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How does sap get to the tops of tall trees? (Recall that a column of water can only rise to a height of 10 m when there is a vacuum at the top—see [link] .) The question has not been completely resolved, but it appears that it is pulled up like a chain held together by cohesive forces. As each molecule of sap enters a leaf and evaporates (a process called transpiration), the entire chain is pulled up a notch. So a negative pressure created by water evaporation must be present to pull the sap up through the xylem vessels. In most situations, fluids can push but can exert only negligible pull , because the cohesive forces seem to be too small to hold the molecules tightly together. But in this case, the cohesive force of water molecules provides a very strong pull. [link] shows one device for studying negative pressure. Some experiments have demonstrated that negative pressures sufficient to pull sap to the tops of the tallest trees can be achieved.

When the piston is raised the liquid stretches somewhat, which results in negative pressure.
(a) When the piston is raised, it stretches the liquid slightly, putting it under tension and creating a negative absolute pressure P = F / A size 12{P= - F/A} {} . (b) The liquid eventually separates, giving an experimental limit to negative pressure in this liquid.

Section summary

  • Attractive forces between molecules of the same type are called cohesive forces.
  • Attractive forces between molecules of different types are called adhesive forces.
  • Cohesive forces between molecules cause the surface of a liquid to contract to the smallest possible surface area. This general effect is called surface tension.
  • Capillary action is the tendency of a fluid to be raised or suppressed in a narrow tube, or capillary tube which is due to the relative strength of cohesive and adhesive forces.

Conceptual questions

The density of oil is less than that of water, yet a loaded oil tanker sits lower in the water than an empty one. Why?

Is surface tension due to cohesive or adhesive forces, or both?

Is capillary action due to cohesive or adhesive forces, or both?

Birds such as ducks, geese, and swans have greater densities than water, yet they are able to sit on its surface. Explain this ability, noting that water does not wet their feathers and that they cannot sit on soapy water.

Water beads up on an oily sunbather, but not on her neighbor, whose skin is not oiled. Explain in terms of cohesive and adhesive forces.

Could capillary action be used to move fluids in a “weightless” environment, such as in an orbiting space probe?

What effect does capillary action have on the reading of a manometer with uniform diameter? Explain your answer.

Pressure between the inside chest wall and the outside of the lungs normally remains negative. Explain how pressure inside the lungs can become positive (to cause exhalation) without muscle action.


What is the pressure inside an alveolus having a radius of 2 . 50 × 10 4 m size 12{2 "." "50" times "10" rSup { size 8{ - 4} } `m} {} if the surface tension of the fluid-lined wall is the same as for soapy water? You may assume the pressure is the same as that created by a spherical bubble.

592 N/m 2 size 12{"592"`"N/m" rSup { size 8{2} } } {}

(a) The pressure inside an alveolus with a 2 . 00 × 10 4 size 12{2 "." "00" times "10" rSup { size 8{ - 4} } } {} -m radius is 1 . 40 × 10 3 Pa size 12{1 "." "40" times "10" rSup { size 8{3} } `"Pa"} {} , due to its fluid-lined walls. Assuming the alveolus acts like a spherical bubble, what is the surface tension of the fluid? (b) Identify the likely fluid. (You may need to extrapolate between values in [link] .)

What is the gauge pressure in millimeters of mercury inside a soap bubble 0.100 m in diameter?

2 . 23 × 10 2 mm Hg size 12{2 "." "23" times "10" rSup { size 8{ - 2} } `"mm"`"Hg"} {}

Calculate the force on the slide wire in [link] if it is 3.50 cm long and the fluid is ethyl alcohol.

[link] (a) shows the effect of tube radius on the height to which capillary action can raise a fluid. (a) Calculate the height h size 12{h} {} for water in a glass tube with a radius of 0.900 cm—a rather large tube like the one on the left. (b) What is the radius of the glass tube on the right if it raises water to 4.00 cm?

(a) 1 . 65 × 10 3 m size 12{1 "." "65" times "10" rSup { size 8{ - 3} } `m} {}

(b) 3 . 71 × 10 –4 m size 12{3 "." "71" times "10" rSup { size 8{4} } `m} {}

We stated in [link] that a xylem tube is of radius 2 . 50 × 10 5 m . Verify that such a tube raises sap less than a meter by finding h for it, making the same assumptions that sap’s density is 1050 kg/m 3 size 12{"1050"`"kg/m" rSup { size 8{3} } } {} , its contact angle is zero, and its surface tension is the same as that of water at 20.0º C .

What fluid is in the device shown in [link] if the force is 3 . 16 × 10 3 N size 12{3 "." "16" times "10" rSup { size 8{ - 3} } `N} {} and the length of the wire is 2.50 cm? Calculate the surface tension γ size 12{g} {} and find a likely match from [link] .

6 . 32 × 10 2 N/m size 12{6 "." "32" times "10" rSup { size 8{ - 2} } `"N/m"} {}

Based on the values in table, the fluid is probably glycerin.

If the gauge pressure inside a rubber balloon with a 10.0-cm radius is 1.50 cm of water, what is the effective surface tension of the balloon?

Calculate the gauge pressures inside 2.00-cm-radius bubbles of water, alcohol, and soapy water. Which liquid forms the most stable bubbles, neglecting any effects of evaporation?

P w = 14 . 6 N/m 2 , P a = 4.46 N/m 2 , P sw = 7.40 N/m 2 . alignl { stack { size 12{P rSub { size 8{w} } ="14" "." 6`"N/m" rSup { size 8{2} } , } {} #p rSub { size 8{a} } =4 "." "46"`"N/m" rSup { size 8{2} } , {} #P rSub { size 8{"sw"} } =7 "." "40"`"N/m" rSup { size 8{2} } "." {} } } {}

Alcohol forms the most stable bubble, since the absolute pressure inside is closest to atmospheric pressure.

Suppose water is raised by capillary action to a height of 5.00 cm in a glass tube. (a) To what height will it be raised in a paraffin tube of the same radius? (b) In a silver tube of the same radius?

Calculate the contact angle θ size 12{θ} {} for olive oil if capillary action raises it to a height of 7.07 cm in a glass tube with a radius of 0.100 mm. Is this value consistent with that for most organic liquids?

5.1º size 12{5 "." 1°} {}

This is near the value of θ = size 12{θ=0°} {} for most organic liquids.

When two soap bubbles touch, the larger is inflated by the smaller until they form a single bubble. (a) What is the gauge pressure inside a soap bubble with a 1.50-cm radius? (b) Inside a 4.00-cm-radius soap bubble? (c) Inside the single bubble they form if no air is lost when they touch?

Calculate the ratio of the heights to which water and mercury are raised by capillary action in the same glass tube.

2 . 78 size 12{ - 2 "." "78"} {}

The ratio is negative because water is raised whereas mercury is lowered.

What is the ratio of heights to which ethyl alcohol and water are raised by capillary action in the same glass tube?

Questions & Answers

Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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How we can toraidal magnetic field
Aditya Reply
How we can create polaidal magnetic field
Mykayuh Reply
Because I'm writing a report and I would like to be really precise for the references
Gre Reply
where did you find the research and the first image (ECG and Blood pressure synchronized)? Thank you!!
Gre Reply
Practice Key Terms 5

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Source:  OpenStax, Physics 101. OpenStax CNX. Jan 07, 2013 Download for free at http://legacy.cnx.org/content/col11479/1.1
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