The Question That Everyone Gets Wrong (Including Me)
Vložit
- čas přidán 25. 04. 2024
- Checkout our sponsor, BetterHelp, for 10% off your first month: www.BetterHelp.com/actionlab
I will be at Open Sauce The 14th-16th of June!
opensauce.com/
Paper describing this effect in detail: iopscience.iop.org/article/10...
Shop the Action Lab Science Gear here: theactionlab.com/
Checkout my experiment book: amzn.to/2Wf07x1
Twitter: / theactionlabman
Facebook: / theactionlabofficial
Instagram: / therealactionlab
Snap: / 426771378288640
Tik Tok: / theactionlabshorts - Věda a technologie
I am a drilling engineer, we have to get certified in well control before doing any operations. This one is a huge topic.
Could you explain in a different way what is causing the overall pressure increase?
I have a hard time getting unconfused with the explanation given in the video and by some comments.
@@Yehan-xt7cw The air that's down there is pressurized to the same pressure that the column of water causes. That pressure doesn't disappear once it moves up, so it's as if you put a second column of water on top of the previous one.
Loosely speaking, when the bubble is down, the water pressure is fighting the air pressure. When the bubble is up, they're not fighting, they're cooperating.
If you stand on a pogo stick that's on a bathroom scale, the scale will measure just your and the stick weight, but the pogo stick is compressed enough to counteract your weight.
Now, lower your ceiling to the point that the ceiling is barely touching your head while you're on the pogo stick.
The force on the scale is equal to your weight + stick weight, force on the ceiling is zero.
If you now step on the scale yourself and wedge the pogo stick between you and the ceiling, the pogo stick will have to compress the same amount in order to fit, thus pushing the equivalent of your weight down on top of your head, and same force goes to the ceiling.
The scale is now measuring twice your weight + the stick weight, the ceiling now has one time your weight on it as a force equivalent.
@@therflash _" the water pressure is fighting the air pressure"_
That was the missing link. Now I'm getting it. 👍
@@therflash That was a really good explanation, thanks!
Does this have anything to do with pushing on the wall to make yourself weigh more when we were kids?
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.
????
do you think if you got a trampoline and then tightened the springs, so there was no spring force at all, the weight of the system would just magically change? I don't think so myself. Springs settle and they do not and cannot change the weight, no matter what. I could be wrong, but I don't think I am in this case.
@@deucedeuce1572 The point is that when the bubble is on the bottom, it's acting like a spring under your feet, while when the bubble is on top, it's acting like a spring on your head (the weight being negligible; just the springiness). You don't feel the pressure from the spring when it's under you any more than you feel the pressure from the ground. But if it's above you pushing down (off of the lid of the container), you feel the pressure of both the ground AND the spring pushing down on you.
@@stevenjones8575 For every action there's an equal and opposite reaction, is there not. If there is "X" amount of weight on the spring, then there is "X" amount of weight on the spring... and if the spring weighs "Z" amount of weight... the spring weighs "Z". If you weigh the man and the trampoline for example, it doesn't matter if there are springs on the trampoline or if the springs are replaced with an equal weight of non-stretching wire.
I could just be misunderstanding what he was saying... but I almost always know what he's talking about in his videos. Have spent most of my life studying all fields of science. I'm not usually one to misunderstand, especially when it comes to scientific "laws".
(As for equal and opposite reactions, if you have 10 pounds pushing on a spring, the spring is pushing back 10lbs. The spring will always compress to the exact weight to where it's pushing back on the object the exact same amount that the object is pushing on the spring. It matters not if it's a spring or a solid block of steel in that aspect. The force against each object is equal.
The force the trampoline has to exert to hold you up is equal to force it has to exert on the ground plus it's own weight. So in your example it's still equal
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..
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.
Well explained! That's how I reasoned as well.
That's a more intuitive explanation, I think. At least it clicks better with my brain. Top.
I was so close to getting it... I thought for sure the air pressure would decrease as it moved up, and I realized that it wouldn't be able to expand against the water. But I assumed the temperature of the air would decrease with the pressure decrease in a fixed volume
@@Zaros262 yeah I almost got confused about that too, but then I realized that the temperature variation only occurs if the volume can vary: it's the work of the pressure forces integrated on the volume variation. No volume variation = no work = no variation of T :)
Yep, this was also my reasoning, thanks for putting it into words!
By the way, @@renedekker9806 your Dutch is showing 😉, but I agree, this is a "top" explanation.
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.
Well I didn't think this would be true even for such small height
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.
That is very counterintuitive but with the spring example, it makes sense!
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.
Me too
Exactly, the moment he tried it with the closed tube I was like "woooh, that's completely different"
Yes, with an open top it's a simple hydrostatic pressure dependent only on depth.
This movie isn't acceptable
Posters who don't pay attention to such aspects should be condemned as scientists who are not good enough.
My brain wasn't registering that the tube was completely sealed. Which means now we need to see this with the top end open.
The thumbnail didn't really show it as closed. But the open tube case is easy as the pressure at the bottom of an open topped tube of incompressible fluid is always proportional to the height of the fluid column (in other words it goes down if open).
and if it were then the pressure would decrease instead - the top is at atmospheric pressure.
With sealed top, it's almost pipette, where bubble gives some freedom of movement...
I suspect the average pressure throughout the vessel does not change.
I think that his experiment doesn't match the question too. The jar in the question is not sealed.
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.
I like that you put several seconds of black screen at the end so that the automatic video suggestions don't block anything important.
I was very surprised. I thought the pressure would stay the same since it's a sealed system.
You also have to take into account gravity. If you removed gravity I wonder if it would stay the same 🤔
This is why education is important 🤦🏻♂️
@@ACatLoversHandle if you remove gravity, there's no such thing as top and bottom 😁
I think he bent the tubing out of its natural shape, which deformed the tubing and caused it to flatten, which increased the pressure inside. I think his entire explanation is wrong also... although I can't say 100%. I just don't think it works like that. As far as I know, a spring would settle with weight on it and would not, ever in any circumstance change the total weight/mass of a sealed system. Your car doesn't weigh less, because it's on shocks. I just don't believe that. If you change the shocks/springs with a steel rod that weighs exactly the same amount, your car would still weigh exactly the same if put on top of a scale in both configurations. Then if you filled the car with water and put an air balloon in the trunk or in the cab of the car, it wouldn't magically change the weight of the car (comparing the two configurations with water and balloons)... and/or if you tied the balloon to the floor of the car or let the balloon float to the top of the car. As long as the car, the water and the air all weigh the same and contain the same mass, the weight will stay the same (as far as I know). I hope you forgive the long explanation and repetition. It's not an easy thing to explain in just written words.
@@alexrvolt662 No gravity, no weight.
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.
nice, you nailed it.
Perfect!
what do you mean by extra water column? the height and amount of water is the same right, so i'm still confused how there is more pressure
edit: i get it now
Yup
From this result, I think it can be said that the bubble acts as a constant pressure regulator for the water which have the same height level.
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
Yes me too I also did the same!!! Are you a JEE aspirant?
Why p(atmosphere) if it is a sealed tube ?
The pressure of the bubble depends on the height of the water column when the tube was sealed, so it would be greater than atmospheric pressure. Pbubble=Patm+pghi.
The final pressure would be Patm+pgHi+pgHf.
So... P*2?
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 😊
Yup. I got it wrong.
Got it wrong too but I assumed the top was open to the atmosphere -so no spring.
No, WE got it wrong
@@ryanjohnson3615 ye dang
@Nulley0 implying that everyone got it wrong? I didn't.
The pressure is kinetic as increasing with the movement of water due to the influence of gravity, so the water has to stop at the bottom using its kinetic energy to form pressure from a vacuum
Glad to have got it wrong in exactly the same way you did haha.
Me too
28/4/2024 Sunday 8:56PM
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.
This is one of your best videos. Surprising result, great series of experiments, thorough explanation of what's going on.
I love how this channel has grown over the years and now is my favorite go-to place for science related videos on youtube.
Truee
Yeah, it's a great channel. I think he might be wrong about this experiment though. I can't say with absolute certainty. He probably knows more than me about this subject and other kinds of science... but at the same time, it don't mean he can't ever be wrong. I think the PVC systems pressure went up, because he changed the shape of the tubing and used force to do so. When the bottom was curved like in the first test, it was in it's natural resting state, which is the shape that it was manufactured to be in... but when he straightens it out, he not only has to use a certain amount of force to do that... but straightening the tubing causes it to flatten, because it's a tube being bent outside of its normal shape. For example, if you did the opposite and sealed off the ends of a perfectly straight copper tube then bend it, the pressure inside would increase in that case too.
@@deucedeuce1572 He returned the shape back. But pressure remained at higher value.
@@d4slaimless Good point. Appreciate the reply.
69-th like!
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!
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 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!
That L shaped thing in the thumbnail doesn't look like a sealed system.
Exactly. It looks like it is only sealed at the lower end.
That was my observation as well. If it is open to the air, the pressure is directly related to the height of the water column.
It looks like the blue stuff isn't fluid. probably just a solid model made for the visual
5:47 Jail Speedrun Any% 💀
"Hey Guuuys, look at this ODD little contraption I build."
?
I was really confused by this. And then the moment you introduced the spring "Because the air is springy" it instantly clicked. Perfect illustration!
The potential energy DOES NOT "convert" into pressure. The extra pressure is supplied by the stiffness of the tube from expansion when there's no water helping. It also doesn't work if the tall side is not capped, like what you've shown in the thumbnail
I was still telling my TV that the pressure shouldn't change, until you pointed out the shifted center of gravity.
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!
Wow that’s so interesting! It was completely wrong with what I thought. This type of physics is truly incredible!
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
The air can't expand since the system has fixed volume, and the water is incompressible. But that also means the air has a fixed pressure (since temperature and volume are fixed), thus the pressure has to increase from there as the depth of the water increases
The air could only expand if the tube is very soft material. But I don't think that's the case here.
Okay but your profile looks sus, the link has no content
I don't understand how no one is mentioning the Archimedean principle.
Water level higher = more pressure.
That should be the best explanation, no more theorizing required.
@@Broocklethe water level is lower and the pressure is higher.
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.
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!
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
But it could take or free energy to move the air from one place to the other...
When the air goes up the potential gravitational energy decreases so the energy stored by the pressure differential increases.
that's what he says in the video, but it's wrong. The pressure in the bubble stays the same, and the pressure change in water doesn't take energy.
@@deinauge7894 This here.
The potential energy goes into kinetic energy of the water passing the bubble, then into thermal energy of the water by viscous damping.
I was confused when he said the energy turned into pressure,
It's like saying that force of the magnet sticking to my fridge comes from magnetic energy@@deinauge7894
@@rainaldkoch9093this is the only explanation that makes sense to me. The pressure increases when the air bubble rises to the top because the gravitational potential energy of water molecules is getting converted to kinetic energy. Which implies that the temperature of the system must increase at least slightly to account for the increase in pressure. Since his set up is not truly "closed", in the sense that heat exchange will still occur between the contents of the tube and the surroundings, does this also mean that the pressure will eventually return to its original value once thermal equilibrium is achieved??
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
Fluid is incompressible, which is also like saying not expandable in a sealed tube with no bubble, so the fluid is holding itself up without increasing the pressure. When the bubble is at the top, the springiness allows water to fall more without holding itself up. I would bet a flexible sealed lid at the top would bend differently from holding the liquid alone as opposed to the bubble atop the liquid. The top lid is holding back the increased pressure that you expected.
Yes. This is confusing. The water a the top is like the the trick when you fill a glass of water and put a playing card on the bottom and flip it upside down. The water stays in the glass. The top of the glass pulls a vacuum. I suppose the vacuum goes down the water column to the playing card, where it equals the atmospheric pressure ... or whatever pressure the bubble would be set at. When you flip the system upside down, the water column has a base to stand at, so... This ok ?
Pressure in a sealed vessel is potential energy, so you’re converting types of potential energy
No, pressure can only do work if the volume changes.
Damn, that really was surprising, but very cool
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.
This was fascinating dude! Seems so simple, yet profound!
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.
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.
Interdesting 🤔
Partially correct. See my comment.
So does he mean there's something wrong with the test setup? Because we can see what the pressure gauge shows, and it's hard to argue against that with theory.
@@EPaulIII I can't find your comment you'll have to post it here.
@renxula yes that's correct, he is saying the test set-up is where the problem lies.
Another way to think about it as a sealed system: energy must be conserved, the water “dropping” (being displaced by air) decreases the gravitational potential energy of the system, so there must be an equivalent increase in energy of some aspect of the system in the form of a uniform pressure increase.
Edit: just finished the video and this is pretty much exactly the explanation used. Cool.
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)
[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.
My atmospheric pressure is only 0.82 bar where I live. Anyways you can't base it off the initial pressure because it depends on if you fill it with a bubble at the bottom or not and also the pressure increases slightly when you put on the cap.
@@TheActionLab okay, so maybe it wasn't the clue I thought. But I think the reasoning still holds. My idea of acting like a cushion doesn't seem much different than a spring.
Bad metaphor. If you replace that air with an exactly equal volume of water so that the entire tube was filled with water, you would have the same pressure. The compressibility of the air only matters when the air moves.
@@bovursine "Bad metaphor."
Maybe. It's not a good interpretation. But I wonder about your criticism. It seems to me that if you fill the tube with one fluid you negate the potential for the demonstrated change in pressure rendering the discussion moot. The difference in compressibility determines buoyancy and the trapped buoyancy is what reduces the pressure in the system isn't it?
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 get you said this before you watched the vid, but if the pressure on the air is increased then it puts more pressure on its container as well. It’s why a box container has weight pushing against its sides. So it would work as a shock absorber but it would apply some of that pressure onto its container. But part of it would just compress and not push against the side. Idk though that’s my guess. I’m just 15 so I don’t know a whole lot unlike you.
At the bottom the bubble is squeezed by the pressure in the tubing plus the weight of fluid.
At the top the bubble no longer has the weight of fluid on it.
The pressure of the gas bubble itself drops by the weight of the fluid, which means the gas tries to expand, which means the pressure at the top of the tube increases.
You'd expect pressure at the bottom of the tube to have dropped some as the fluid head has dropped but the only thing that will have dropped in pressure is the gas bubble.
Thanks, impressive with your investigation. Good luck with Open Sauce
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.
It doesn't matter. You can create the system by starting with the bubble at the top. You will reduce the pressure when you try to move it to the bottom. Potential Energy of the system is a state function.
We know that there is enough pressure to counter the weight of liquid, otherwise he couldn't have kept the bubble entirely on one side (we would have observed a bubble of vacuum on top in all cases).
I'm not sure why it would need to be stated that the air bubble is under pressure.
It's a closed system; the air bubble will always be under some amount of pressure. If it wasn't, it would be a vacuum.
You could even do it with oil instead of air.
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.
Been subscribed for a while but this is one of the most fascinating of your videos I've seen. 👍
Same reasoning here. First, about staying the same in a sealed environment, then decreasing as there would be a lesser water column
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.
best explanation possible imo, great job!
That is a really good explanation!
I bet this wouldn’t happen if you removed gravity though. Huh.
The only problem I have with this explanation is that the volume of water doesn't change either, so the volume of air should stay the same too.
I think I better watch the video again, and let it sink in for a while.
@@Yehan-xt7cw if you look in the video, the air does seem to occupy less space in the first position than on the second one, he's gotta be right despite liquids being non-compressible as far as we know. Maybe there's another not-yet discovered thing related to this?
feel really sad that such Informative channels have low subscribers where a random mf doing stupid things on social media have more subs😢
As a man who works on his car, I knew it would go up: like (you have to bleed the) brakes. Plumbers also know this stuff. If you don't know how pressures work, then really bad things happen. This is kind of fluid dynamics in engineering. You can actually feel the different pressures because your blood vessel and heart have to change pressures (like depending on which side you sleep). Anyone who checks blood pressure can witness the difference.
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 am an 8th grade student and I live in Turkey. This experiment has a very easy and practical solution.
Solution: The greater the distance from the top of the water to the bottom, the greater the pressure. If there is water without an air gap higher than the top of the water, this rule applies (translated from Turkish to English)
My explanation:
- the pressure in the air bubble is always the same because its volume is always the same.
- at the interface between water and bubble, the water pressure is equal to the bubble pressure.
- starting from this point up to the pressure gauge, the hydrostatic pressure of the water must be added or subtracted.
- as the bubble rises, this hydrostatic pressure changes because the water column up to the pressure gauge is constantly changing.
- if the pressure gauge is below the bubble, the water column must be added, which is constantly increasing.
- when the pressure gauge is above the bubble, it feels a lower hydrostatic pressure than the pressure at the interface (=bubble pressure).
- as the bubble rises, the pressure difference from bubble to pressure gauge continually decreases and the pressure gauge shows increasing pressure.
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
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.
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
When the air bubble is at the bottom, it has enough pressure to counteract the entire column of water above. This means that when the air bubble moves to the top, it still exerts the same pressure in all directions since it is a closed system, and there is no pressure release.
Therefore, the bubble exerts an overburden pressure from the top now on the entire water column below, which is equivalent to the height of the water column from the "air-bubble-bottom" configuration
Hence, when the air bubble is at the top, pressure at any point in the water column below it will be equal to the (pressure in the air bubble) + (hydrostatic water column pressure).
Of course, there will be some variation due to the elasticity of air, water, and the tubing material.
Two ways i can see someone easily understanding it.
1. Fill a waterbottle with air at the bottom of a pool seal it and then take it to the top of the pool. Open the bottle fast and you can see the pressure that was stored as the weight of the water in the pool was being used to compress the air bubbles.
2. Imagine a large amount of sand over an explosive to absorb the energy, then imagine that same explosive at the top instead of the bottom. Without the sand to compress it its free to show the entirety of energy stored.
Idk feel like it makes sense when viewed like that
The thing that produces the counterintuitive result is the constraint: the system is at constant *volume* and temperature, whereas when we mess around with fluids every day we're more accustomed to situations with a constant pressure applied somewhere. That kind of thing--the behavior changing radically depending on what you hold constant--is a frequent stumbling block in statistical mechanics, which I suppose is really what we're talking about on a microscopic level.
I thought that it’s a hard question, because sealed tubes were always non-trivial and day-to-day logic usually didn’t apply to it; so I didn’t jump to conclusions and thought beforehand. At that moment the answer became obvious (and was indeed the correct one), and the logic was as follows:
1. We won’t think about the part without the bubble at all (because who knows what’s the pressure there)
2. So, we think about the first pressure as the pressure of bubble + small height of water; and the second pressure as the pressure of the new bubble + big height of water
3. The pressure in the bubble remains the same, because it’s volume and temperature both stay the same (thanks to the liquid with constant volume and temperature)
4. And this way, the question is just “What has bigger pressure, small tube of water, or a big one?”
Now it’s obvious, right?
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!
What's interesting though, I wasn't aware water is considered incompressible, my intuition was that the bubble might expand a little, but compress the water some to equalize the pressure again.
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.
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 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.
You could also think the "springiness" of the air bubble bellow as infinite small, so the water wants to flow down but can't because the top side is closed, so the water is getting emerged, that's why it has less pressure. (Just for the intuition part)
If you would open the top side of the tube (when the air bubble is on bottom) the pressure would increase again.
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! ❤❤❤❤❤
Observing Boyle's law, the volume of water must be greater at the top when the air bubble is at the bottom (larger volume = lower pressure). When the bubble rises to the top of the column, the volume of the water decreases thus increasing pressure. I would like to see a measurement of the length of the columns of air versus water in both before and after states to confirm this hypothesis.
3:15 I want to say that the plexiglass setup and the tube setup aren't the same. In the tube setup, there's initially more water above the height of the point at which the pressure is measured. However, in the plexiglass setup, there's exactly as much water below that point's height. Assuming the volume stays the same, this means there's also exactly as much water above that height.
The trick is to find the reference point that has the constant pressure. When the vessel is open, it's the atmospheric pressure at the opening that is constant. When it's sealed however, due to liquid being almost non-compressible, the air bubble is now the constant pressure.
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!
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!
The example with the spring immediately made me understand why it works the opposite way I naively thought it would.
Another way to look at it, when we consider the air pressure to be neutral with the bubble on top: if the air bubble is down, it wants to be "compressed" by the weight of the water above it, so the water is "pulled apart", creating negative pressure similar to capillary forces in trees.
For the sealed idea gas PV=Constant (T is always room temp) and the volume change negligible (neglect the total volume change and liquid volume change), the gas pressure (Pg) remains the same after moving.
Then let H be the height of the liquid column of the side that with the bubble. The pressure at the bottom point is ρgH1+Pg (before) and ρgH2+Pg (after) (Note that H1 and H2 are calculated from different sides as the bubble moved to another side). In this example H1 is smaller than H2, so my answer is the pressure increases.
EDIT:
Note it will be in opposite if the tall side is open (connected to atomasphere). In that case the pressure of the tall side is always ρgH+Patm (H is the height of the column at the tall side), and H goes down after the bubble moving. So the pressure will decrease.
It's a quite normal physics exam problem when I'm in high school back in my country. Difficulty rating is probably 6-7 if represented as a multiple choice. Still glad to see that theory matches the experiment.
I think the easiest explanation is this: pressure is energy density. The total energy of the system is the pressure times volume plus the potential energy of the fluids' positional configuration. By allowing the fluids to reconfigure the net potential energy of the fluids decreases. That lost energy has to go somewhere.
I understood it, when you explained it with the transformation of potential energy into pressure @8:20 . A very interesting problem. Thank you.
Wow !!! I so didn’t expect nor indeed predict the effect once you’d stated the question. Awesome !!!
Imagine it this way:
If you’re in a small room and stand on a spring with your head just barely not touching the ceiling, the spring is compressed by your weight. It pushes back on you, but you don’t really feel the effect.
VS
Stand on the ground and place the spring between your head and the ceiling. The spring is now pushing against the ceiling and down on your head and you likely feel some compression in your neck and spine.
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.
That is such an awesome demonstration, and while it goes against initial intuition, it makes sense mechanically.
basically the air bubbles acts like a compressed gas, hence will exert pressure when at the top of the column
to put it more simple: when the bubble is below, gravity pushes it down, against pressure up. when bubble is high, gravity pushes it down, helping to pressure down. so pressure increases
If you would have measured the pressure inside the air bubble, you would have noticed that it does not change (ideal gas, constant temperature and constant volume). Only the pressure in the water column increases (at any position along the water column). The potential energy of the water mass in the gravitational field is transferred to heat via friction with the tube wall.
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.
Never thought of this problem before until I saw this video. Great topic.
I guessed it would go up because the air bubble is being compressed at the bottom but the water doesn't compress as well in comparison, so in my mind that same amount of pressure isn't being "cushioned" as much and therefore would press it harder. I originally thought that the top was open, in which case I also choose that as the higher pressure one because the same visual amount of space would contain more air if it's compressed by the water.
Yet another way to think of it: when the water is on top, its weight is "protecting" or "shielding" the vessel from having to react to the air spring (i.e., the weight counteracts the force of the spring before it can reach the top of the vessel). When the water is on bottom, the water column just acts as a pass-thru rigid body, hence the vessel is "unprotected" and must stretch to react to the air spring's force.
Increase because incompressible water pushes down and air gap at top can decrease in pressure.
Also it isn't a fully sealed system because the plastic tube has some elasticity especially.
This is legit one of the coolest mathematical physics phenomena I have seen you talk about yet. Bravo!
I think it's wrong.
@@deucedeuce1572 explain.
This isn't "mathematical physics"
@@channeldoesnotexist I mean, ok, it's just physics...
@@channeldoesnotexist It is physics and it could be described with mathematics. I'm sure there are mathematical models for explaining and predicting the pressures at these levels.
I work with hydraulic for work and the best way I’ve heard pressure explained to me is that ‘Pressure is the ability to overcome resistance’ and since water cannon be compressed like a gas the lower in the tube you get the more pressure there is. I got this question correct, thank you for this video I was gripped from the thumbnail
The key point here really is to understand what makes a system isolated. While the tube is sealed it is not gravitationally isolated and thereby there is the potential for a potential difference to occur inputing energy into the system and presenting as an increase in pressure as it is the concentration of energy and thereby the opposite mechanism to entropy