Hi Dave,
 It just occurred to me that surface tension is not "exactly" how the atmosphere works.
 
 We've got some gravity happening too.
 
 Can you elaborate or perhaps compare/contrast the phenomenon of gravity and surface tension at a layperson level?
 
 
best regards,
mike
 
 

craigb
Very cool!
 
(But violent bodily expulsions are still discouraged.)

 
Speaking of which (if I ever go into space) and seeing how the water just "attached" itself to his hands (looking like some sort of clear gel), I hope that when using the facilities.......... there's  going to be some sort of gravitational force that weighs it down.     

It's called a vacuum cleaner.
 
:-)
 
 

 
Mike, surface tension has nothing to do with gravity or atmosphere.
 
Surface tension, can easily be demonstrated as the 'skin', or meniscus that forms when you pour water into a clean glass. Once the water settles, the edges of surface that touch the glass will appear to 'climb' up the side. The effect is similar to capillary action - where water will rise up inside a thin tube against the force of gravity (and when the tube is open ended, so it's nothing to do with atmospheric pressure).
 
The effect is more visible when you fill the glass to the top - as you reach the apparent total capacity of the glass, you'll find that as you carefully keep on adding water, the surface will form a discernible bulge. So, effectively, the meniscus of the water is strong enough to prevent the water escaping (by gravity) over the side of the glass. So, with water, you could actually have a 1 pint glass holding more than 1 pint of water. Once there is enough water in the glass for the gravitational force to exceed the surface tension, the water will overflow.
 
If I remember correctly, this property of water is caused because the molecules of H₂0 aren't physically symmetrical, or more pertinently - electrically symmetrical. With a simple molecule of water, you might expect the three atoms to bond in a straight line: H-O-H so the molecule would naturally configure itself into the lowest energy state possible. However, due to the electrical properties of the molecule, the structure has two spare pairs of electrons in the outer valence shell (these are referred to as 'lone' pairs).
 
As the two hydrogen atoms are electrically positive and the two lone pairs are negative, they repel and attract each other just as the poles of a magnet would and the lowest energy state of the molecule is therefore not a straight line, but more akin to a slightly distorted tetrahedron, with oxygen at the centre and the two hydrogen atoms at two of the points.
 
This makes the water molecule 'polar' - where there is a different electrical charge at either 'end' of it.
 
It is this polar nature that allows nearby molecules of water to become loosely attracted to each other - i.e. the lone pairs of one molecule are attracted to the hydrogen atoms of another.
 
It is this attraction that causes surface tension.
 
I'm pretty sure (but far from certain!) that the polar nature of water is exploited by soaps and detergents. I recall soap molecules being hydrophobic (repelled by water) at one end and hydrophilic (water 'loving') at the other. It is this property that helps 'dissolve' oil and grease in water as the hydrophobic ends of the soap molecules bury one end of themselves into the fat and help disperse the globules.
 
Anywho, it's something like that. It's definitely related to why, if you have an 'over-filled' glass of water with a meniscus on top and add a drop of detergent to it, the surface tension is destroyed, and the glass will immediately overflow.
 
 

Science: It's what's for breakfast.

Thanks Steve,
 
It's the commonality of the notion of "attraction" that I am wondering about.
 
There are some forces within an atom that keep it acting like an atom.
 
There are forces that make atoms stick together like molecules.
 
There are forces that make molecules stick together as in compounds.
 
It seems like some of these forces have something in common.
 
I am certainly just working with a lay persons understanding of the most basic aspects of it.
 
Thanks for sharing your insights.
 
 
best regards,
mike
 
 

BTW Steve,
 I just went off and read about Gravitational force. It gets over my head real quickly.
 
 Now I think that the answer to my question may be something like. Gravitational force is very tiny compared to electromagnetic force. Maybe something like that?
 
 I guess where I am second guessing myself is in questioning what keeps the atmosphere stuck to the globe. Why doesn't the gas get sucked over to the Sun? Is it electromagnetic force keeping the *air compound* (if you will) in proximity to it's other molecules? Is it simply the Earth's gravity? It seems like, out at the edge of "space" that the gas must be nearly weightless... and that is why I jumped to the conclusion about surface tension playing a role.
 
Then I felt foolish for making such a bold statement.
 
 
all the best,
mike
 

Jeff Evans
What happens when you wring out a very wet cloth in space!
 
http://apod.nasa.gov/apod/ap130424.html
 
 

Thanks Jeff. It isn't what I expected at all. Amazing... I imagine that weightlessness gives a whole new meaning to having your "heart in your throat".

 
J

As with any interpretation of naturally occurring events, the models that we use to explain them have levels of interpretation.  I think the best way to answer your question about a common force without invoking a quantum mechanical model for the atom (or molecule) is to say that to a large extent we can interpret interactions in terms of electrostatic interaction (or opposites attract).
 
The term intermolecular interaction is used to describe the interaction between two (or more) distinct molecules.  The strength of the interaction between the particles (here I use the term particle to stand for either an atom or molecule) will govern its physical properties.  Is the material a liquid or a gas at room temperature?  If you have 2 different liquids, why do they boil at different temperatures?
 
The structure of a molecule (or in other words, the way its atoms are arranged) will govern the way it interacts with other molecules.  So, different structures ultimately give rise to different types of intermolecular interactions.  The different types of intermolecular interactions vary greatly in their attractive strength and chemists have fancy names for these different types of interactions. 

"As with any interpretation of naturally occurring events, the models that we use to explain them have levels of interpretation."
 
This was very hard for me to learn as a school boy. I desperately wanted the target to stay put but it seems like, as you are becoming more sophisticated in your understanding, that you have to abandon simpler models that you thought you understood and work with more complex models.
 
I think a class on that subject, alone, would have been very helpful to me.
 
It took a long time to realize what was happening. Habits relating to your understanding need to be changed but it does not come naturally.
 
Thanks for explaining what you have.
 
Should I assume that the question about "why doesn't the atmosphere float off into space" is simply too complex to describe in a format such as a forum post?
 
Is that sort of what you meant when you explained this?:
 
"The structure of a molecule (or in other words, the way its atoms are arranged) will govern the way it interacts with other molecules.  So, different structures ultimately give rise to different types of intermolecular interactions.  The different types of intermolecular interactions vary greatly in their attractive strength and chemists have fancy names for these different types of interactions."
 
Thanks again for taking the time.
 
best regards,
mike