Finding height of fluid in a barometer | Fluids | Physics | Khan Academy

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Using our understanding of fluid pressure to figure out the height of a column of mercury. Created by Sal Khan.
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[@piacorujo4161]

this dude is the reason i'm going to do well on the mcat

[@prabhanshukatiyar213]

you having cold, sal?

[@erictoepfer4655]

1 atm = 101325 Pa

[@alig5904]

1 atm = 101.3 kpa ?

[@Fin2001]

Ali G 101325 Pa

[@aksh_x_]

It's hard to believe that I'm getting all this for free! Thanks a lot Sal, and I will sure donate once I start earning.

[@VSmassacre]

"Let me draw a bowl...a bowl.. And in this bowl i have Mercury" -LOL

[@IdoAloni123]

N is not M*m^2/sec^2, it is J You just wrote N/m^3 instead N/m^2 (pressure) The mistake is in the last equation

[@calebcar]

This series is wonderful. I'm taking an on line ap physics course and there is no audiovisual. You are a life saver. One thing I don't understand. I did not see that you made reference to the diameter of the test tube. If the test tube took up almost the entire diameter of the bowl the mercury was in, wouldn't you have a tiny surface area of air pushing a large surface of mercury up. Why does the height not depend on the relative surface area of air and mercury?

[@coolradio123]

did you ever find out why? 🙂

[@markharlock6474]

It is counter-intuitive, but the pressure exerted at the base of a column of liquid is independent of the diameter of the column (in this case a long vertical test tube containing mercury). This can be shown in the derivation of the formula P=pgh used in this video. With the density of mercury (p) and 'g' both constants, the pressure (P) at the base of the column of fluid is seen to be directly proportional only to the height (h) of the column of fluid. So the diameter of the tube does not affect the equilibrium level of the fluid column. However, you would have to be sensible about choosing larger diameter tube since this would require a larger volume of mercury in the 'bowl'.

[@michellephil413]

lmao i love the word vaccuum bc theres 2 u's in a row

[@8299naresh]

I have started loving Physics.......(nd I'm doing my computer science)

[@GreerFried]

8:16 it should be m^2.

[@jonrty007]

Isn't 1 atm = 101.325 kPa or 101,325 Pa? :O Other than that. You are probably one of, if not, the greatest Physics teachers alive.

[@seekdragonflies]

he is talking about mercury when he refers to 13.6 g/cm^3 or 13,600 kg/m^3 which is the density of mercury :)

[@uriyacohen-eliya7932]

Amateur mistake on the units there sal.... N is kg*m/s^2, not kg*m^2/s^2, you wouldn't be left with m as it would cancel.... Your mistake was with canceling 1/m^2 in the numerator with 1/m^3 on the denominator......

[@biochem86]

1 atm=101325 pascals or 101.325kpa

[@mrd7765]

It would be great if it was Mahesh sir...I can't understand Sal sir but I can understand anything easily when it was Mahesh sir..

[@nestoloco]

I noticed the same thing, 1atm=101325 Pa

[@Joikakaker]

Why are you defining 1 atm as being at sealevel in Paris, France? It's not constant there, nor is it constant anywhere else. I guess you already know this, and I guess you just say it to simplify things, but it's quite important to know that pressure is dynamic (hence our dynamic weather)

[@adas2922]

thanks

[@asganesantpr]

whether there would be some changes in mercury level(760 to anything) if i change the area of the bowl ??

[@Peter_1986]

"Aluminium" is more consistent with other metallic elements, like sodium, magnesium calcium etc, and from a Latin perspective more correct.

[@Vayrus53]

yes it is 101325 pascal. 1 atm = 1.01325x10^5 Pa

[@TurbotortoiseStickle]

Thank you, I'm actually having fun with this.

[@joel7308]

u r great, thank u, other parts r also good

[@joltzvoltz6314]

isn't 1atm= 101300 pa

[@Verschlimmbesserung]

And 101300 pa is = 101.3 kpa, since 1kpa is 101300.

[@Verschlimmbesserung]

Sorry, 1kpa= 1000pa.

[@Joikakaker]

@jiggaluv123 I wouldn't say that saying that pressure is dynamic is very complicated, rather quite intuitive

[@asherzephyr]

So does the mercury go into the tube because the atmospheric pressure basically pushes it into the tube?

[@nguyenphuonganh340]

At the last minute, 103000 N/m^2 should be the numerator instead of 103000 N/m^3. And 1N = (1 kg * 1m)/(s^2).

[@thienfoil]

@g37muflih force has to do with mass and accel/gravity. Pressure is force over an area. Force doesnt need to stay constant, but pressure in liquid does.

[@lastword5714]

can u please provide lecture on gear design?

[@fleshcookie]

lets say we have that bowl Sal!

[@travel_n_fun]

Ehm, in the formula (bottom right hand corner, you wrote 103,000N/m^3, when it should be m^2 :)... Thanks a lot Sal!!!!

[@anilsharma-ev2my]

Half filled barometer doings some work or not ?

[@arjunaumesh5375]

Kg m/s^2 is N And pressure is N/m^2 Small error

[@2007excalibur2007]

@g37muflih The same reason why we can't call pressure as force.

[@littlelulu123456]

could i just borrow your brain for the mcat nov 7? LOL

[@syedfazalhussain6471]

What did you score on the MCAT?

[@michaelproctor2529]

For those who care, this is why your Beerita doesn't spill all over the restaurant table.

[@xdodanielodx3835]

This vid triggered my imagination. Smh. It was useful, though. As always. Keep it up!

[@mariyamlee1125]

test tube looked more like a villi!lol!

[@guitarded0081]

does that mean that no matter how big the test tube the mercury will always goe up 0.77 m at 1 atm ???

[@2007excalibur2007]

@jonrty007 If he needed to round it off he could've at least just used 10^5 Pa, lawl.

[@bubshab]

Think you got your atm to pascal conversion wrong buddy. Cheers for the vid anyways.

[@d3fil4dddsspecz]

1 atmosphere is 101k pascal not 103k

[@khushi-gn1zz]

still didnt get it

[@dinmorerengeit]

is it just me or does the units not work out..? isnt N= m*a = kg*m/s^2? N =/= kg*m^2/s wich means he will not end up with .77m in his answer..

[@AzizSobirov]

2:45 Vacuum it has 2 u so it must be W lol

[@7starblast414]

wait,if an elephant smacks u, u get hurt due to the pressure or its momentum?

[@kkngenomesho7744]

come on...

[@chrisbotos]

You hurt because your nerves feel the change in the pressure and inform the brain with pain signals. But you also hurt because the momentum resulted in a force on your nerves that broke parts of them, in this case your nerves also send signals of pain. So the answer is both.

[@7starblast414]

@@chrisbotos well thanks for reminding me i commented something that stupid over two years ago. Thanks for answering anyway haha

[@lucasmontec]

It's still mercury:?

[@izzyAKAisra]

in my physics class my professor drew the same thing and everyone thought he was drawing a DiICK! Guess what the professor said! : " I dont know where you get that from but that's not physics(Russian accent )

[@MattOGormanSmith]

In our school, we'd lose a mark for not drawing the negative meniscus on the mercury.

[@nikunjtiwari2739]

google says 1atm = 101325 pascals

[@KP-wc6hm]

1atm=101325pa

[@chrisbotos]

I don't think you need to know how atm relate to Pa you can just google it and I don't think any exam will require for you to know it

[@abhishek56555]

noo

[@nehaabbasi3741]

Be my physics teacher pls😏

[@C0rtny]

Did anyone else jump at 2:50 ?

[@AmirMullick]

No guitarded0081.

[@TeKNiQ50]

i effing WUB u

[@MusicMenacer]

the drawings are helpful, but a bit of a waste of time to watch you draw. the mercury for example

[@coltwhat]

i thought 1 atm = 101300 Pa? =S

[@noname2useable]

he is american, thats the american pronunciation

[@GoodbyeRubyTu3sday]

there is no sea in Paris

[@Physicsiseverything]

Isnt mercury red??.....

[@travel_n_fun]

Ehm, in the formula (bottom right hand corner, you wrote 103,000N/m^3, when it should be m^2 :)... Thanks a lot Sal!!!!