8.01x - Lect 27 - Fluid Mechanics, Hydrostatics, Pascal's Principle, Atmosph. Pressure
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- Опубликовано: 7 фев 2015
- Fluid Mechanics - Pascal's Principle - Hydrostatics - Atmospheric Pressure - Lungs and Tires - Nice Demos
Assignments Lecture 25, 26, 27 and 28: freepdfhosting.com/03ca75eadf.pdf
Solutions Lecture 25, 26, 27 and 28: freepdfhosting.com/f15cd35103.pdf 
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I am preparing for IITJEE and I started detesting physics , love for chemistry and maths increased but by watching your lectures sir , a new love for physics emerged in me . Thanks a lot.
Me also preparing for JEE, what's your rank in advance
@@virajgoyanka5150 me kvpy
Me too😁
Hey Did you crack IIT JEE Exam ???
@@virajgoyanka5150 same goes for me now
Hallo Prof. Lewin, believe it or not, lately as i come back home from the office, i watch your video while having my dinner. It feels like i was watching a TV serie. I am a postdoc now but everytime i see your taped class i feel like i was a fresh student in a senior high school. i really love the way you teach..
GREAT! :)
such love :)
@@lecturesbywalterlewin.they9259 sir take my Pronam ang great love
35:15 reminds me of a trip to Hawaii. Went to the top of the volcano in Maui (about 10000 ft) and drank a plastic bottle of water. I put the cap back on and drove back to sea level. The bottle was completely collapsed by the atmospheric pressure. Most impressive demo to my wife.
As an Engineering Student, I have always loved your Lectures, Professor Lewin. They've helped me a lot throughout my courses.
About the last experiment at 48:10: Mr. Lewin is draining all the air which is in the hose at the beginning by sucking in an amount of air that is subsequently released through the nose while blocking the end of the tube with the tongue. Doing so he creates a "vacuum" and the atmospheric pressure does the rest, basically it pushes the juice all the way up until it reaches a state of equilibrium. Assuming the juice has the same density as water, Mr. Lewin could suck the juice up to ~ 10 meters, maybe 11 meters if the human body has the capacity to generate a pressure equivalent to 1/10th of 1 atm. If we do this with a high density liquid the result would be way different.
Thank you Mr. Lewin for sharing your passion with all of us and all the love and effort you put into these lectures. Greetings from Canary Islands. :)
But if that also works on the manometer experiment, does that mean that you could snorkel much deeper underwater?
These lectures are truly a treasure, not only are the lectures themselves being offered at no charge but also a set of homework problems along with their solutions. Thanks a lot!!!!!
I love how the camera randomly zooms in on students taking notes
It feels like I am in the class and looking around for a second to relax my brain.
@@user-do1dc3qf3c it gets distracting looking at others i feel
Hello, Prof. Lewin. I am from India and have been following your lectures in 11th and 12th. Currently, I am in medical school and even now your lectures help reinforce the concepts and clear any doubts that may arise as one studies a topic. Thank you so much for uploading your lectures and helping hundreds and thousands of students around the world. Great fan of your lectures and your works and researches in Physics.
The Professor"s lectures are more comprehensible than the Adverts that accompany them.
they have a freaking rifle in class.... this is the most awesome lecture ever !
:)
Air rifle, dare I say
Robert Petrey
He put in a bullet.
@@rebirth_mishap LOl thats a real rifle, looks like a 22. Its bolt action.
In 1999 teacher shows rifle in physics class....nobody bats an eye.
15 to 20 years later.....people claim the teacher is endangering students...gets fired.
When he uncovered that rifle I could barely believe it. Great professor.
This man is the reason im interested in physics, that silky smooth voice MMMMMMMMMMM i could listen to his lectures for hours
This man is crazy ❤️
Wish I could get a teacher someone like him.
You're the reason of many students who has started to love Physics again, Professor Lewin.
prof. Lewin.......I read your book..for the love of physics and that also brought me to here..you are indeed as good as they say...it was super fun attending this lectures..in india...my local school teachers never teach with such methadology which makes physics interesting as much as u are making
But brother why you say about our indian teachers?
Thanks professor for existing in this world!
So that was actually the atmospheric pressure itself which was responsible for the high level of Cranberry juice. Suckling the air out of the pipe did that trick. You are a awesome teacher. Your lectures will inspire students for 100 of generations for sure.
:)
Every lecture of Professional Walter Lewin piques my interest and love for Physics. Thank you Professor Lewin.
I'm immensely grateful to have these courses available for free here, and become a better engineer, and hence, a better man. Thank you professor, I will contribute to return the favor. 🙏the only thing I would suggest to add, is an explaination of what pressure is at the molecular level. I found it very helpful to understand why fluids behave in these strange ways, and to connect the concept of pressure (collisions) to temperature (agitation).
Helps greatly to understand concepts of basic physics. Thank you professor.
For the last question :
When you SUCK air you are effectively trying to create a vacuum inside your lungs, so the model which is being recreated here is a barometer with water in it . And equating the pressure developed due to the juice to the atmospheric pressure we will get a certain limiting height (10meters for water) the hose is shorter than that so you are able to drink the juice.
If I suck several times, locking the hose end with the tongue, while re-filling my lungs, I imagine, I I'll drink manometer fluid. Atmospheric pressure will allow me doing this. In one continuous sucking it seems to be impossible as we've seen in the class. It's only my imaginary. Please let me know if I'm wrong. When I have free time, I'll prepare such fluid based manometer to check my imaginary.
In my previous comment, I should write emptying my lungs instead of re-filling.
i used to wonder why everyone watched and admired walter lewin , now i get it a mad science lover who also loves too teach and does dare to any experiment
I will never forget this lec prolly and i wished i had studied under u
All that I will say is that I completely agree with the name of this channel. Watching these videos really makes you love physics. I have loved it since many years now. Nonetheless, it is a delight to watch these videos.
Thank you for your passion for sharing your knowledge and making us understand how the universe works, Mister Lewin! It is great to have you! I wish you and your family a very happy and healthy new 2024 year!
You are a great treasure to the World! 🙏
Wow you are amazing professor!!! Before watching this I always wondered how pascals law is consistent with the law of conservation of energy...Thanks a lot...
professor this Sunday i have competitive exam and your lecture is very useful so thank you!
Excellent! Good luck on your exam.
Hua clear ?
@@lecturesbywalterlewin.they9259 Hi lecture can you make a web fluid n web shooter real life
I was doing similar experiments at home some time ago and i was just as surprised as you about how many percents of a vacuum i could get. It's actually enough to create a strong enough vacuum for certain experiments.
I found another way of measuring the vacuum or overpressure by the way and it takes a lot less room. Fill a hose with water and trap some air at the end of the hose then close that end. If you suck on it and the air bubble doubles in size then obviously you've managed to lower the pressure to half an atmosphere. So it's easily possible to draw a scale on the hose, that indicates the pressure.
Great lecture by the way!
:)
There was only like button but i loved the leacture !!! 😊
:)
Hey ,as a 14 year old, and physics enthusiast I am truly addicted of your lectures.
:)
I have a lot of cleaning up to do, but do realize people sometimes rewatch your lectures while cleaning! We just need to listen to it all again (which is better than TV)
sir your lectures are awesome, it is a real love of physics
Professor, regarding the question at the end of the lecture: the earlier demo had shown your lung to be capable of 0.1atm overpressure for both inhalation and exhalation. In the final demo, you use this inhalation several times to get the juice up to you. The height it rises over each inhalation depends on lung capacity. You exhale through your nose while keeping the end of the hose in your mouth. Probably, you have closed that end using your tongue. (Those creates a barometer like situation)
One more observation: if it were water, for hose length > 10m, the water would slip down to the 10m level each time you are not inhaling.
This means that the maximum length of the hose for water can be 11m for an overpressure of 0.1atm
correct
I really enjoy your lectures. Such a great teacher
:)
I’m here because of my homework. And I really like the explanation! I enjoyed the video and you earned a new subscriber :D. The name of the channel is correct: this makes me love physics (but I also liked it before ;D)
you are breathing out all the air inside the hose with the help of your nose (letting air out) so that you can suck more air afterwards from the hose itself ,up till the cranberry juice comes to your mouth (removing all the air),and also their will be some height at which you can no longer suck the juice up because of the atmospheric pressure.
:)
Lectures by Walter Lewin. They will make you ♥ Physics. also very warm wishes for your 81st birthday professor >>>keep inspiring us
why is there "some height at which you can no longer suck the juice up because of the atmospheric pressure"? is it related to the barometer?
Dear sir, do you have a chapterwise playlist or i have to search individually for each lecture?
I was learning about it 7 lessons and didn’t understand anything. After 2 minutes of watching it taught me more than during my science class. Thank you!
You are right emma
🎯 Key Takeaways for quick navigation:
00:34 🌊 Pressure is defined as force divided by area, measured in pascals (N/m²). Pascal's principle states that pressure applied to an enclosed fluid is transmitted undiminished throughout the fluid and to the container walls.
02:00 🌬️ In a static fluid, the force exerted by the fluid on any surface must be perpendicular to that surface, as any tangential component would set the fluid in motion.
04:04 🚗 Pascal's principle allows for the creation of hydraulic jacks, where a small force applied over a larger area can lift a much larger weight.
05:28 🛠️ Hydraulic jacks do not violate the conservation of energy; work done to compress the fluid on one side is recovered as gravitational potential energy when lifting the weight.
07:20 🌍 Gravity affects fluid pressure; as you go deeper into a fluid or down into the ocean, pressure increases due to the weight of the fluid above.
11:49 ☁️ Atmospheric pressure, also known as barometric pressure, is due to the weight of the air above and is generally considered one atmosphere, roughly equivalent to 1.03 x 10⁵ pascals.
16:30 💡 Torricelli's barometer experiment demonstrated that the height of a liquid column in a tube is directly proportional to the atmospheric pressure, with mercury creating a column of about 76 cm.
26:09 🍷 Historical experiments were done with various liquids, including red wine for barometric measurements, and showed that liquids with different densities require different column heights to maintain atmospheric pressure.
30:57 ⚖️ Cornelis Van Drebbel built one of the first submarines in the early 17th century, around 1622, which could operate at a depth of about five meters with half an atmosphere of hydrostatic pressure.
35:10 🌊 Atmospheric pressure exerts significant forces, as demonstrated by the collapsing paint can when the air inside was evacuated.
36:43 🏊 When snorkeling or scuba diving, it's essential to counteract the hydrostatic pressure with pressurized air, as the forces can be immense. Snorkeling depth is limited by the ability to generate an overpressure in the lungs.
46:03 🍹 Contrary to lung limitations, a long tube can be used to siphon liquids from considerable depths due to different principles, like atmospheric pressure and gravity.
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sir i got to know about u by physics wallah and tommorow is my physics test and ur class helped me a lot , huge huge thanku and love from india ❤❤😊😊
Idk why but I can still understand his lectures at 1.5 times the speed.. awesome lectures
Sir I am from India and your lecture is really awesome
you made me fall in love with physics, thank you teacher
I tried the snorkeling thing when I was a kid, I went to the beach and I tired to improve my hold breath time, so I dove with a plastic bottle and the idea was: when I reach my time limit i grasp air from the plastic bottle. I couldn't pull a single gram of air; even when squeezing the bottle I had barely enough air to reach my lung.
almost drowned myself, but I learned a valuable physics lesson that day.
Very clearly explained... You are the best physics teacher... Initially I didn't have any interest in physics, but your lectures addicted me to physics... May I know what inspired you to become a physics teacher?
very great explaination ive just feel the physics right now
Hi Prof. Lewin, hope you're keeping safe in Hawaii! Regarding the hydraulic jack, is it right for me to say that using Pascal's idea we are effectively able to "split" the work needed to lift a car up by say 10cm into multiple repetitions of muscular motion, so that mere humans can do so? That is to say, without such a machine is maybe quite impossible to lift the car with a single motion of human arms (since the power required is not feasible), but the jack breaks it down into managable loads (albeit at lower power i.e. much more "time" required than a single lift)?
I wish I had lectures like these, my current fluid mechanics teacher is using paint for online classes
this is the best lecture ever
In the sucking experiment in the first case the pressure was generated with the lungs, in the second one with the mouth. Mouth can generate greater pressure or vacuum than lungs because it's smaller in volume and its muscles are comparably strong.
Way better than any movie, way better
had a very heavy headache, but that doesn't stop me to watch till the end. Much love Prof!
16:34, did he roll the chalk to make those dashed lines?! How to make dashed lines so quickly is worthy of a lecture itself... Until then, thank you so much for sharing these on youtube!
ruclips.net/video/raurl4s0pjU/видео.html
Ahh, lead with the contact point and turn the chalk into a 'paw'l. Nice. Thank you!
About the last qs: Probably you were squeezing the end of the tube by your fingers repeatedly for maintaining pressure difference made by each inhale and also to have a time for the next inhale. Thus creating enough vacuum for atm pressure to raise juice (maximum at 10 meters). Correct me if it is not the case.
It’s about time you all figured it out.
Sir I think in the first case as u said just do in a one blow,the air in the chest after one blow would run out but in the second case u may have lifted the liquid just by sucking it many times as u are free to do.
Sir in the last experiment does the barometric pressure help you in drinking the juice since it pushes the juice up and then you suck the rest in?
Great lecture! I wonder whether in the first manometer experiment the limiting factor is not so much the pressure the lungs can generate, but rather the total amount of air they can expire (5-6 litres). With a rigid pipe, the same amount of air might generate a much higher pressure than 0.1 atmosphere? Easy to check by repeating the experiment with a pump, limiting the amount of added air to 5 litres (which would give the same result, not explained by pressure limitations of the pump) or by using a rigid pipe (which would give a large pressure if the volume explanation is correct) for comparison? For snorkeling, deeper depths would still be a problem, as breathing in and out of a large tube is expected to lead to low oxygen and increased carbon dioxide levels over time as exchange of gas with the air outside the tube would be too limited. Whether inhaling in at 2 meters below the surface of a pool is feasible is fairly easy to check with a rigid pipe?
The atmospheric pressure on the surface area of the juice that you drink up is (I'm guessing) about 10x that of whats pushing on the fluid in the manometer simply because its in a wider vessel and has more surface. Its basically just the hydraulic jack in reverse.
What wonderful man like you! All my life I hate physics due to teachers. It's unfortunate that I lost that opportunity in senior school to be watching videos like this. I love your teaching method professor. I learned better through visually seeing things how they happen in real life. Any video related to biophysics in the series? Thank you sure much:)
:)
3:28 this observation is also applicable to Brazil's colloquial language
This was awesome man! Love your teaching always! But, experiments to the level of using guns in class? OH YESSS!!!😊👍👍👍
These are the best lectures ever. thank you so much. What happens if I dive under water 2m f.e. with a bucket of air and try to breathe in there. would that work or does the same rule apply for the snorkeling?
Sir you always make us love physics
The best lecture ever
You don't know how happy I am. Thank you
You're welcome 😊
love u sir and your great lecture..
:)
Hello Pr.lewin
I want to know that in equilibrium for some water in a glass, which forces cancels each other to put that volume of water in an equilibrium case I mean that
for example if we put the solid obj on the table or any surface in the statical equilibrium kind, the normal force of that surface and weight force of an obj , cancels each other
and I want to know what happen for the liquid like water in the glass of water on the table ,
of course I searched internet and google and I found that pressure- gardiant force cancels mg of liquid in the hydrostatical case ,
but
what about normal force of cross section of that glass???
???
and are there any forces except them ????
please guide me more ??
thanks a lot !!! .
Great and bizarre lecture! And I think the answer to the question of why the height is higher than one meter which is what was obtained in the previous experiment is the following (what I think and I'm not sure):
Assuming the pressure generated by the professor's lungs is the same in both cases, the reason the height is higher is; because in the first case (manometer) the atmospheric pressure is against the pressure exerted by the professor's lungs, while in the second case it's assisting the professor in sucking in the juice since the pressure exerted by the professor is the same but in this case, is negative hence dP would be:
1 atm - (-P) = dP = 1 + P atm
where P is the professor's "suction pressure".
you are amazing,professer..the last part made me giggle alot..thank you
Hello professor, hope that you are in a great state of health and jovial as always.In your book "For the love of Physics" , at the end of the chapter "The Magic of Drinking with a Straw" you pose a question that whether we can snorkel much farther down beneath the surface of a lake or sea using the same trick that you employed in sucking the cranberry juice up to 16 feet.
Well, I think the answer is NO.Because in the classroom when you are sucking the juice, every time after sucking when you can't take any more air in you exhale and start sucking again.But you can do that easily because the pressure on your chest is only 1 atmosphere.When you are beneath a water body, in order to inhale you need to expand your chest to a sum total of atmospheric and hydrostatic pressure which will increase with depth and thus you cannot repeat inhalation many times.Please let me know if I am thinking along the correct path.
Thank you.
Sir,
How we can increase the thrust from water output of convergent divergent nozzle by mixing air thorough water.
regarding experiment with air suction
case 1: U-shaped tube: you did a single breath and since your lungs/chest can't expand more the liquid moved by one meter and stopped
case 2: straight tube: the pressure in a tube is reduced not using your lungs but with mouth muscles. Thus you were able to reduce pressure gradually and release the air trough your nose (while closing with a tongue.
2. correct
Does the difference in surface area play a role in being able to suck the cranberry juice from the beaker as well, as in a hydraulic lift? If the surface area exposed to the atmosphere were the same as the cross-sectional area of the tube, it must be much harder to suck the juice up because you would not have the assistance of atmospheric pressure times the exposed surface area of the beaker.
I think that the answer to the last question is; as he sucks up the liquid he is actually expending his chess so the low pressure in the chess equilibrates with the 1 atm in the tube by raising the liquid, and he seals the tube with his tongue to breathe out and sucks again and so on. You can suck up to 10 meters (water), at 10 meters the hydrostatic pressure equilibrates with the atmospheric pressure so if you try to suck from that point you need to generate under pressure (in Mr. Walters case it is a 1 m extra, assuming the water won't start boiling). Please correct if I'm wrong. Greetings from Turkey.
Sir you are awesome. I wish I have a professor like you in my school.
:)
Thank you for your reply sir ... I'm from India and I really wants to join MIt. Your teaching methods are really exciting sir...
For the final demonstration it does not matter how many draws you take, approximately 1m head of water is all the chest cavity can deliver.
What is actually happening is Professor Lewin is using the smaller volume of the mouth cavity and strength
of his tongue to generate the reduced pressure and to seal the tube between draws while simultaneously isolating the lungs from the tube pressure. This is the normal method of sucking everyone instinctively knows as an infant. To draw up a liquid using lung pressure risks inhalation of the liquid into the lungs, a potentially dangerous method.
Pascal's Principle is exactly applicable in 0 gravity ( in the iss )
Sir if i decrease the radius of the connecting u shaped tube in hydraulic jack...will there be any changes?
Hello Prof. Lwein, thank you for the amazing lecture, but i got a bit confused here, because according to Pascal's Law, pressure is the same at an enclosed fluid, then why P=ρgh which indicates the pressure is not the same at different high. Why is this, is the word "enclosed" the keypoint here?
Same confusion here
As shown in the lecture, in case of gravity there is a pressure difference at vertical direction.
the liquid when enclosed has no effect on it by the air. if u take a completely enclosed fluid up then it wont have any affect on it. the difference comes due to the liquid being exposed
Had you proceeded in steps for the first try(snorkeling), that level difference could have gone higher than 1m as well(right ?). While driving all that air out in one go instead, you were pretty much also reaching the sustainable strain limits of the lungs.
🙏 God Bless Harmony Sithole for introducing me to this man.
Another great course. One thing I don't quite understand on the snorkeling. When I was 12 my father and I went snorkeling and dove up to 10 meters deep to the ground of the sea where a boye was. With no pressurized air how can our body sustain that amount of pressure?
I understand that the gas in the blood is neglectable (as long as you didnt intake pressureized air) and the only problem are the lungs, but I am still amazed.
My only guess is, that the few liters of air are beeing compressed and the rips are flexible enough?
These lectures are great treat for all physics lovers
While you did the last experiment,was it possible because u did not suck up the liquid in one go, but let it raise-block the atm pressure--exhale--release and suck more--repeat? Whilst it wasn't done with the manometer or atleast not attempted
proffeser, is it that you can easily suck up the cranberry juice, because due to the pressure the juice ends up going upward, and since it's under the 10m limit you can easily drink the juice? am I correct?
best lecture professor i never seen teacher like you............................if this lecture would be convert in Hindi ideo then most of the students would get benefit of this .............
+NIKHIL SHUKLA My lectures are being viewed about 6 million times a year. 20% of these are people from India where many can read English. The subtitles help a lot I hope!
thanks for replying me professor.........yes subtitle helped us a lot............but now i am able to understand you without subtitle because i became a habitual of listening your word..
+NIKHIL SHUKLA Super so you no longer need subtitles. !!
yes professor............i am not believing that i am talking wit you............in my life i want to meet with you .....and i believe that definitely i will be meet with you....... .
+NIKHIL SHUKLA Nikhil, I am running this site and I am \\/\/////@lter Lewin. It would be great to meet. Don't wait too long as I am almost 80. Where do you live?
I got the answer anyway. thanks for the cool videos
sir it helped me to clear my concepts for jee. Thank you so much.
Walter , i think I know the explanation, is it because in the last experiment you blew many times and in the time between the blows you didn't let any air in, so you kept the pressure, and then you blow again, and lower the pressure even more and this goes on and on, is that it?
Hallo Sir, where can I find the answer to the question you posed at the end of the lecture ?
He is basically sucking the juice up, then breathing in and sucking again. Since he closes the tube at the top, atmospheric pressure at the bottom does not allow the juice to fall back into the glass again
Wow...... That was awesome 👌
In the case of the hydraulic jack, gravity neglected, as F1 is not equal to F2, there is an external force on the system (fluid). So it must have acceleration. But it doesn't, is this because there is a normal force by the container on the fluid?
At the end, I believe in the previous example, you can only go about 1 meter because you are pulling nearly the entire weight (mg) of the liquid by your sucking force. At the end, you have the weight (mg) of the liquid in the container, not yet in the tube, assisting you. It would probably not get difficult until the E(Fy) in the tube and in the container are slightly unbalanced in the negative. I.E. Mtube*g >= Mcontainer*g.
you didn't get it (yet)
Can we also understand liquid pressure in molecular scales?
Because I can’t do many questions without analyzing it exactly I have to analyze it correctly
Thanks a lot sir... Now I have gotten what atmospheric pressure is?
Excellent
Does it have to do with the forces of surface tension, that helps you fight gravity a little thus you can suck with relative ease than the manometer ?
+Ahmed Rohaim NO
@Alexandru Guja for some reason i can't reply to your comment. When he put his finger and stopped the juice from falling I think it was a hint, he probably did the same with his tongue. xD
Tasos Obscure Tasos, yes that is correct I close the tube with my tongue.
Is it because of capillary action that you could suck the cranberry juice from way high?
If I had a box full of water and none could escape and I took it down under the ocean really deep, would the pressure be different inside of the box or will it stay the same as being above the sea?
the pressure of the ocean acts on the external box.. but the pressure inside the box remains same..
Lovely lectures❤
Ah so this is where RUclips has taking me at 1:30am
:)
I am reading this comment at 1:40 AM
It's 2:04 am for me.
Damn it is 2 am, and I cannot sleep
@6:00 when we are adding an extra pressure more than 10 kg..the right sides moves up..will they then be in equllibrium afterwards or else what will happen ?
These systems have a HUGE amount of friction and they are operated with pneumatic power. If you buit a small one in the lab with near zero friction in the "platforms" The platforms will not be at equal level. Make a free body diagram! The levels of the platforms will come to a rest when in a horizontal plane, going through both sides, the hydrostatic pressure is the same. If you then place some weight on one side again the levels will move till the hydrostatic pressure is the same in any horizontal plane.