I am a drilling engineer, we have to get certified in well control before doing any operations. This one is a huge topic.

A good analogy is to think about standing on a spring, compressing it. You are pressing downward with exactly your weight, and the spring is holding you up. Place a ceiling directly above your head, so your head is almost touching it. Now step off the spring, and you're still pushing against the ground with exactly your weight, same as before. And now, to simulate the pressurized air being at the top of the tube, we put the spring on your head. The spring isn't compressed by your weight anymore, so it expands and presses against the ceiling, and thus pushes down on you. So now you're pushing against the ground with your weight PLUS the force of the spring pushing you downward by trying to expand against the ceiling.

Old oil and gas guy here. I remember leaning this in one of the countless hours of training and education that we had to maintain to keep our field certs. I was in frac, and we didn’t have to worry so much about gas bubbles in the day to day pumping operations in the formations we were pumping into. We just needed to be aware of such phenomenon. Thanks for reminding me of it!

Another way to think about this: When the water is above the air, gravity is pulling the water down onto the air, which exerts a compression force which is opposite to the pressure of the air pushing outwards. Therefore, part of the air's pressure is being counteracted by gravity, and the total net force from the air's pressure is reduced by that amount. When the water is on the bottom, its gravity is no longer trying to compress the air, so there is no force to counteract the outward air pressure, so the pressure it exerts on the _container_ becomes higher. It is very counterintuitive, though..

This is a really well established fact for any petroleum engineer because the well can receive a gas influx from the formation that we call "gas kick", this gas rises up the well which ((increases)) the pressure on the bottom formation which can cause it to fracture, so the most dangerous kick is the gas kick.

The thumbnail, which was at one point also part of the video (3:20) suggests, that it isn't a closed system which is confusing. Without the closed top I would even expect the pressure to decrease.

I like that you put several seconds of black screen at the end so that the automatic video suggestions don't block anything important.

That is very counterintuitive but with the spring example, it makes sense!

I found the correct answer with a slight variation of the reasoning of the video: as the air goes up, it "should" undergo an expansion because it "should" be subject to a pressure decrease. But the volume being fixed, the expansion is constrained: the pressure of the air stays the same: the intuition that the pressure doesn't change is correct, but it applies to the air, not to the whole system. Therefore, with the same pressure of air, the pressure at the bottom is higher when the air is at the top because you have to include the weight of the long column, while the initial situation only had a small water column added to the air pressure.

My brain wasn't registering that the tube was completely sealed. Which means now we need to see this with the top end open.

I’m a scuba diver. And with my experience and with playing with soda bottles sealed and un sealed bottles. So I knew there would be a change in pressure. Great job. Thank you 😊

This is one of your best videos. Surprising result, great series of experiments, thorough explanation of what's going on.

Glad to have got it wrong in exactly the same way you did haha.

Yup. I got it wrong.

Indeed, for a vertical pipe, the gravitational potential energy of the water changes. However, for the U-shaped tube, it is not true! The water also raises on the other side! The problem can not be treated by neglecting the process and just looking at the initial and final states. The process of the bubble rising is quite rapid and far from being quasi-static (not only the gas doesn't travel in one piece, but the rise of the tiny bubbles it splits into is accelerated), so basic thermodynamics doesn't work well either (i.e. the law pV/T= const for the gas is valid only for quasi-static processes). The gas, however, heats up while being pushed up by the liquid's pressure (work is definitely being done on it), and this increases its pressure (just not proportionally, since the process is not quasi-static). Why does the liquid remain at higher pressure after the thermal equilibrium with the room (if that even happens, since, as you mentioned, the pipe could even burst from the high pressure) is probably somewhat ansewrable by non-equilibrium thermodynamics. One other factor to take into account is the work you yourself are doing to turn the tube back and forth.

Thank you for including multiple different explanations, only the high-pressure bubble diagram made intuitive sense to me but I know that others will have found the other explanations more helpful.

I was very surprised. I thought the pressure would stay the same since it's a sealed system.

I love how this channel has grown over the years and now is my favorite go-to place for science related videos on youtube.

I love that videos about fluid dynamics are getting more out there. I don't feel so alone as a fluid dynamics eng. student. Pressure systems are so wild!

The movement of the gravitational potential energy was the key for me in fixing this concept in my mind. Great examples to facilitate comprehension. Thanks.

That L shaped thing in the thumbnail doesn't look like a sealed system.

It's one of those problems where once you know the answer, it seems so obvious but until then, it's anything but. Great content!

I too was surprised, l thought the pressure would be greater with the bubble on the bottom due to the increased water column hight. I didn't even think of the air as a spring. Great video as always.

I've seen a few of your videos/shorts and thought they were interesting, but this one made me subscribe. Great job explaining a very non intuitive concept!

And that bubble pressure increase was then probably also the reason for the oil rig explosion in some video I cannot locate anymore, where they are drilling the hole and suddenly they scream they hit an unexpected gas pocket and need to abandon the area, seconds later greyish-brown thick liquid erupts from the hole and covers the whole area, including a nearby city. Or was that one of my strange dreams many years back that I now falsely assume having been a video? I even remember clearly how some of the shots in the video looked, for example a street light next to a low, white wall in the dark under a tree in the rain.

I would say it increases. Water is incompressible so its volume is fixed, and therefore the volume of the gas is fixed too. Assuming that the temperature of the gas is fixed as well, then so will be its pressure. So when the gas is moved to the top, it pushes on the water below it with the same pressure it had at the bottom, so the extra water column remaining will increase the pressure at the bottom.

Very educational! I love the fact that you asked very intelligent questions, one in particular that I didn’t think of but realized that it was an excellent question as soon as you said it. Where did the extra energy come from? Excellent observation when he mentioned the center of gravity lowered

This was fascinating dude! Seems so simple, yet profound!

5:47 Jail Speedrun Any% 💀

Loved what you said in the end. Those counterintuitive phenomena let you learn and understand the fundamentals better

Been subscribed for a while but this is one of the most fascinating of your videos I've seen. 👍

Wow that’s so interesting! It was completely wrong with what I thought. This type of physics is truly incredible!

According to the formulas: Case 1: When the bubble is at the bottom Its P = h*d*g ; h= height of vessels or tube, d= density of liquid, g means gravity When the "air bubble" gets on top the pressure becomes P = P(atmosphere) + h*d*g

That has got to be your best video yet. That is a huge lesson. Now I have to configure my brain to get used to that kind of thinking.

Thanks, impressive with your investigation. Good luck with Open Sauce

I was still telling my TV that the pressure shouldn't change, until you pointed out the shifted center of gravity.

Damn, that really was surprising, but very cool

I was able to reason out the conversation of PE to KE but still ended up thinking that the pressure might drop. Actually at first i thought it might stay the same, if all of the KE was used to do the work of pushing the bubble to the top... But i thought maybe some if that energy is imparted to the walls of the container, converted to thermal and then lost through conduction. But that might violate the closed system on its own... And honestly that physical model you built helped so much in demonstrating whats really happening. I loved this!

Also without the bubble at the top, the surface tension of the water will prevent the water from falling (even if the other side is open-ended), that is off-loading the weight of the water to the tube itself, causes a decrease in water pressure overall.

Pressure in a sealed vessel is potential energy, so you’re converting types of potential energy

Without the water weight on top to compress it, the air expands. The volume of the tube is fixed, but the air expands as it rises. So the system pressure overall goes up to compensate for the air taking up more space

I was really confused by this. And then the moment you introduced the spring "Because the air is springy" it instantly clicked. Perfect illustration!

Wow !!! I so didn’t expect nor indeed predict the effect once you’d stated the question. Awesome !!!

Conservation of energy - when the water is at the top, the gravitational potential energy is higher so the pressure potential energy must be lower, and vice versa

I got confused because I assumed that the tube was open. the first diagram he shows also has open containers. with an open tube the pressure would decrease, because when the air would reach the top it would be able to disperse.

Never thought of this problem before until I saw this video. Great topic.

I don’t comment much after watching your videos but most of the time, the experiment looks so simple it looks kind of silly. When watched until the end, it blows my mind. Genius content! ❤❤❤❤❤

When the air goes up the potential gravitational energy decreases so the energy stored by the pressure differential increases.

Before this goes to far im going to say it increases becasue the air acts like a shock absorber. Edit: i was a plumber for a very long yime and also dabnle in hydrologics

I understood it, when you explained it with the transformation of potential energy into pressure @8:20 . A very interesting problem. Thank you.

GREAT LESSON!! I will not forget this lesson because if the creative way you taught it! Thank you!

Should have anticipated it since you were at less than 1atm when the bubble was at the bottom. You made the system with the bubble at the top (1atm) then sealed it and flipped it over (0.9atm). But I too got it wrong. Thought it would go down.

[0:53] "Right now we're at 0.89 bars" That *gives away the answer,* and confirmed that my guess was correct. The only way the pressure could be that low is if the air was acting as a cushion.

I paused and reasoned exactly like you did, the pressure stays the same but i wouldnt be surprised if it decreased. Very surprising result though and i loved your explanation, thanks for making these videos!

Good observation - quite counterintuitive. I came to understand it by thinking the bubble to be equivalent in weight to the water column it supports, at equilibrium. The part about energy being converted to pressure seems incorrect - the energy is dissipated when the water trickling through the bubble settles. Analogously, the potential energy of the spring doesn't change.

Okay so a co-worker of mine is 100% convinced this is wrong. His reason is that because the rigidity of the tube causes a vacuum to suspend the water at the stopper at the top causing negative pressure at the top which reduces your overall pressure at the bottom.

Without the water weight on top to compress it, the air expands. The volume of the tube is fixed, but the air expands as it rises. So the system pressure overall goes up to compensate for the air taking up more space.

I loved this. I decided that the pressure would stay the same. But then an experiment let us throw that hypothesis away and consider what other variables there are such as the effect of elastic potential energy and gravitational potential energy in transferring energy into or out of the system to change pressure. A cool problem!

Hey James, I noticed you’re using a Keller pressure gauge in your setup. I work with STS Sensor Technik Sirnach, where we specialize in piezoresistive transmitters that are known for their reliability and precision. If you ever face any challenges with your current gauge or are looking for an alternative, I’d be happy to help you explore some options that might better suit your needs. Keep up the great work on your videos!

There is a fault in the premiss. You in no way stated that the air bubble introduced into the system, was under pressure. You created the assumption that the system was first created with the bubble at the top, where it was not under pressure, and caused the bubble to move to the lower position. Under that circumstance, there is no pressure when the bubble is at the top, thus you failed to provide the exact circumstances under which the bubble was created.

feel really sad that such Informative channels have low subscribers where a random mf doing stupid things on social media have more subs😢

That is such an awesome demonstration, and while it goes against initial intuition, it makes sense mechanically.

Very insightful and a nice discussion of a counterintuitive setup.

A great demonstration on the different behaviors of compressible and in-compressible fluids. Should be done in every undergraduate physics lab.

I also thought it would stay the same. This was fascinating, and despite being a degreed engineer, I learned something today! Awesome video!

Fantastic, one of the most interesting videos I've ever watched from you.

Loved this one. Great video. Thanks!

Thanks for your fantastic demonstration! I wish I had someone like you teaching physics in college. I struggled to all math related courses even with private tutoring. What amazed my professors was that I could look at a circuit, be it electric, hydraulic or mechanical, I could choose the right answer from just looking at a diagram or circuit, but I could not explain why I chose that when it came to math. Some suspected I was cheating, always picking the correct option, but at that time, in the 1970’s we had to explain our choice by long hand writing how we came to the choice we had made. Studied all the laws but could not quote them verbatim. I was called to one of the professor’s office where he asked me to select the correct answer to experiments such as you did. I came out with the correct answer all the time. Once he was certain I was not cheating, he asked jokingly “are you psychic?” . I answered, “ I don’t think so, when looking at a setup like yours, it JUST MADE SENSE TO ME” but I was unable to, explain it in terms of physics laws. I was told that he could not give me a passing grade without an appropriate answer. Therefore the tutoring. I knew I would never male it as a physicist, my first choice. I chose biology as a major, and passed. Went on to medical school and excelled in my class graduating with the second highest GPA. I went on to work at Ivy League medical centers. My favorite subspecialty within medicine is Apheresis and dialysis. Dealing with osmolarity, intravascular, extravascular spaces, and “third space” (neither intravascular or extravascular, but rather “in between”. The difference is that if one chooses the wrong fluid for replacing what we are taking out the patient will die. In a 42 year career, none of the patients undergoing in massive fluid or cellular depletion , have died! aAplication of affinity columns in vivo as part of a circuit, the answer is crystal clear in my mind, but I CaNNOT EXPLAIN WHY! I invented several new instrument circuits which are FDA approved. I NEVER GOT A PENNY for my inventions, I give the credit to the engineers / physicists who came up with the formulas that describe the efficacy and mode of operation of these hydraulic and osmotic altering circuits. I am now 70 years old. I have one more “great idea” for yet another modification of an existing circuit that would allow us to separate different types of white cells, while in a continuous flow centrifuge. This would be able do decrease the duration of stem cell collection significantly. Unfortunately, my current employer is absolutely not interested in my ideas. I would gladly give you my hand drawn schematics so you can bring it to market. I am at a point in my personal life, I have pretty much given up on a lot of things, due to my wife profound depression and panic attacks which consume most of my salary and my time. 😊I am not allowed “research time” I had while at Mayo Clinic. Unfortunately, I left Mayo 10,years ago. I am now at a franchise of a major Cancer center. Unfortunately, all they are interested in is money and I have absolutely no support for research. Actually, I wouldn’t even call it research, it is the use of existing devices applied towards a different goal. All the best IV -VIII- O - II- IX- IX, IX. IX VIII IV anytime

Great video! Increase was dead on my decision tree but it makes so much sense now.

Same reasoning here. First, about staying the same in a sealed environment, then decreasing as there would be a lesser water column

I feel like imagining the atmosphere as though it were a liquid such as the ocean helps to illustrate how and where pressure is applied or relieved in this instance

This is my exact question. Thank you for answering!

It makes sense if you think of it in terms of total energy. The configurations with the bubble at the bottom has an higher potential energy than the configuration with the bubble at the top (it's easy to say as the second configuration is more stable, hence it has a lower potential energy). Moving from a configuration with a higher potential energy to one with a lower potential energy, that energy has to transform into something. That something can only be pressure (yes, pressure has the same unit as energy)

As a experienced scuba instructor I was surprised too and even more surprisingly I had the same reasoning as you in the beginning and I too got it wrong

I guessed that the pressure would decrease. This was a superb analysis!

Amazing video. I predicted the pressure would decrease since the hydrostatic pressure is just a function of h... except that assumes atmospheric pressure at the top of the water column. I think a good way to sum up the confusion is that this problem superficially resembles another common problem (your conventional ρgh problem), but it differs in terms of which assumptions are valid.

Amazing and mind blowing experiment. Please repeat the experiment with 1 gauge at bottom and 1 gauge at top to see both at same time... It would be interesting to see the result.

The example with the spring immediately made me understand why it works the opposite way I naively thought it would.

What an intriguing physics problem! It's fascinating how the pressure actually increases as the air pocket rises to the top, defying intuition. This experiment underscores the importance of hands-on exploration and thinking outside the box in understanding complex phenomena. 🤯

I know this from working in the automotive brake industry. A small amount of air in a brake line could dramatically affect the stopping distance ( by several feet). So your stopping force is proportional to the pressure applied, (for tmoc system actually a lot more force than the applied pressure, but at a certain point you get to the knee point and it eventually becomes 1-1 input to output force). Having to bleed brake systems for basically a cubic millimeter of air is very annoying depending on the type/design of the calipers. Some types seem to be prone to getting air stuck. Thats why straight off the assembly line usually has the best brake performance due to manufacturers using a push/pull method to fill the brake line when the system started off dry. That is usually better at getting any air out of the system.

Air in a sealed system created a kind of shock at the bottom. You can see the pressure go up until it is 100% out of the liquid. Brake systems work that way also.

Great Video! I thought the pressure might increase due to the better compressability of the air bubble. But it was for the wrong reason and I never expected it to have a significant effect. I thought about the atmospheric pressure compressing the air a little less when it‘s higher up - atmospheric pressure decreases with height. but that would‘ve been tiny and I disgarded it. It‘s a great help to think about the potential energy due to the shifting center of gravity. And then energy conservation does the trick. Still bothers me that I almost had the right answer for the wrong reasons 😂

This was really interesting, my initial answer was to decrease since the column of liquid would be shorter, hence pressure should decrease. however thinking about the gas equation made it make sense. thank you for such an interesting video

Very Nice question and Nice explanation man❤

I would say it goes up. The air pocket is the highest pressure area (it pushes the water away), by putting the high pressure on top of the vertical column of water it is working together with gravity to push down as opposed to against gravity when it is at the bottom.

My goodness, not even the simple looking things are simple 😞 I need to rehash my science understanding. Very humbling!

Your Channel reminds me why i loved physics class in school. The mankind of the 21st century will need guys like you to keep them hungry for knowledge :)

I had it in my head that the bubble would try to expand, but that it couldn't in a sealed tube, so the pressure couldn't change even though it should. It's pretty awesome to know the measurable truth of the physics behind it.

You've highlighted why you should never have any air in your brake system or any closed fluid system - Very good presentation

Its interesting from another perspective as well - and that perspective is statistical mechanics. Basically the potential energy is getting converted to "pressure" as he says - but the kinetic theory of gases really tells us that pressure is going to amount to a higher velocity for rhe molecules of water, which in turn means that initialy potential energy stored in the bubble got converted into kinetic energy of the molecules.

The fact that the air bubble moved upwards on its own when the "tail" was deformed has clued me in that the potential energy change might be the solution here. Great demonstration!

I hadn't heard of this before but it makes sense that the bubble when it was at the bottom would have had more water weighing down on it - it would have been somewhat compressed whereas the bubble at the top would have been somewhat rarified to compensate.

This shows again that analyzing a system by looking at its energy can help quite a lot in providing the right answer.

First the air reaches just the pressure required to compensate it's own height of water *at that depth*, and then, as it's volume can't change, it'll keep it's pressure. So now it's pressure will be *added* to that of the left column, where it *overcompensates* the pressure of that height of water at that (0) depth, now missing.

Preasure to be measured in the region of air and not liquid region, minor drop in preasure when the bubble passes the preasure gauge

The explanation using the hydraulic system was pretry much easier to understand than that using the mass spring system.

This is legit one of the coolest mathematical physics phenomena I have seen you talk about yet. Bravo!

Wow, it looks like every content creator I follow is going to be at Open Sauce. Sounds like a great conference.

I think it will increase because the pressure of the gas at the end of the column is strong enough to counteract the hydrostatic pressure developed due to the height of the liquid. When the gas moved upward the tube, its pressure stayed the same as its temperature, volume (incompressibility of water) and number of moles stayed constant however the new pressure developed below the column is now equal to the sum of the initial pressure of the trapped gas at the top and the hydrostatic pressure from the liquid column below it.