You all need to know this!

Fascinating. :)

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

 
I want some of the mic stands he was using.

 
I wonder if anyone told the kids that this exactly how the atmosphere works?

 
 
Didn't they do that experiment in the Gulf of Mexico  a few years back? 

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.     

 
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.
 
 

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
 
 

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."
 
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
 
 

 
Mike, the main reason why the Earth's atmosphere doesn't float off into space is the same reason we don't float off into space - gravity.
 
Incidentally, I deliberately italicized 'float' because there are a number of other factors that could explain why a planet might lose it's atmosphere, but these factors would have to exert a force on the atmosphere's gaseous atoms and molecules greater than the pull of gravity holding them there.
 
Again, my memory is a little rusty on this, but I'm pretty certain outside influences such as the solar wind (a constant stream of charged particles emitted by the sun) can react with atmospheric particles and give them enough kinetic energy to reach escape velocity. The Earth's magnetic field (which extends out into space around the planet) actively repels the solar wind (electrical charge and magnetic force are essentially the same thing) preventing most of the harmful particles from reaching our atmosphere.
 
Most of the solar wind is diverted around the Earth, but some of the charged particles are trapped and deposited in radiation belts, the most well-known of which are the Van Allen belts. When these trapped and highly energetic charged particles collide with atoms of the upper atmosphere, some of the energy released is dispersed as light (of many different wavelengths, depending on the energy released) and we see this as a display of aurora. Aurora are normally associated with the Earth's polar regions as these regions are where the magnetic field is strongest. 
 
To create a planet's magnetic field, the major factor is that its iron core has to be molten - the movement of the charged particles in this physical state generates the field.
 
It's generally thought that the solar wind was the major factor in Mars losing its atmosphere. Mars once had a molten magnetic core, and its atmosphere was protected from the solar wind in much the same way as ours is. However, as Mars's mass is only around 10% of that of the Earth, its core was under significantly less pressure (and consequently temperature) and so its core solidified around four billion years ago. Without the protection afforded by a magnetic field, Mars's atmosphere was exposed to the solar wind and has been eroded away ever since.

mike_mccue
BTW Steve,
 I just went off and read about Gravitational force. It gets over my head real quickly.

Are you upside down?

What I want to know is:
 
Where is Howard Wolowitz from the Big Bang Theory?
 
Once he sees this, he'll be able to wash the marks put on his face by the others.

Hi Steve, Thanks very much for taking the time to put all that into perspective and make it seem understandable.
 
Hi Dave,
 What can I say? Your explanation has exceeded my optimism. Thanks for taking the time to lay out the framework for a comparison/contrast of attractive forces and especially for going to the trouble of quantifying the effects of gravity.
 
 When you first mentioned the 97% my *intuition* reacted with a short burst of "how can that be?" but then I realized that I was confusing myself by not accounting for the effects of barometric pressure and by simply thinking about gravity.
 
 I can't make a sensible excuse, because it doesn't make sense. I was distracted by the idea that air pressure lowers rapidly with altitude and now recognize that the weight (I hope I use the correct word there) of any single molecule doesn't change with the same schedule.
 
 Your explanation about the temperatures and kinetic energy is fascinating.
 
 Thanks for entertaining my interest in this subject... I've always found it very interesting and try to understand as much as can as a lay person.
 
 You have made it very easy to have learned a greater appreciation of the subtleties.
 
 I don't think I can thank you enough. Thanks!
 
 
 best regards,
mike

Hi,
 
Such a wonderful physics lesson ... it's awesome!
 
Kids could use seeing that and learning a thing or two!