<< Chapter < Page Chapter >> Page >

Surface tension is proportional to the strength of the cohesive force, which varies with the type of liquid. Surface tension γ size 12{γ} {} is defined to be the force F per unit length L size 12{L} {} exerted by a stretched liquid membrane:

γ = F L . size 12{γ= { {F} over {L} } } {}

[link] lists values of γ size 12{γ} {} for some liquids. For the insect of [link] (a), its weight w size 12{W} {} is supported by the upward components of the surface tension force: w = γL sin θ size 12{W=γL"sin"θ} {} , where L size 12{L} {} is the circumference of the insect’s foot in contact with the water. [link] shows one way to measure surface tension. The liquid film exerts a force on the movable wire in an attempt to reduce its surface area. The magnitude of this force depends on the surface tension of the liquid and can be measured accurately.

Surface tension is the reason why liquids form bubbles and droplets. The inward surface tension force causes bubbles to be approximately spherical and raises the pressure of the gas trapped inside relative to atmospheric pressure outside. It can be shown that the gauge pressure P size 12{P} {} inside a spherical bubble is given by

P = r , size 12{P= { {4γ} over {r} } } {}

where r size 12{r} {} is the radius of the bubble. Thus the pressure inside a bubble is greatest when the bubble is the smallest. Another bit of evidence for this is illustrated in [link] . When air is allowed to flow between two balloons of unequal size, the smaller balloon tends to collapse, filling the larger balloon.

Sliding wire device which is used to measure surface tension shows the force exerted on the two surfaces of the liquid. This force remains a constant until the film’s breaking point.
Sliding wire device used for measuring surface tension; the device exerts a force to reduce the film’s surface area. The force needed to hold the wire in place is F = γL = γ ( 2 l ) size 12{F=γL=γ \( 2l \) } {} , since there are two liquid surfaces attached to the wire. This force remains nearly constant as the film is stretched, until the film approaches its breaking point.
When two balloons are attached to the ends of a glass tube air flows from one to the other if their sizes are different.
With the valve closed, two balloons of different sizes are attached to each end of a tube. Upon opening the valve, the smaller balloon decreases in size with the air moving to fill the larger balloon. The pressure in a spherical balloon is inversely proportional to its radius, so that the smaller balloon has a greater internal pressure than the larger balloon, resulting in this flow.
Surface tension of some liquids At 20ºC unless otherwise stated.
Liquid Surface tension γ(N/m)
Water at 0 º C size 12{0°C} {} 0.0756
Water at 20 º C size 12{"20"°C} {} 0.0728
Water at 100 º C size 12{"100"°C} {} 0.0589
Soapy water (typical) 0.0370
Ethyl alcohol 0.0223
Glycerin 0.0631
Mercury 0.465
Olive oil 0.032
Tissue fluids (typical) 0.050
Blood, whole at 37 º C size 12{"37"°C} {} 0.058
Blood plasma at 37 º C size 12{"37"°C} {} 0.073
Gold at 1070 º C size 12{"1070"°C} {} 1.000
Oxygen at 193 º C size 12{ - "193"°C} {} 0.0157
Helium at 269 º C size 12{ - "269"°C} {} 0.00012

Surface tension: pressure inside a bubble

Calculate the gauge pressure inside a soap bubble 2 . 00 × 10 4 m size 12{2 "." "00" times "10" rSup { size 8{ - 4} } `m} {} in radius using the surface tension for soapy water in [link] . Convert this pressure to mm Hg.

Strategy

The radius is given and the surface tension can be found in [link] , and so P size 12{P} {} can be found directly from the equation P = r size 12{P= { {4γ} over {r} } } {} .

Solution

Substituting r and γ size 12{g} {} into the equation P = r size 12{P= { {4γ} over {r} } } {} , we obtain

P = r = 4 ( 0.037 N/m ) 2 . 00 × 10 4 m = 740 N/m 2 = 740 Pa . size 12{P= { {4γ} over {r} } = { {4 \( 0 "." "037"`"N/m" \) } over {2 "." "00" times "10" rSup { size 8{ - 4} } `m} } ="740"`"N/m" rSup { size 8{2} } ="740"`"Pa"} {}

We use a conversion factor to get this into units of mm Hg:

P = 740 N/m 2 1.00 mm Hg 133 N/m 2 = 5.56 mm Hg . size 12{P= left ("740"" N/m" rSup { size 8{2} } right ) { {1 "." "00"`"mm"`"Hg"} over {"133"`"N/m" rSup { size 8{2} } } } =5 "." "56"`"mm"`"Hg"} {}

Discussion

Note that if a hole were to be made in the bubble, the air would be forced out, the bubble would decrease in radius, and the pressure inside would increase to atmospheric pressure (760 mm Hg).

Got questions? Get instant answers now!

Questions & Answers

Two bodies P and Quarter each of mass 1000g. Moved in the same direction with speed of 10m/s and 20m/s respectively. Calculate the impulse of P and Q obeying newton's 3rd law of motion
Shimolla Reply
definition for wave?
Doc Reply
A disturbance that travel from one medium to another and without causing permanent change to its displacement
Fagbenro
In physics, a wave is a disturbance that transfers energy through matter or space, with little or no associated mass transport (Mass transfer). ... There are two main types ofwaves: mechanical and electromagnetic. Mechanicalwaves propagate through a physical matter, whose substance is being deformed
Devansh
K
Manyo
thanks jare
Doc
Thanks
AMADI
Note: LINEAR MOMENTUM Linear momentum is defined as the product of a system’s mass multiplied by its velocity: size 12{p=mv} {}
AMADI
what is physic
zalmia Reply
please gave me answar
zalmia
Study of matter and energy
Fagbenro
physics is the science of matter and energy and their interactions
Acquah
physics is the technology behind air and matter
Doc
Okay
William
hi sir
Bala
how easy to understanding physics sir
Bala
Easy to learn
William
31. Calculate the initial (from rest) acceleration of a proton in a 5.00×106 N/C electric field (such as created by a research Van de Graaff). Explicitly show how you follow the steps in the Problem-Solving Strategy for electrostatics.
Catina Reply
A tennis ball is projected at an angle and attains a range of 78. if the velocity is 30metres per second, calculate the angle
Shimolla
what friction
Wisdom Reply
question on friction
Wisdom
the rubbing of one object or surface against another.
author
momentum is the product of mass and it's velocity.
Algayawi
what are bioelements?
Edina
Friction is a force that exist between two objects in contact. e.g. friction between road and car tires.
Eklu
With regards to a shielded cable, is there an induced current on the shield when the center conductor is carrying an AC Current? What is the formula?
John Reply
what is phenomena
remilekun Reply
no idea
Awoke
its phenomenon, an observable fact.
author
Mujy achy marks hasil krny k leay kesy tayari krni ho ge?plz help me I'M sooo woried
Imran Reply
konsi university m ho and konsa course h
Mohit
what is force
Chukwuemeka Reply
Force is the cause and momentum is its effect.
Salman
A force is a pull or a push on an object, causing an object to move or a moving object to stop.
Eklu
Find the velocity that make one full oscillation in 10 seconds and also makes 1.7meters in the same time
Prince Reply
yes
Rafael
OK
Oluwaseun
17m/s
Eklu
17m/s
Gabriel
0.17
Devansh
17m/s
Harrison
how did you solve it
Acquah
t=10s a=1.7m v=? u=0 but v=u+at but u=0 v=at 1.7×10=17 v=17m/s that's how I solved it.
Eklu
kk
Acquah
How is a=1.7m?
El
a is an acceleration
El
eklu..... I respect u....
Doc
its relating to time and oscillation made.
Eklu
You mean A as an amplitude?
El
ok
Emmanuel
what is voltmeter
Jeremiah Reply
A voltmeter is a device use in measuring electric potential in a volt.
Ahmad
Find out the equation of a simple harmonic progressive wave that have 0.2m with a frequency of 550hertz.If the wave moves along a positive x axis with the speed of 330m/s
Joseph Reply
is there a summary for this whole physics book
Fortune Reply
I don't think there is a summary for this physics
Adeyemi
nope
Idy
I want a guide book on Ray optics
Sharma
Where to get?
Sharma
ok
Jude
hi
Tina
pleasant evening
Idy
evening dr
Betman
what the difference between laws and principles
Mary Reply
principle are like rules... it can change BUT LAW IS LAW... confirmed theory
Fortune
principle is a guiding belief Law is authority or instruction
Faruk
Hello want to study physics but it seems so difficult
Joshua Reply
Yes
Aifuwa
I read it but when I try to solve questions it seems difficult
Aifuwa
Jerry where are you from
Joshua
can i study some problem on motion and projection motion
Weamie
hello pls am new here so i want someone to highlight me on this "application of expansion/contraction
Awoke
want 2 do is just dat u rest for some minute,then u go back to the simple one nd one u understand and then go back to d difficult one,u will now understand it better.
rebecca
yess
rebecca
what of mine
Awoke
yess
rebecca
ok
Awoke
iam new here
Mohamed
u are welcome
Awoke
hello am new. am I welcome
Miracle
yes you are😁
clifford
we can all learn and help each other
Osei
yeah you are right
Neyaz
so we can all share our ideas on a certain topic
Osei
sure
clifford
in beginning all subjects are difficult need to work hard
Mohammed
hi guyz
Lamin
How can I understand physics
Thankgod
Where will I start from
Thankgod
(fundamentals of physics) start there
clifford
OK thanks
Thankgod
Hello, im college now, engineering, 1 years, what book of physics i must use, to be understand easily?
Megryan
try physics for scientist and engineers/ cutnell and Johnson
clifford
Okey po!
Megryan
Is not difficult if u really want to learn
Gabriel
hello guys
Okotie
i love physics but it is difficult for me to solve
Okotie
I just saw d group on my physics app
Charles
xame here
Kpogho
pls guys i need help on my physics understanding and i know that if we share ideas together we can make this world a better place using more advance level of technology cos we are the new generation and we need to make technology more advance and introduced to under develop countries.
Sammy
i think we need to b focus when learning or studying physics,making research on topics or words that seems difficult , putting them into practice or analyzing the idea to our day to day activities and introducing it to other.
Sammy
i just think that is a way we can improve and highlighting our selves on physics so that those who want to learn will learn and those who want to know will know that there is still some generation scientists who can improve technology today.
Sammy
i don't think if what i sed make sense but i still think it those
Sammy
physics is a course that goes like this, if you don't put in the work it doesn't matter how much help you get, you will never truly understand
clifford
what is this group for please?
Charles
if u ask people or internet for understanding u will get d idea of how physics play it's game on every topic
Sammy
hellow guys am persuing science laboratory technology which physics book should I use so that I understand the concepts of physics well
Nasike
yh me too
Ozuruonye
essential physics or new school physics is good but u can also download MCQs physics handbooks
Sammy
just for beginners
Sammy
is true
Ali
hello guys
Okotie
please who can teach me physics
Okotie
Ok
Zazy
i can
Sammy
hi
divine
pls am new here and I really want someone to teach me physics
divine
Practice Key Terms 5

Get the best College physics course in your pocket!





Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'College physics' conversation and receive update notifications?

Ask