# surface tension Definition and Topics - 37 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. ### 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...
2. ### 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...
3. ### Good resources for learning basic surface tension

Summary:: Hi, I realised 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 realised that surface tension is not covered in...
4. ### 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...
5. ### 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...
6. ### 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...
7. ### 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...
8. ### 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...
9. ### 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...
10. ### Drop deposited 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...
11. ### 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)...
12. ### 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?
13. ### 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...
14. ### 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...
15. ### Surface tension problem

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...
16. ### 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...
17. ### Does an ideal fluid have zero surface tension?

Does ideal fluid have zero surface tension? What does zero surface tension signify?
18. ### 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...
19. ### 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...
20. ### 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...
21. ### How surface tension is measured for molten metals?

Hello How the surface tension is measured for molten metals? I have heard about the sessile drop, but it seems to be a very inaccurate method... Thank you for your time. Regards.
22. P

### When does gravity take over surface tension?

I want to demonstrate to flat earthers that water does indeed stick to a ball. If we want to do a scale model of the earth, at which radius will gravity overcome the surface tension?
23. ### A Question on surface tension

Homework Statement [/B] Water rises in a capillary tube to certain height such that the upward surface due to surface tension is balanced by 7.5 X 10-4N Force due to weight of the liquid. If the surface tension of water is 6 X 10-2Nm-1,the inner circumference of the capillary must be Homework...
24. ### Minimum radius of bubbles in a soda bottle (surface tension)

Homework Statement [/B] The question is from chapter 9 of "Exercises in Introductory Physics" by Leighton and Vogt. The answer given in the book is ##R = 4.9 \times 10^{-5} \rm{cm}##. Homework Equations $$\sigma = \frac{\Delta P \cdot R}{4}$$ Where, ##\sigma## is the surface tension...
25. ### I Measuring advancing contact angle

Hi everyone ! I'm currently working on a project for which I need to measure the advancing contact angle of a liquid on a solid, specifically the advancing contact angle of a molten thermoplastic on carbon fibers. My understanding is that there is a difference between dynamic contact angles...
26. ### I The difference between capillary number and Laplace number?

It seems that both the capillary number and the Laplace number represents the relative effect of viscous forces and surface tension. Can anybody explain the difference between them? Thanks a lot. I have attach the Wikipedia- links to these two concepts...
27. ### Height of Meniscus

I've been reading up on capillary action in a tube, and I have some questions: Say we insert a tube in a pool of fluid; Jurin's Law expression is ##h=\frac{2\sigma \cos \phi}{r\rho g}##. However, this height is not the height of the fluid measured from the bottom of the tube, but rather the...
28. ### Upside down Cup with water to hold the plate

During high school; I thought atmospheric pressure is so strong that plate will remain intact to the glass full of water when made upside down. But when we decrease the density of the fluid to the air; this phenomenon wont' work. That means atmospheric pressure is not only playing role in this...
29. ### Help on surface tension

Having trouble to understand a classical example of surface tension: Two balloons are connected to each other with a valve. If the surface tension of the two balloons is the same but one balloon is bigger than the other, when the valve is lifted open so the air in the two balloons is now...
30. ### Surface tension of water

a thin film of water has surface tension due to the strong bonds present on the surface in order to counteract the net downward force and this increases the potential energy of the surface layer of particles therefore on a hydrophobic surface it forms a water droplet , my question is since it...