Physics 33.1 Surface Tension (9 of 12): Pressure in a Soap Bubble

[@rosbifattack430]

Hi, why u take A = pi*r² and not 4*pi*r² at 3:10 ?

[@MichelvanBiezen]

Because you need to only count the force components in the vertical direction.

[@pasindupalihawadana]

Even after 10 years of publication, your Video helped me.. Thank You Sir! im from Sri Lanka.

[@MichelvanBiezen]

Welcome to the channel. (Physics doesn't age). 🙂

[@magendungu8499]

I am wondering why we do not consider the atmospheric or hydro pressure acting on the bubble from outside. thank you

[@MichelvanBiezen]

the inside atmospheric pressure cancels out with the outside atmospheric pressure

[@tsui886]

Sir, do pressure in bubble mean the difference of pressure inside and outside of bubble? I feel confused as i found out many source also stated this

[@tsui886]

Which mean the resultant pressure adding a force that is opposite to the surface tension?

[@MichelvanBiezen]

That is correct. The surface tension causes the pressure inside the bubble to be greater than the pressure outside the bubble.

[@DatBeast18]

@@MichelvanBiezen Does this also apply to the double soap bubble? Or is that different as the bubbles aren't technically complete?

[@akashsunil7464]

proffesor michel van biezen since there are two layers of the bubble it can effectively be blocked by the two layers and hence the effective area where it acts can be only pi(R^2-r^2) i know its a stupid question but its just a doubt

[@CossZt6]

Can the proportionality factor 2pi*r basically be derived by integrating along the path along which the surface tension acts for an arbitrary surface? (Of course in this case for a sphere)

[@aleah1381]

I didn't quite understand why L was 2 times the circumference of the cross sectional of the bubble. Is the cross sectional the middle of the 2 surfaces?

[@MichelvanBiezen]

There is an inside surface and an outside surface to a bubble. Thus you have to multiply the circumference by 2.

[@DearlyDepartedDaz]

Assuming you went to lectures to learn what you're lecturing on. Do most lectures use an example or do they explain the equation and it's uses then give an example?

[@MichelvanBiezen]

Adam White I am not sure which lectures you are referring to and what you want to know, Are you referring to the lectures on this channel? If yes, then I can say that the lectures are a combination of explaining the theory and then showing examples, at least that is the case for most of these videos.

[@DearlyDepartedDaz]

Michel van Biezen It is probably just me. I've been diagnosed with extremely irregular thinking patterns. Thanks for providing these in any case. Helping to understand a new theory I'm working on.

[@calebhan1767]

How you can just consider cross section area of half sphere, while surface tension should place entire cross section?

[@MichelvanBiezen]

I don't quite understand your question. Are you asking why I only consider the area of the cross section and not the area of the entire semi spherical surface? If so, then the answer is that we only need to consider the perpendicular components of the force vectors against the surface.

[@jferro96]

to find the total pressure do you multiply by 2, since you only found the pressure on half of the bubble? or is it for both?

[@MichelvanBiezen]

+J Ferro Pressure = force / area, so you divide the force by the total area.

[@rajasribala8750]

Hi, This is Rajasri, Your Teaching/ Explanation is fantastic in all the videos but one thing I would like suggest you, please improve the video clarity what your writing or drawing on board.

[@MichelvanBiezen]

Yes, our old videos did not have the clarity, which we corrected with our newer videos

[@homratha4820]

thank you so much and can you have exercises book? please

[@MichelvanBiezen]

We haven't made those yet. Those may come in the future.

[@chinnadurai4110]

Why excess pressure acts on one side of hemi-sphere not on other side sir?

[@Vandevodius]

I tried to make a Bubble in my hand by a Soap.I Made it but it is combined with water which is combined with soap.if I blow The bubble,The bubble pops out bevause of the water.Why so? Thank you.

[@MichelvanBiezen]

Different soaps have different ingredients which affect their ability to make bubbles.

[@lananhtran1124]

Sir I don't really understand the term "effective area" and how we use it to calculate pressure. Why is the area of the cross-section is the "effective area" but not the dome shape? Can you explain, please? Thank you very much.

[@MichelvanBiezen]

Note that the forces near the "equator" of the bubble push mostly sideways and only the vertical component of those forces push down on the bubble. So when we only add the vertical components to obtain the total force, it would be the same if the bubble was "flat".

[@rkusuma6852]

hi sir, I don't really get your comment where you said that "the vertical component of those forces push down on the bubble" to my understanding it looks like the forces are acting upward, how can they be pushing down on the bubble?

[@karenjoycadiz3322]

what about if the radius is not given, only the surface tension

[@tsoojbaterdene7793]

Hat off to you such a hardworking teacher.Why haven´t you gotten a Nobel prize.I am serious!!

[@MichelvanBiezen]

Each of us has been given a gift from God and a purpose in life. Those who find that purpose and use their gift to better the world have all the reward anyone can ask for.

[@mightyaxis3123]

When we add more air to the air bubble why the pressure inside decrease, from ai to google everyone say same thing but can't prove it. Kindly someone help

[@annapurnadey7082]

what happens when air is blown in a soap bubble? Thank you

[@MichelvanBiezen]

Pressure inside increases and the bubble will expand.

[@tsoojbaterdene7793]

How to find the atmospheric pressure outside the soap bubble,Sir?

[@MichelvanBiezen]

We can probably assume that atmospheric pressure outside the soap bubble = 1 ATM = 101325 Pa (N/m^2)

[@AshotH6]

If surface tension of the soap water is lower than water, how come we can't make water bubbles?

[@MichelvanBiezen]

Ashot, The answer in nature always comes from understanding the forces that affect the situation. When you have water in small quantities, the molecular forces of attraction between the water molecules combined with the surface tension (which is also a result of the molecular forces of attraction between the water molecules will pull the water into a spherical water droplet. A soap bubble is something completely different. A mixture of water and soap can be pulled into a sheet as long as the water to soap ration is correct. The sheet can then be bent by blowing air into it. If the curvature is great enough, the bent sheet can from into a bubble with air inside so that the wall of the bubble is like a bent sheet. The forces between the water molecules will not allow for such an air bubble to exist within the water bubble

[@AshotH6]

Michel van Biezen thank you for the explanation. Also thank you for all the videos that you have made. They are very helpful. I have set a goal to study every physics and chemistry playlist that you have posted.

[@geethachandrasekar3245]

Sir make a video in sums

[@suhaib1183]

Thanks so much sir for clearing my doubt regarding the effective area we are considering in case of bubble.

[@MichelvanBiezen]

You are most welcome

[@philwesom8784]

really good :) i love your channel

[@doordie7560]

your lectures helped me alot...& some small details In every topic u provide helps to grasp concepts easily...thanxx alot..

[@ByteMock]

Very helpful with my my hw thank you!

[@MrDuocheng]

I love you Sir!

[@dipraj]

thanks

[@MichelvanBiezen]

Welcome

[@shubhamajumder3630]

Thnx

[@tteedghihh]

dyne? What a stupid unit to use. Use Newtons!

[@Vandevodius]

How Stupid u are.Hypocrite.Newtons Were used for Energy and Dyne is different from Newton.Use ur brain.