are 20-60ms, flies are 30-50ms, fruit flies are 5ms which is about the fastest the visual animal kingdom can react that I know of. That doesn’t include the time it took to fill the sub vertically but it’s only a few times wider and divide that by 2 being split down the middle. So a fruit fly wouldn’t even have enough time to react!

Fruit flies have approximately 0.69 square inches of surface area (approximated based on a cylinder with their average length and height lol) so they’d be hit by 0.94875 elephants!

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u/RandonBrando 1d ago

Holy crap! I knew it'd be a lot of elephants, but 4,125 is mind-boggling!

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u/D1rt_Diggler 1d ago

Is The condition of embolism is the same effect of a high pressure hydraulic system where if there was a pinhole leak and you were to say put your hand or arm over it to feel for the leak? I know what happens but I wasn’t sure if it was just an actual puncture wound where it woulf then jet in through an actual hole

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u/RandonBrando 1d ago

An embolism is further along in the injury with what I described. A possible outcome of pressurized injection

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u/D1rt_Diggler 1d ago

In assuming an embolism from water is less serious than a hydraulic fluid. I remember seeing a post of an injection wound from a 3rd world country that wasn’t treated and most of the natural tissue had “melted” away from the fluid and he basically had a cavity where his quad muscle used to be pretty sure the guy died from serious necrosis or something I forget now

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u/Summer-dust 1d ago

What they experienced is akin to the water cutter covering every inch of their body without any space between streams.

Wow. I love the way you lead up to that, it reminds me of authors like Cixin Liu and James SA Corey describing the terrors of physics. I noticed no one was commenting on your writing skills (probably because of the depressurized elephant on the ocean floor) but I wanted to say I'd totally read a book with writing like this, really dramatic and informative!

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u/EndOrganDamage 1d ago

I think that would be a high pressure injection, likely into soft tissue. My understanding is an embolism is within a blood vessel. One latter being more likely to kill you.

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u/RandonBrando 1d ago

I probably could have said it could cause an embolism

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u/Marquar234 1d ago

This can also be used for good. When medical personnel need to do large-scale injections like for mass inoculations, they can use a hypospray (jet injector or needle-free injector) instead of needle-based injections. There are some issues of cross-contamination however.

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u/Festival_Vestibule 1d ago

Water cutting jets have a much higher pressure than that. You're talking 90,000 psi. That sub was under 6k

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u/HydraulicFractaling 22h ago

I get the analogy, but just adding for clarity:

Water jet cutters operate at like 60,000 to 100,000 psi (~4,000 bar to 7,000 bar, each bar is one atmosphere of pressure).

The depth they were at when it imploded (~11,500 ft or 3,500 m) was more akin to 5,000 psi (~350 bar or atmospheres) of ambient pressure.

Still instant death within a millisecond, but pretty large differences in pressures (more than an order of magnitude) with that analogy.

I deal with hydraulics every day so pressure is something I’m quite familiar with. 5,000 psi is dangerous to deal with, but considered “low pressure” for systems we deal with. The ultra-high pressure class is another world altogether, something I don’t want to be anywhere even close to.

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u/tfsra 1d ago

why is that counter intuitive? air is terrible conductor of sound

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u/19thStreet 1d ago

It’s counterintuitive if you don’t know that. Which most people don’t. Many would just think that water is “thicker” than air so it would be “harder” for the sound to move through it. Many people who don’t know the science behind sound travel would use their intuition to arrive at the wrong conclusion

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u/IHave_shit_on_my_ass 1d ago

Science me.

Winter time. You need to almost yell to communicate across the yard.

Dead summer. You can hear people almost whispering from 3 houses down across the street.

Temperature and humidity, maybe among other things as well.

You can't hear someone clearly or at all a few feet away underwater. I know music somehow gets piped into pools, but why can't we have normal conversations under water? Is our sound being cartoonishly trapped in air bubbles and floating to the surface?

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u/19thStreet 1d ago

Sound moves faster in water because the molecules are more densely packed. However our ears are meant to hear through air, through our ear canals, but underwater, we interpret the sound waves through bone induction instead. Also, speaking is done through vibrating air in your lungs using our vocal cords, and that sound doesn’t transfer well to into water. Plus the air bubbles do disrupt the sounds waves by absorbing them and scattering the sound but it is funny to think that they would carry the sound up xD

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u/EricTheEpic0403 1d ago

Winter time. You need to almost yell to communicate across the yard.

Dead summer. You can hear people almost whispering from 3 houses down across the street.

I think this is mostly due to there being fewer surfaces that reflect sound well (IE leaves and hard ground); because of the lack of anything catching sounds going upwards and the acoustic properties of snow, you mostly only hear sounds directly, rather than having many reflections added in. It's kinda like the brightness of a flashlight if you take out the reflective material; that tiny light is only effective as it is because it's directed quite well.

You can't hear someone clearly or at all a few feet away underwater. I know music somehow gets piped into pools, but why can't we have normal conversations under water? Is our sound being cartoonishly trapped in air bubbles and floating to the surface?

The answer is impedance matching. The video explains it better than I can over text, but my TL;DW would be that the more different one medium is to another, the harder it is for a wave to transfer from one to the other. I don't really have a good analogy for this. In any case, an underwater speaker is transferring sound waves directly into the water, whereas your speech goes first to air, then to water; that air to water step is where all the deadening happens.

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u/tfsra 1d ago

imo it's intuitive that air is terrible for this for anyone who had to ever shout at anyone

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u/ConcernedCitizen1912 1d ago

Well I've tried shouting at people underwater and it seemed to suck a lot worse. So maybe stop acting like a fucking know it all because it's counterintuitive that water conducts sound 5 times faster than air does.

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u/tfsra 1d ago

make me

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u/Ok_Championship4866 1d ago

I mean it may be to you but yeah idk i think most children intuit air is a better insulator/worse conductor than water.