# What is Surface tension: Definition and 205 Discussions

Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows heavier than water i.e., denser than water objects such as razor blades, insects (e.g. water striders), to float and slide on a water surface without becoming even partly submerged.
At liquid–air interfaces, surface tension results from the greater attraction of liquid molecules to each other (due to cohesion) than to the molecules in the air (due to adhesion).There are two primary mechanisms in play. One is an inward force on the surface molecules causing the liquid to contract. Second is a tangential force parallel to the surface of the liquid. This tangential force (per unit length) is generally referred to as the surface tension. The net effect is the liquid behaves as if its surface were covered with a stretched elastic membrane. But this analogy must not be taken too far as the tension in an elastic membrane is dependent on the amount of deformation of the membrane while surface tension is an inherent property of the liquid–air or liquid–vapour interface.Because of the relatively high attraction of water molecules to each other through a web of hydrogen bonds, water has a higher surface tension (72.8 millinewtons (mN) per meter at 20 °C) than most other liquids. Surface tension is an important factor in the phenomenon of capillarity.
Surface tension has the dimension of force per unit length, or of energy per unit area. The two are equivalent, but when referring to energy per unit of area, it is common to use the term surface energy, which is a more general term in the sense that it applies also to solids.
In materials science, surface tension is used for either surface stress or surface energy.

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1. ### Wetting on the outside of a glass cylinder

There are two difficulties, first ##r(y)## is not known, the surface tension force ##F_{surface \; tension}## is not known either. We can write net surface tension force as ##F_{surface \; tension} = \int_0^H 2 \pi r (\sin \arctan \frac{dy}{dr(y)}) dy ## Is there something else we could use to...
2. ### How does soap water membrane thickness affect surface tension?

1.If the thickness of soap water surface decrease, whereas the concentration remain the same, how will the surface tension change? 2. If the membrane of soap water start to evaporate, its thickness become thinner and it’s concentration increase, How will the surface tension change? Thank you!
3. ### Surface Tension: Plate-Water Interface

I would think that a force due to surface tension would act upwards on the plate and not downward, as shown in the diagram I have come up with. The surface of water would act as a stretched membrane and therefore there would be a surface tension on water surface in contact with the bottom of the...
4. ### Why are the three different surface tensions in the directions shown?

I think in the explanation below a very small element of the liquid at the line of contact between the horizontal solid surface, air outside the liquid and the liquid itself is being taken, and forces acting on such a small element are being shown. This very small element is to the left of shown...

6. ### Trying to understand alveolar surface tension

Hello, I learned recently about alveolar surface tension, and the explanation provided in the course was not satisfactory, it said that it is due to the force that pushes water molecules of the outer layer to the inner layers, I don't understand why this force that pushes water toward the cell...
7. ### B Confusion when considering pV=nRT in Two Balloon experiment

This is the Two-Balloon Experiment: https://en.wikipedia.org/wiki/Two-balloon_experiment#cite_note-MW78-1 The claim on Wikipedia which I am a little confused over is that when 2 balloons (at the 2 red points) are connected via a tube, the smaller balloon at a higher pressure would push air...
8. ### I Surface tension and water (the smallest hole water will flow through)

I am trying to find out what the smallest hole water will flow through. not a molecule of water, just water in general. Here is an example. I have a single walled cube that i 3d printed. When i put water in it, it leaks between the layer lines. I want to find out what the spacing between the...
9. ### B Stability of Droplet Climbing on a Needle with Varying Contact Angle

Let's say we are pushing water down a needle, the contact angle between the needle and the water is ##\mathrm{45°}##. For simplicity let's assume there is no gravity. As the water is initially moving down in the left image, the angle ##\theta=\mathrm{45°}## and the surface of the water is a...
10. ### I need an experiment about surface tension

Summary:: Surface tension experiment Does anyone have an idea about a SURFACE TENSION experiment to present as university class work? An experiment that is not too "simple" and repetitive (like things floating under water), and that is well designed.
11. ### I How Does Surface Tension Balance Small Objects on Water Surface?

When small object such as needle is put on the surface of water it displaces small amount of water which creates a depression under the object. Such depression increases surface area of the water because of which surface tension tends to decrease it. Explanation why surface tension balances the...
12. ### I Du Nouy Method for Measurement of Surface Tension

This method calculates surface tension based on force balance acting on the ring placed on the liquid surface: $$F = G + \gamma L$$ where ##G## is weight of the ring, ##L## is wetted length of the ring which is equal to its circumference, ##F## is outer force of tensiometer acting on the ring...

14. ### Problem on Pressure due to Surface tension

The method to solving this is to equate forces along a portion of the balloon through which ##\sigma_L## acts, and another portion through which ##\sigma_t## acts. The former potion should be a circular cross section of the cylinder, while the latter will be a rectangular cross section. You will...
15. ### Good resources for learning basic surface tension

Summary:: Hi, I realized that surface tension is not covered in introductory physics textbooks. Where can I get a good introduction on surface tension? *info provided should be about the same depth as topics in Halliday, Young. Hi, I realized that surface tension is not covered in...
16. ### Calculating the surface tension using the method of Lecomt de Nouy

Hello! I am having unexpected difficulties with this problem.A friend showed me an article regarding the Lecomde ring method,and at the bottom was this little problem that to solve.I've done it like this. $$y = \frac{F}{4\pi r}$$ where F is the given force and r is = 0,0325 in meters. The...
17. ### What is the relationship between surface tension and forces?

Hello! To this I did what was recommended and this is what it looks like $$F = mg$$ $$F = \rho * V * g$$ $$F = \ rho * \pi^2 * h * g$$ Than for the surface tension I did the same thing to get an expression for F. $$y = \frac {F} {2 \pi r}$$ Than tried to get F out and than...
18. ### Water flow rate and drip surface tension

hello i have a drip tube with water dripping and when i increase the flow rate or frequency of drips they get bigger/more massive. i see the equation mass x gravity = 3.14(tube diameter)(surface tension) my mass is changing but not gravity, 3.14 or tube diameter so surface tension must be...
19. ### Surface Tension - Using hot soapy water to wash clothes

I mention the details in the book (verbatim) in the form of a paragraph in green below. Later I ask my questions in blue font for better reading. "Surface tension also explains why hot, soapy water is used for washing. To wash clothing thoroughly, water must be forced through the tiny spaces...
20. ### Experiment involving surface tension for water and alcohol

I really have no idea how to approach this question, I was thinking write ##F=mg## but I am not sure if I can write that even though
21. ### Finding Percent of Water & Oil in a Mixture from Surface Tension

I was looking for on the internet for a while without a success. If I know that the surface tension of pure oil is ##\gamma_o=A## and I know that the surface tension of pure water is ##\gamma_w=B## so if I have a mixture of water and oil with surface tension ##\gamma_m=C## am I able to know...
22. ### I Why volume is conserved but not the surface area?

A water drop of radius ##10^{-2}## m is broken into 1000 equal droplets. Calculate the gain in surface energy. Surface Tension of water is ##0.075 ~N/m##. So, for the solution of the above problem we need to know how much surface area (combining all 1000 droplets) have increased from the...
23. E

### Surface tension and Young's contact angle

I came across this diagram, the ##\gamma##'s are supposedly forces per unit length of the respective interfaces: It's not clear what these forces are acting on. ##\gamma_{SL}## and ##\gamma_{LG}## look like they could be acting on a small bit of water right at the end, but I have no idea what...
24. ### Viscoty and Surface tension -- depends on the composition of the atmosphere?

why isn't Surface tension reliant on the composion of the atm? For an instance; If you place a glass of water in a room with regular atmosphere or you place it in a room filled with other gasses. The coefficient of surface tension of the fluid will change? Maybe? why isn't viscoty of a fluid...
25. ### How does water rise along a glass plate? (surface tension question)

So, I was studying about general properties of matter and topics like surface tension. I came across the phenomenon of water rising along a glass plate like in the picture. I looked for some mathematical interpretation of this on the internet and in some books. [![enter image description...
26. ### Force due to Surface tension here

Why does the force due to surface tension act parallel to the surface here? I know that surface tension is a result of absence of cohesive force above the surface and thus the water molecules below pulls the surface down and keeps it like a stretched membrane. If the surface is pressed as...
27. ### Reason for Calculating Surface tension

When calculating force due to surface tension across a hemispherical drop, we look at only the circumference and multiply it by the value of surface tension. When we know that it is the surface tension which is responsible for the curved surface of the liquid drop, why don't we calculate the...
28. ### Surface Tension and Capillary Rise

According to this definition I am unable to understand why does surface tension acts tangentially to surface of contact of liquid and capillary tube. And is the force of surface tension balancing the adhesive forces which lead to capillary rise OR it is the reason behind the capillary rise?
29. ### Factors affecting surface tension

I read the following two points: Temperature is indirectly proportional to surface tension. Adding impurities affect the surface tension of the molecules. Adding soluble impurities increases the surface tension whereas adding sparingly soluble impurity decreases the surface tension. Why...
30. ### Surface Tension: Why Tangential and Not Downward?

Why direction of surface tension is tangential to the surface and not perpendicular downwards since it is caused by molecules in the bulk?
31. ### Classical Resnick Halliday Walker -- do they discuss surface tension topic?

Is surface tension topic present is resnick halliday walker, principles of physics 10th edition,if present then please tell me on which page
32. ### I Strain of of a bubble's surface interface during vibrations

Imagine a bubble vibrating in air. Because it vibrates, it's interfacial area increases, thus new molecules are added and removed from the surface as it vibrates. Consider a molecule is initially at position X_0 at the interface, and over a certain amount of time molecules squeeze and disappear...
33. ### I Would an unstable emulsion separate in the abscense of gravity? How?

If you have two different liquids (water and oil for example) mixed together and free floating without gravity, will they separate as they do here on Earth? If so, what property would determine the layering structure? I suspect they would separate, and if left undisturbed probably form a...
34. ### Relationship between Excess Pressure and Surface Tension for a Drop on a Fibre

Homework Statement Think of a drop of radius ##R## deposited on a fibre of radius ##b(b<<L)##.Find ##{\Delta{P}}## Homework Equations The relationship between excess pressure and the surface tension is given by Yong-Laplace equation, $$\Delta{P} = \sigma{(\frac{1}{R_1}+\frac{1}{R_2})}$$ The...
35. ### Shape of a bubble inside a rotating container

1. A closed cylindrical vessel filled with water (at room temperature) contains a small air bubble of normal pressure and volume ##V=1~{cm}^3## inside in it.The cylinder is then started to be rotated slowly with a small angular acceleration in a complete weightlessness (at a space station)...
36. ### How the forces on a drop of water versus mercury on a glass slide influence the shape?

I am trying to understand how fluids form particular shapes when put on a solid. In the two figures,what are we taking as a system for the forces? How the resultant of the forces influences the shape of the different fluids?
37. ### Explaination of Solid-Liquid and Solid-gas surface tension

I am a high school student and currently studying Mechanical properties of fluid. We are taught surface tension in a very introductory level and most of it is about liquid-gas surface tension. We are taught that liquid-vapour tension is the atrractive forces that water molecules experience at...
38. ### Surface tension in terms of temperature and concentration of an added substance

Hi! Here's a tricky thermodynamics problem, I hope you can help with it. 1. Homework Statement The boundary between two different materials can be divided into two different kind of phases: bulk phases and surface phases. For example, let's consider a boundary between water and air. We can...
39. ### Calculating surface tension with the Capillary Equation

Homework Statement Hello everyone, I am doing an experiment and I've hit a snag with my calculations. I am looking at how concentrations of soap affect surface tension in water. I am have been using the capillary equation and capillary tubes for my calculations. I have practiced this method for...
40. ### What do surface tension vectors mean in this quote?

I was reading Fundamentals of Inket Printing and it said the following: "The surface tension in a liquid causes a force to act in the plane of the free surface perpendicularly to a free edge in that surface." Can someone explain to me what this means? What's the direction of the force? I have...
41. ### What is the thickness of the drop if its radius is r?

1. A small drop of fat floats on the surface of a liquid whose surface tension is s. Surface fat tension at the air-fat interface is s1, at the fat-liquid interface is s2. Determine the thickness of the drop if its radius is r.2. ##F=\sigma l## ##\delta P=\sigma (\frac 1 R_1 + \frac 1...
42. ### Surface tension trivial problem

1. The films of the two liquids are separated by a bar of length l. The coefficients of surface tension of liquids are equal to s1 and s2, respectively. What force acts on the bar on the liquid side?(It is a rectangular surface of 2 liquids separated by a bar of length l) 2. Force=(surface...
43. ### How Does the Cassie-Baxter Model Explain the Lotus Effect?

1.The lotus effect refers to self-cleaning properties that are a result of ultrahydrophobicity as exhibited by the leaves of "lotus flower". Dirt particles are picked up by water droplets due to the micro- and nanoscopic architecture on the surface, which minimizes the droplet's adhesion to that...
44. ### The shape of the surface of a soap film

1. Two coaxial rings of radius R=10 cm are placed to a distance L from each other.There is a soap film connecting the two rings(that looks like a cylinder which have different radii with z coordinate. (The rings lie in xy plane)).Derive a differential equation describing the shape r(z) of the...
45. ### Does an ideal fluid have zero surface tension?

Does ideal fluid have zero surface tension? What does zero surface tension signify?
46. ### Calculation of the weight of an insect floating by surface tension

Homework Statement The surface of a liquid is just able to support the weight of a six-legged insect. The leg ends can be assumed to be spheres each of radius 3.2 × 10−5 m and the weight of the insect is distributed equally over the six legs. The coefficient of surface tension in this case is...
47. ### Surface Tension of needle on water

I attempted the question but it was wrong... I don't understand where i went wrong my working seems logical, can someone please help. When a needle is gently placed on the surface of still water (γ = 0.0730 N.m-1) it can be supported by surface tension if the mass of the needle is small enough...
48. ### Surface Tension, find number of stitches to be made

Homework Statement The tension in the skin of the left ventricle of heart is 4.90 N/m. A cut is made on the left ventricle during surgery. How many stitches must be used to repair the cut? Each stitch will safely support a tension of 0.4 N. Homework Equations Surface tension = force/length...
49. ### Area of common surface of two bubbles

What will be the area of common surface of two identical bubbles of radius R , i know there common surface will be flat as the radius of curvature of comman surface will tends to Infinity , but how do i relate with area of flat surface I tried to use Energy = Surface tension * area And then...
50. ### Molar volume and surface tension of nanoparticle

Hi .how can i calculate the molar volume and surface tension of nanoparticles ? shoud i have to calculate? or these parameters is available in tables or sth?