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Author Topic: Surface Tension !..what is it ?  (Read 15623 times)

Offline neilep

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Surface Tension !..what is it ?
« on: 04/07/2006 15:25:37 »
Surface tension is a remarkable thing....allowing insects and messiahs to walk on water.:)

But what is it ?..is it the compaction of water molecules caused by the air pressure ?

Does salt water have surface tension ?...what about other liquids ? milk , oil, fruit juice etc etc.

How thick is surface tension ?..is it dependent on the temperature ?

If one was able to remove the water beneath the surface tension...would it be a pliable sheet ?...would that even be possible ?...is that what bubbles are ?...balls of surface tension ?

Sorry for all the questions :)

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another_someone

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Re: Surface Tension !..what is it ?
« Reply #1 on: 04/07/2006 16:36:48 »
Without going out to wikipedia to get a definitive answer, I shall quickly try and explain my understanding.

It is down to the difference between a liquid and a gas.

In a gas, the molecules of the gas are all bouncing around freely, largely ignorant of each other except when they happen to bump into each other.

In a liquid, because the molecules are slower, and more closely packed, they actually get influenced  by each others electrical fields.  This glues the molecules closer together, and it is this glue effect that causes the water molecules to stick together so much that an insect can walk over them without pushing them apart.

This electrical force is the same force that causes molecules to form rigid crystals, but in liquid form the molecules are still jiggling about enough that they do not create rigid structures, but the electrical force is still proving enough glue between the molecules to keep them bound together in a loosely packed liquid.

This electrical force is true of all atoms and molecules to some extent.  It is very little true of helium, which is why it is so difficult to liquefy helium.  It is particularly strongly true of water.  A water molecule is actually lighter than diatomic oxygen (the normal form of oxygen in the atmosphere), or diatomic nitrogen, or carbon dioxide.  All other things being equal, it should be more difficult to liquefy water than it is to liquefy oxygen.  It is only because the extraordinarily strong electrical dipole of water that means that water is actually a liquid at temperatures and pressures where all the other heavier molecules remain in gas form.



George
« Last Edit: 04/07/2006 17:34:38 by another_someone »
 

Offline neilep

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Re: Surface Tension !..what is it ?
« Reply #2 on: 04/07/2006 16:54:42 »
THANK YOU GEORGE.

I realized I could have gone to Wiki too but then that would have negated the nature of this site and I truly wanted the answer.

I will now follow it up by investigating further and appreciate your answers.

I would not offend your modesty by awarding you a star but if there is one person who is consistent, displaying eloquence and articulation in their contributions and demonstrating a field of knowledge far and wide in their scope here........ it is you.

I am sure I am not alone in thinking that.......though I realise...you'd rather be not here earning some dosh sir !!!

I am sure you would be most welcome on many a quiz panel !

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Offline Soul Surfer

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Re: Surface Tension !..what is it ?
« Reply #3 on: 05/07/2006 09:00:49 »
Another someone.  OK as far as it goes but you forgot to mention that because the molecules stick together as a bulk,  when you get to the surface there is some residual stickiness between the molecules that tends to make the surface a bit stronger stuck together than the bulk material.  That is also why very tiny amonts of contaminants can have a profound effect on surface tension because you only need a sincle layer of molecules (like detergents or oil) to change the effective surface tension of the water.

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Offline Hadrian

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Re: Surface Tension !..what is it ?
« Reply #4 on: 05/07/2006 12:50:28 »

And I used to think that surface tension was the feeling you got when you walked into a room after an augment had just taken place.

 



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ROBERT

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Re: Surface Tension !..what is it ?
« Reply #5 on: 05/07/2006 15:47:43 »
quote:
Originally posted by neilep

Surface tension is a remarkable thing....allowing insects and messiahs to walk on water.:)

Does salt water have surface tension ?...what about other liquids ? milk , oil, fruit juice etc etc.

How thick is surface tension ?..is it dependent on the temperature ?

If one was able to remove the water beneath the surface tension...would it be a pliable sheet


Water has a very high surface tension compared with similar liquids, e.g. it it three times that of ethanol.
The surface tension on water it is strong enough to support a metal paperclip:-

(I placed a grid in front of the light to create the "contour lines" which show the deformation in the surface of the water).


Surface tension is dependent on temperature:-
http://www.engineeringtoolbox.com/water-surface-tension-d_597.html

It is necessary to lower the surface tension of water before it becomes a "pliable sheet" = thin film.

The "black hole" in the above image is not a hole, it is a region of soap film which is thinner than the wavelength of light, (a few tens of nanometers thick).

« Last Edit: 05/07/2006 16:14:20 by ROBERT »
 

Offline neilep

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Re: Surface Tension !..what is it ?
« Reply #6 on: 05/07/2006 16:11:39 »
Robert.......those are amazing images...THANK YOU VERY VERY MUCH..

Big Hugs to you and Ian...oh..I suppose to that green font monster dude Hadrian too !! :)

That is Incredible about the film being thinner than the wavelength of light...amazing !!!

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« Last Edit: 05/07/2006 16:12:51 by neilep »
 

Offline Hadrian

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Re: Surface Tension !..what is it ?
« Reply #7 on: 05/07/2006 16:19:50 »
Its not true


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Offline neilep

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Re: Surface Tension !..what is it ?
« Reply #8 on: 05/07/2006 16:29:35 »
LOL....well, you don't need to go the dentist...though i would recommend some eye drops !!..but..apart from that...you're quite the looker !!

nice ears !!

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Offline Karen W.

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Re: Surface Tension !..what is it ?
« Reply #9 on: 08/07/2006 05:19:38 »
Great pics guys, You guys are such a crack up!
« Last Edit: 08/07/2006 13:45:44 by Karen W. »
 

Offline Hadrian

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Re: Surface Tension !..what is it ?
« Reply #10 on: 08/07/2006 17:43:18 »
You should see me when I get mad!    

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Offline eric l

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Re: Surface Tension !..what is it ?
« Reply #11 on: 01/08/2006 18:38:04 »
Instead of talking of "surface tension" we should call it "interfacial tension", because there is not only the tension between the liquid en air (or another gas), but also between the liquid and any other substance it is in contact with (e.g. the glass, metal, plastic or whatever of the vessel or tube).
When we consider only the interface between liquid and air, we find there is a close relation between surface tension and boiling point.  Water (H2O) has a very high boiling pint when you compare it to NH3, HF of H2S, because it behaves like a polymer (due to hydrogen bonds).  and indeed we see that water has a high surface tension.  
This relation between surface tension and boiling point can be explained through vapour pressure :  if a molecule of a liquid passes from the liquid into the surrounding atmosphere (=evaporates)there is for a moment a small increase in the surface.  When vapour pressure is high (and we are close to the boiling point) the energy needed for this increase in surface is available, and los of molecules can evaporate.  When we are well below the boiling point, this energy is not available, and the surface has to be kept smooth.
 

Offline fabrizti

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Surface Tension !..what is it ?
« Reply #12 on: 08/10/2008 11:32:00 »
Hello
I have seen video about surface tension measurement and treatment
on this site: newbielink:http://www.boussey-control.com/en/surface-tension/index.htm [nonactive]
 

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Surface Tension !..what is it ?
« Reply #12 on: 08/10/2008 11:32:00 »

 

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