Surface Tension - What is it, how does it form, what properties does it impart

How does surface tension affect the surface properties of a liquid? Looking at surface tension from a particle perspective and a macro perspective, this video shows what causes surface tension, how surface tension is manifested in our everyday lives, and how intermolecular forces are involved in surface tension.
-More on Surface tension | Wikipedia- 1/5/2018:
Surface tension is the elastic tendency of a fluid surface which makes it acquire the least surface area possible. Surface tension allows insects (e.g. water striders), usually denser than water, to float and stride on a water surface.
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). The net effect is an inward force at its surface that causes the liquid to behave as if its surface were covered with a stretched elastic membrane. Thus, the surface becomes under tension from the imbalanced forces, which is probably where the term "surface tension" came from.[1] Because of the relatively high attraction of water molecules for each other through a web of hydrogen bonds, water has a higher surface tension (72.8 millinewtons per meter at 20 °C) compared to that of 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 free energy.
Water[edit]
Several effects of surface tension can be seen with ordinary water:
Beading of rain water on a waxy surface, such as a leaf. Water adheres weakly to wax and strongly to itself, so water clusters into drops. Surface tension gives them their near-spherical shape, because a sphere has the smallest possible surface area to volume ratio.
Formation of drops occurs when a mass of liquid is stretched. The animation (below) shows water adhering to the faucet gaining mass until it is stretched to a point where the surface tension can no longer keep the drop linked to the faucet. It then separates and surface tension forms the drop into a sphere. If a stream of water was running from the faucet, the stream would break up into drops during its fall. Gravity stretches the stream, then surface tension pinches it into spheres.[3]
Flotation of objects denser than water occurs when the object is nonwettable and its weight is small enough to be borne by the forces arising from surface tension.[2] For example, water striders use surface tension to walk on the surface of a pond in the following way. The nonwettability of the water strider's leg means there is no attraction between molecules of the leg and molecules of the water, so when the leg pushes down on the water, the surface tension of the water only tries to recover its flatness from its deformation due to the leg. This behavior of the water pushes the water strider upward so it can stand on the surface of the water as long as its mass is small enough that the water can support it. The surface of the water behaves like an elastic film: the insect's feet cause indentations in the water's surface, increasing its surface area[4] and tendency of minimization of surface curvature (so area) of the water pushes the insect's feet upward.
Separation of oil and water (in this case, water and liquid wax) is caused by a tension in the surface between dissimilar liquids. This type of surface tension is called "interface tension", but its chemistry is the same.
Tears of wine is the formation of drops and rivulets on the side of a glass containing an alcoholic beverage. Its cause is a complex interaction between the differing surface tensions of water and ethanol; it is induced by a combination of surface tension modification of water by ethanol together with ethanol evaporating faster than water.
Check out other popular CC Academy videos on this channel:
Stoichiometry Tutorial, step by step
Classifying Types of Chemical Reactions
Solution Stoichiometry
Orbitals, the Basics: Atomic Orbitals Tutorial
Hybrid Orbitals Explained
Polar Molecules Tutorial: How to determine polarity in a molecule
Metallic Bonding and Metallic Properties Explained
Covalent Bonding Tutorial
Ionic Bonds, Ionic Compounds: What is an ionic bond and how do ionic compounds form
Electronegativity and bond character (bond type): non-polar covalent, polar, ionic
Metric Unit Prefix Conversions
Metric unit conversions shortcut
Mole Conversions Tutorial
Frequency, Wavelength, and the Speed of Light
The Bohr Model of the Atom and Atomic Emission Spectra
What is Heat
Rutherford's Gold Foil Experiment
Unit Conversion Using Dimensional Analysis Tutorial
What is Fire: Combustion Reaction Tutorial

[@seanewing204]

Fast, concise, thorough, and easily understood. Brilliant!

[@williambrewer]

Probably best video on surface tension I've seen.

[@zafarahmedghouri61]

I would never have understood this concept, if it wasn't for your video. 👍

[@mahsansiddiqui904]

It is amazing, it is really really amazing, before watching this video i am unable to understand that what is surface tension but after watching this video, this topic became one of the most easiest topic for me

[@CrashChemistryAcademy]

Great! Thanks for watching!

[@matematicasybarcos]

Great explanation. Thanks a lot for sharing this content!

[@thanishbolla3989]

Separating molecules requires work to be done against the attractive forces. So because molecules in the surface don't have molecules above them, they need less energy to move down into the bulk of the liquid than is needed for molecules to move from bulk to surface. Therefore the rate of movement of molecules due to their random thermal energy is greater surface to bulk than bulk to surface. [Compare Boltzmann factors exp(−ES to BkT) and exp (−EB to SkT).] This tends to deplete the surface layer, which in turn reduces the movement of molecules from surface to bulk, re-establishing (dynamic) equilibrium (equal rates of movement to and from the surface layer). But with this 'new' dynamic equilibrium, the molecules are further apart in the surface layer than their usual separations so, recalling the intermolecular force curve, they attract each other, in other words the surface is under tension, like a stretched balloon-skin

[@shaktigg]

yes . and what is said in vid at 1:24 is wrong

[@Venu_G_Dash]

I don't get that if the rate of movement of molecules from surface to bulk is greater, than how does that REDUCE the movement of molecules from surface to bulk.. What I mean is, how does the "tendency towards depletion of surface layer" REDUCES the movement of molecules towards bulk ? Its been a whole year since you posted your comment but I'll be happy to get a response. Thnx 😄

[@krumkutsarov618]

Thanks. Was confused why the video says the concentration at the top is higher.

[@Justsomeguy560]

So during online classes my teacher sent the whole class the link of this video .lol

[@CrashChemistryAcademy]

I can live with that.

[@sandeedakhter3409]

Same

[@WaqasAhmad-fx5wh]

@@CrashChemistryAcademy Sir in our chem book the definition of surface tension is The surface tension is the amount of energy required to stretch or increase the surface of a liquid by a unit area Sir I think this definition is wrong cox we says that the surface molecules are compressed and they are experiencing inward pull so the surface area should be decreased not increase .Sir what do u think it should be increased or decrease.

[@bensurinal556]

@@WaqasAhmad-fx5wh yes

[@krishnatalari1871]

@@WaqasAhmad-fx5wh In the definition what they mean is "the amount of energy(per unit area) which you should apply externally so that it exactly balance the surface energy per unit area(or surface tension)"

[@islenomaleconalfombra8997]

Omg, it's the only video where I could undertand it. Thank you!

[@wgjohnson]

Very well explained and nice visuals.

[@aarepresent]

Excellent video. Efficiently explained .

[@NiharikaAChirayil]

Thanks for the video!

[@hersheybhatt2857]

Is there a way to increase the surface tension by braking the molecule of the water? does 'hydro dynamic cavitation' ( i am talking about the cavitation in propeller) increase the surface tension, if yes, how?

[@vignan4553]

This is great! Pure concept.

[@eesha5906]

If Crash course & Khan academy had a child

[@penus7639]

Lmao the accuracy

[@coolstar7819]

😂

[@sangyunlee4523]

LAMO 🤣

[@olajumokealbert6578]

Wisdom.

[@mahnoorfatima.4]

Another Einstein! 🥸

[@kobedierckx2918]

Nice and very visual introduction of surface tension. Thank you!

[@worstoftheworst12]

Outstanding!

[@yellowsquiddyhead9198]

Great video! thank you

[@dipayanroy131]

Very informative video... Well done👍

[@talonx4266]

Only needed this one video for my science project

[@anubhutisingh9187]

Great video

[@LearnwithAGC8755]

Great Explanation

[@lildridian]

Awesome, I finally understood this

[@zeyads.el-gendy4227]

You are brilliant, sir

[@krishnaSagar69]

Very Very well explained

[@nxypps2582]

dude you are awesome! thank you this is way better than the other stuff on youtube on the subject keep it up

[@bobbleheadgary]

great explanation!! thanks so much!

[@aspektn.5066]

Seen once. Shall be seen again. Great video, as always!

[@umerabrar6843]

this video is very understandable I am satisfied

[@nikolanovakovic4150]

what a lovely explanation thanks !

[@CrashChemistryAcademy]

I'm glad you liked it!

[@AdolfoAguilarVideos]

Great video with good examples!!

[@goranblazeski6941]

You are explaining very well!! Thank you!!

[@mrtazpool]

No he didn't

[@locolainey9650]

This was great

[@tamer4456]

thanks a lot

[@junaidmughal3806]

thanks

[@staticsdynamicstechniques5800]

Excellent

[@crazyrobloxjj]

Soap: ima end this whole molecule’s life

[@TanveerAlam-oe7yt]

Good. But also related it to the above fluid also..

[@mysticalangel4629]

God bless you Wonderful video ❤

[@RaiyanTHEexplorer]

Thanks brh!!

[@SirStumblebum]

Why you gotta leave on a cliff hanger :(

[@firestormjupiter]

But i know the answer

[@amalthomas768]

@@firestormjupiter can you share it please coz I am too lazy to search it

[@DasNeueFeuer]

@@amalthomas768 This is 2 months late of an answer, so you may not need it. Nonetheless, the water strider's feet have adapted to have a very large surface area. The water's surface tension is really high - but that's in comparison to other popular liquids we know of. So the object that is capable of staying atop the water and take advantage of the surface tension must have a very high surface area to spread out the weight. The water strider does this because it has a whooole bunch of tiny tiny hairs on its thin legs.

[@amalthomas768]

@@DasNeueFeuer Hey thanks for answering. though I've found it out, appreciate the effort bro

[@JohnTaylor-nk8cp]

​@@DasNeueFeuer Nicely explained, thank you

[@bhavishyasharma7834]

Very nice explanation, god must bless you i order him to bless you now!!!

[@salamabbb]

Thanks

[@maheshgaikwad9386]

nice video

[@vedasiva695]

So if you have two beakers with different volumes of water, does the surface of the water in the beaker with larger amount of water have high surface tension compared to surface tension of lesser one? because surface tention is result of intermolecular forces right? if that is the case, if you have more wwater in the beaker u have more net downward force right ? it that how it is ?

[@CrashChemistryAcademy]

Interesting question. While a greater amount of total forces are present if more water is present, the amount of molecules (the source of the force) per unit volume remains unchanged, and so there would be no change in surface tension.

[@pranayapradhan211]

Sir u r amazing....😇😇 thanks for the explanation

[@nonutnat]

:0 thanks! Very helpful

[@BilalAhmed-si7wf]

best video

[@Flat_Earth_101]

Here's a question, does surface tension hold the center higher on a half full glass of water or does that effect only occur when the glass is full? Also is there a difference in height of the tension with different size glasses?

[@CrashChemistryAcademy]

Interestingly it is the opposite. Below the rim, the attraction between water and glass (adhesion) results in the edge of the water surface being higher. This is much more easily seen in a narrow container of glass like a graduated cylinder and is referred to as the meniscus. I do not believe surface tension correlates with the amount of surface. Surface tension can be calculated, and I would assume the calculation depends only on the type of liquid (= depends on amount of intermolecular force) rather than the total amount of surface.

[@Hematologists]

why so much negative ratings? its a great video

[@aqibtanveer9603]

Great

[@swechchhapathak7133]

🙏💕 thank u

[@bayiyingying7401]

What is the theoretical bases of surface tension?

[@gurramlokeshkumar2213]

Why there is internal pressure due to surface tension as it is counterbalanced by compression resistance of the liquid??Pls answer me

[@vihangajjar7043]

nice

[@basantimandal4864]

Great. Pure concept of surface tension. Really great. Great experiment🧐🧐🧐.

[@imrankhanimrankahn3220]

best...

[@shaktigg]

hi sir, whats said at 1:24 is incorrect, the distance between surface molecules is more than the distance between molecules below them, thats why surfave molecules have more atteaction among them that leads to surface tension .

[@nacure360]

1:16 ahhhh now it all makes sense

[@blissfulfragrance2511]

Thank you for this video! Also you speak really clearly👍

[@sabakhan-qc9di]

How can u explain capillary effect using surface tension?

[@8DMALLU]

I would also like to know that.

[@koushikyadav7362]

Sir if the pull is downward how can it bear loads (lite or heavy) instead of bearing loads it has to sink

[@CrashChemistryAcademy]

The downward pull is stopped when the repulsive force of valence electrons among the lower particles equals the downward force, at which point the two cancel out.

[@nellvincervantes6233]

And how newtons 2nd law or conservation of energy could be applied on surface molecules? They will accelerate due to downward force. And how could we prove that the molecules when tightly compressed together are in equilibrium?

[@bhavishyasharma7834]

Equilibrium means no net force, let's say we have a droplet, now at the surface of it, the molecules are attracted to inside of the surface, but because they have an extra energy(half positive), they try to pull them out. So if the surface energy is large, water molecules will try to confine in little spherical droplets because they will have more attraction

[@SM-uf9ne]

you sir, are amazing !!!!!

[@heytherecallmeskylar4738]

you could definitely work on the video quality, but the content is great: clearly and easily explained, thank you

[@CrashChemistryAcademy]

Thanks. An interesting comment since this was an old powerpoint that I dug up from years ago and made a quick video out of it. So I'll take your comment to mean that my more recent vids are better quality.... (?)

[@margaretwamaitha4532]

Yeah no doubt

[@WaqasAhmad-fx5wh]

Sir in our chem book the definition of surface tension is The surface tension is the amount of energy required to stretch or increase the surface of a liquid by a unit area Sir I think this definition is wrong cox we says that the surface molecules are compressed and they are experiencing inward pull so the surface area should be decreased not increase .Sir what do u think it should be increased or decrease.

[@CrashChemistryAcademy]

It seems the terms 'increase' and 'decrease' are not satisfactorily defined to really answer the question. Does your text define them regarding their use in surface area? If there are more surface particles crammed closer together, I guess in my mind that would mean a decrease in surface area from the point of view of individual water molecules, as well as a macro view of the aggregate water's surface: a bumpy surface would have more area.

[@bhavishyasharma7834]

Bro see, this is totally right definition because "you need a lot of energy to pull out water molecule(20kj/mol)" and that's the reason why it is confined in small droplets in equilibrium. Because they(H2O molecules) have a lot of negative energy due to attraction

[@fplej4858]

when

[@gautammure]

Brilliant!!!

[@shreeshkulkarni6953]

Sir I had a doubt how to the molecules one the surface despite of forming less hydrogen bonds forming a densely packed structure??

[@CrashChemistryAcademy]

Good question! It is not the amount of H-bonds occurring, but the net direction. The net direction of the force of H-bonds below the surface is zero, since the H-bonds are occurring in all directions. However the H-bonds occurring with surface molecules are not occurring in all directions, and so there is a net direction toward where the H-bonds are occurring, which is downward, meaning the surface molecules have a net downward force, pulling them toward a smoother surface, meaning they are coming closer together.

[@bobp8414]

A consistent explanation of surface tension has been hard to come by. See “on the cause of surface tension at a liquid-gas interface” E V Grekov , Eur J Phys 42 (2021) 055104 and references therein particularly ref 5 (fig 5) “why is surface tension parallel to the interface “

[@CrashChemistryAcademy]

Thanks for the reference!

[@WildCat1-i7x]

Amazing

[@tayp2850]

so yeah

[@doctoridk9442]

Better then Khan academy

[@studynerd7339]

why the surface molecule have more distance between the molecules below(the molecule in the bulk) , than the molecule at the side? will repulsion in each case wouldn't be same? And Sir can you explain when the surface tension is broken how do the molecules at the surface react?

[@CrashChemistryAcademy]

Any small repulsions are overcome by the large attractive force called H-bonding between water molecules, so repulsion is not really relevant. Breaking the surface tension occurs when a force greater than the surface tension physically separates the water molecules.

[@studynerd7339]

@@CrashChemistryAcademy Sir ! Thank you for the explanation and thank you again for replying after having upload the video three years ago. In other liquids where H bonding [the external factor here is not there] the molecule at the surface is equidistant from below molecule and side molecule? And does the surface molecules becomes less in number? according to your explanation the surface molecules are hesitant to go the bulk, but in the textbook it is written the molecules do become less in number at the surface? (according to thermodynamic point of view)

[@nellvincervantes3223]

The confusing part of surface tension is when applied to hydrophillic and hydrophobic surfaces when theres a surface tension on air-water interface, intefacial tension between water and solid, and interfacial tension between solid and air. So what do these terms/quantities really mean?

[@firestormjupiter]

Hydrophobic means "repels water"; Hydrophilic means "attracts water". These definitions are vague, they are what I know. For a more definitive understanding... Well the internet's out there

[@nellvincervantes3223]

@@firestormjupiter thank you sir but they are not easily to understand thats why it still confuses me. But I think the surface energy between the solid surface and air is the same as the interaction between water and solid surface. The surface energy between solid and liquid is the interaction between water molecules. And the surface energy between water and air is the surface tension when water droplet is free from contact on solid surface.

[@cesarsalcido4747]

I think that the legs of the insect send negative charge in its feet that pushes him up helping him to not sink.

[@CrashChemistryAcademy]

you are right, the negative electrons at the surface of the insect's feet are repelled by the electrons at the surface of the water. The trick is to have enough of the repulsive force to not disrupt the intermolecular attractions occurring at the surface of the water by the force of gravity. The combination of the greater surface area of the insect feet (=greater repulsion), the small mass of the insect body (less gravitational force), and the increased H2O attractions due to surface tension, allows the insect to stay above the water.

[@anantj18]

Man, he left us with a cliff hanger !!

[@yellowsquiddyhead9198]

Lmaoo ikr

[@haithamezzaddin9324]

GOAT

[@akhldwivei9425]

Nice

[@noor-e-hidyah2615]

Our chemistry teacher also sent its link 😅during online class

[@bobp8414]

Apologies. The simplified explanations given in the references may be inadequate when describing polar liquids with hydrogen bonding where there may indeed be an increase in the density at the surface . At least I think that is what papers using computer modelling show but in truth they are beyond my capabilities.

[@CrashChemistryAcademy]

Thank, I'll have to take a look.

[@ajitkumar-jx8lt]

Can solids also have surface tension?

[@CrashChemistryAcademy]

This is a great question! Interestingly, several years ago scientists found that the surface of most solids have the properties of a liquid, and in fact surface chemistry is a whole area of study in itself. So while I do not know the answer to your question, it is fun to think about!

[@denifnaf5874]

Half life was so great They named a phenomena after one of its chapters.

[@charliekwiatkowski4841]

bruh the cliff hanger is the last question on my WebQuest

[@CrashChemistryAcademy]

Pressure is force x area. So the pressure on the water's surface decreases per unit area as the area (the length of the insect's feet) increases. The less pressure, the less likely the insect will break the surface tension.

[@coolstar7819]

@@CrashChemistryAcademy Thanks for explaining!

[@atd9945]

Wouldn’t the top molucule “falls down” if it’s net force is downward?

[@CrashChemistryAcademy]

The video did not show the fact that molecules are in constant motion and are constantly changes positions relative to each other. So the surface molecules are constantly moving into the molecules below the surface, while simultaneously surface molecules are being replaced by those underneath. This happens in very fast time frame. However, the net effect of all this is that due to that downward force, new molecules at the top will be less spread out than they were in other locations. All throughout the water the molecules are pulled in all directions, but the moment they reach the surface they are only pulled downward.

[@atd9945]

@@CrashChemistryAcademy thanks for the answer! It’s crystal clear

[@parulaggarwal9405]

D insect's enjoying life 3:10

[@accsamhi1401]

Lol today my teacher give this link for best visitations

[@shifaalhattali7844]

👌🏼👌🏼👍🏼

[@elwlrma_2720]

Why stop uploading? Ur stoichiometry video really helped me! I am sure others agreee too...why stop?

[@CrashChemistryAcademy]

Too much grading!! I'll get on it this summer. Thanks much for your comment.

[@elwlrma_2720]

Crash Chemistry Academy If possible, how about make a video about stoichiometry in acid and base (pH and titration)

[@elwlrma_2720]

Crash Chemistry Academy Thankyou

[@bobp8414]

This explanation is incorrect, the density of particles at the surface is less than in the bulk but the forces between the molecules at the surface and parallel to it are larger,hence the surface tension at the surface and parallel to it.

[@GokulJS-vb2rd]

Water striders use surface tension to their advantage through their highly adapted legs and distributed weight

[@CrashChemistryAcademy]

Yes!

[@aleksandr_berdnikov]

According to this explanation, an air bubble in the bulk of the water would be expanded by surface tension, not compressed as it is IRL...

[@CrashChemistryAcademy]

The compression occurs due to pressure from the weight of the water

[@aleksandr_berdnikov]

@@CrashChemistryAcademy I am talking about the surface tension pressure, $2sigma/r$, that is independent of gravity. Pressure in the water that is being compressed (by weight of upper layers or any other means) is a separate independent thing. Say the bubble is in 0-gravity, like, on a space station. Or even better, a soap bubble. The gravity there is negligible, and the pressure inside provided by the inner and outer surfaces of the film add up, not cancel each other out, as your model would imply.

[@marija347]

Hey! I your videos have really helped me, but I have some trouble understanding concepts that you haven't got content about, so I was wondering if you could give me your email for me to ask you some questions? I'd really appreciate your tutorials, and I would love to have you as a mentor! :)

[@josejaimefelixgarciagarcia8884]

Why is it called surface tension when the surface experiences compression

[@CrashChemistryAcademy]

maybe it has something to do with the surface being pulled down, like high tension wires are pulled laterally. (?)

[@os7944]

Term tension is nothing but pull force...as in surface tension the surface molecules experience pull force so it is named as surface tension

[@pcbeauty2696]

what an ending... lmao. Thnx for the lesson....see ya

[@CrashChemistryAcademy]

Seeya! Thanks!

[@Anaghaaaaaaa]

Razor blade kept horizontally in water floats sue to surface tension whereas when kept Vertical, it sinks. But why?

[@CrashChemistryAcademy]

The force from the weight of a single razor is concentrated in a tiny surface area when vertical, resulting in a large force per unit area, enough force to break through the surface tension. When the force from that same weight is spread over the much much larger surface area when horizontal, then there is much much less force per unit area, less than is needed to break the surface tension. It is the same concept as lying on a bed of nails, if that helps.

[@Anaghaaaaaaa]

@@CrashChemistryAcademy Thank you😍😍☺

[@CrashChemistryAcademy]

@@Anaghaaaaaaa You're welcome!

[@PAUTNETER]

Thats Whats Up!!!

[@Ajax2696]

And yet we haven’t been able to create force fields smh.

[@simonkehoe2676]

If you have an ice cube 🧊 and smash it into a trillion pieces. It would behave completely differently than water at room temperature. If you heat water to steam the molecules separate and the volume increases 1600%. No surface tension.

[@AXAXAXAYt]

Liquid lover