Jahanshah Javid

the truth of the matter is that the bellboy didn't cheat them...

He decided that he'd charge a $2.00 transport fee for services rendered.  Furthermore! he did't have a calculator and could not divide $5.00 evenly 3 ways which would have been $1.66 with 2 pennies left over... and 2 cents is a crummy tip by any standard so that's where the dollar went!!!    :-P

Ali A Parsa, I wonder if you went to Alborz

and had a younger sister called Fati?

Anahid

divaneh, transparency is a Good thing..

where I come from.  Happy to have you with us.

Ari jan, thanks for all the good discussion about glass

Ari jan, you really are into your science mode today.  I know howstuffworks may not be perfect answer but we are on IC, not in a Solid State class.   Personally, this branch of science is one of my favorites and not to brag, I did get an A in Solid State my senior year in university, but I am simlpy not in my science mode/mood tonight.  Sorry to disappoint you by including a comment that was excerpt from howstuffworks.  Fortunately, you took it few notches above and now everyone who has followed this comment thread, has learned a lot more.  Thanks.  I need to read this thread more carefully too.

Seeing thru a wall

Divaneh, Ari's explanation of relative sizes of scatterers in a material to the wavelengths of electromagnetic (EM) wave incident on it suggests that we may all be x'parent or opaque to certain kinds of EM waves.  Radio waves (which are the kind of EM waves that radio & TV signals are carried on) have such large wavelengths, that a brick wall is x'parent to them (which is why we have over-the-air radio & TV).  So you may be able to "see" someone thru a brick wall:  //www.youtube.com/watch?v=ifQkbMJ_sXM&fmt=18  On the other hand, a wall of conducting materail, such as iron, would block radio waves, as well.

Still not clear

I read through all those comments and still don't know why I am transparent to others.

Good examples maqshush

For the reader,

If you insist on a brick wall metaphor, imagine each brick being spherical with a mirror-like surface, like a perfectly shiny ball bearing. Then stack these ball bearings in a box as in an orange crate. The ball bearings are analogous to atoms and their being mirrored is anlagous to the atom not absorbing the light but scattering it. Now if you did this with normal sized ballbearings you wouldn't see any light coming through because as maqshush points out the light waves get scattered all over the place. But if you reduce their size until they become much smaller than the wavelength of light (light wavelength is roughly 1/200 of human hair thickness) something magical happens. The scattered wavelets synchronize their motion so that they add up to the same shape as the original wave. In other words, the information contained in the original wave (the image)  is not lost (scattered) but stays in one piece. This information-preserving behavior is responsible for what we call tranparency. Letting all the light come through in a jumble isn't enough (that is called translucence, as in frosted glass). A transparent material preserves the order of the incoming wave. This is possible because light (as with all wave/particles in the universe) has an intrinsic clock which allows it to exhibit time-synched behavior. The technical term is "wave interference."   

What r u chasing in each direction?

Ali Parsa, the depth difference between the shallow & deep ends of your pool is not as much as I assumed it might be (I thought it may be a good 15' at the deep end).  So my guess about effects from the pool floor is probably not plausible.  What is peculiar about the numbers you mention is the variation going deep-to-shallow but not the other way.  The variation of 70 to 90 is comparable to the difference between the 2 directions.

Can you try w/o any kickoffs against the pool wall?  E.g. start by lying flat on water and just push forward by swimming (no push from wall)?  May wanna have someone observe you from outside. I assume you've checked for water possibly coming (or sucked in) thru walls.  Also, do the more attractive ladies (or gentlemen, as the case may apply) happen to congregate at the deep end rather than the shallow end?

Tear down that brick wall

Analogous to the examples Ari gave to counter the stacked-brick conjecture, you can make others.  The crushed vs block ice example is analogous to color of snow.  Snow flakes are arrangements of snow crystals, which are basically ice crystals wrapped around speck of dust.  Ice, like water, is fairly transparent (x'parent), but when you pack 'em together like in a snow flake, the light that goes through each crystal or in between crystals gets all scattered about among these crystals, so that what is seen is just white light. 

Similar thing with glass vs pile of sand.  Glass is mostly liquified and then cooled silica sand (w/ a couple other ingredients so as not to make it brittle).  But pile of sand isn't x'parent.  That's again b/c the light that goes thru each x'parent grain of sand and the light that goes between sand particles are all scattered about in the pile (in addition to impurities in pile of sand).  In any case, the stacked-brick conjecture, as I understand it, doesn't address the issue.  True, a wall of stacked bricks blocks light, but the question is then why does each brick block light.  

And the answer, as I see it and said below, has to do with the atomic structure of glass, which is not excited by the energy of visible light, so bound electrons in glass reemit the light they absorb and it "passes through."  UV light would excite glass molecules and so would be largely absorbed ("blocked").

Good curve ball, Azadeh

Eureka, eureka!

Cloud and steam are colloidal, which is a state where liquid phase and gaseous phase are mixed! Hence the relative opacity! Hee Hee! :-)

Azadeh

Azadeh, testing your hypothesis

OK, throw me another curve ball. 

Ari

You know, on a second thought, I think it is the *temperature* that creates the opacity of steam (cold or hot temperatures.) As for the ice cube, I hypothetise that both the pressure and the change in temperature (due to crushing) are responsible for its opacity - by condensing its molecular structure.

Azadeh

Ari, steam, water, in that order :-)

Hi Ari,

I think the steam is harder than water to see through because its molecules interact with air's (oxygen and other stuff.) I imagine that in a vaccum enclosure, such thing wouldn't happen to it. We can always send you to that enclosure with your oxygen mask on to see if I'm right :-).

Azadeh

Anahid, try this "experiment."

Ali A Parsa

I'm guessing it won't though; the jar would just sink mostly straight down. But eliminating suspects is part of catching the criminal who steals your lap speed. By the way, 60 strokes seems like a lot for the average pool.

Still learning

Thank you Anahid. Very helpful. I'm learning more and more :)

Here is answer from howstuffworks about why glass is transparent

Dear JJ, I saw your blog and it is interesting. However, I have not had time to participate in it.  I just saw your last comment which indicated that you still have not seen a satisfactory answer.  I googled "Why glass is transparent" and I saw the following response which is from howstuffworks.

//science.howstuffworks.com/question404.htm

I am going to make the more important parts in underline. Here is the answer from howstuffworks and I hope it helps:

"Glass is so common that most of us take it completely for granted. But just what is it about glass that makes it transparent? Why can we see through a window and not through the wooden frame that surrounds it?

You have probably noticed that most liquids and gases are transparent. Water, cooking oil, rubbing alcohol, air, natural gas, etc. are all clear. That's because of a fundamental difference between solids, liquids and gases. When a substance is in its solid state, normally its molecules are highly organized in relation to one another, strengthening the bond between them and giving the substance rigidity. As the substance changes from a solid to a liquid, however, the strength of the bond lessens and the molecules begin to align themselves randomly. If we follow the substance's progression to a gas, we see that the molecular bond is greatly weakened and the relationship of the molecules to one another is almost completely random.

This progression from ordered to random organization is the primary reason that light can pass through liquids and gases. Just like bricks stacked neatly on top of one another, the ordered molecules of most solids are virtually impenetrable to light waves. Depending on the substance, the light waves will be reflected, scattered, absorbed or, more likely, some combination of the three. But as the substance changes to liquid or gas and the molecules are not stacked neatly anymore, gaps and holes occur that allow portions of the light waves to pass through. The greater the randomness of the molecular organization of the substance, the easier it is for the light to pass through.

Another factor happens at the sub-atomic level. The atoms that bind together to make the molecules of any particular substance have electrons, usually lots of them. When photons come in contact with these electrons, the following can occur:

• An electron absorbs the energy of the photon and transforms it (usually into heat)
• An electron absorbs the energy of the photon and stores it (this can result in luminescence, which is called fluorescence if the electron stores the energy for a short time and phosphorescence if it stores it for long time)
• An electron absorbs the energy of the photon and sends it back out the way it came in (reflection)
• An electron cannot absorb the energy of the photon, in which case the photon continues on its path (transmitted)

Most of the time, it is a combination of the above that happens to the light that hits an object. The electrons in different materials vary in the range of energy that they can absorb. A lot of glass, for example, blocks out ultraviolet (UV) light. What happens is the electrons in the glass absorb the energy of the photons in the UV range while ignoring the weaker energy of photons in the visible light spectrum. If the electrons absorb the energy of any portion of the visible spectrum, the light that transmits through will appeared colored according to the portion of the spectrum absorbed. In fact, the color of any object is a direct result of what levels of energy the electrons in the substance will absorb!

Although forms of glass, such as obsidian or volcanic glass, can occur naturally, Glass is generally a manmade substance. Here is the basic way to make glass:

• Take the most common glass material, silica, which is just plain old sand like you would find on the beach.
• Heat it to an extreme temperature until it becomes liquid, then cool it.

The resulting substance has a molecular structure that is very random like a liquid yet that retains the strong bond and rigidity of a solid. This is a simplification of the process. Usually you add both a substance to make the silica melt quicker and something else to stabilize it so that the glass is not brittle and easily broken. The temperature, heating time and cooling method must all be very exact.

The materials used for glass-making cool to form an amorphous mix of molecules (like a liquid) and have electrons that do not absorb the energy of photons in the visible spectrum. This is why you can see through glass, but not wood, metal or stone, which are all solids.

A similar method, called quenching, is used with plastics to make them transparent or translucent. Quenching causes the polymers (long-chain molecules) in the plastic to settle into a random pattern that allows light to pass through. You can even use this process with organic substances. Clear or translucent candy is created by heating the ingredients of the recipe and then rapidly cooling them.

Notice that clear glass, clear plastic and clear candy are all solids that are melted and then cooled. Same process!

Thousands of different substances are used to make various forms of glass. How much and what type of light is transmitted depends on the type and purity of the substance used. Silica, in its purest form, transmits light well. Very little of the light wave is absorbed, but some of it is usually reflected. Look at almost any window and you will see this is true.

Other materials used to make glass may transmit or block specific types of light, such as ultraviolet light, or even parts of the visible spectrum. You have probably seen glass that was black or some other opaque color. Most often the color is caused by microscopic particles suspended in the glass, like the impurities we talked about in some liquids and gases. Another way to change the properties of the glass, such as filtering specific wavelengths of light, is to slow down the cooling process enough to allow the molecules to partially crystallize, or form pattern. And finally, some materials are chosen because they can be shaped and made to transmit and/or refract light in specific ways to use, for instance, as eyeglass lenses or as a magnifying glass."

Relatively speaking

hamsade ghadimi, yes, glass isn't invisible. But we're talking in relative terms. Compared to a wall, a window IS invisible. That's the whole point of my blog. I'm trying to understand why glass is transparent and most other things are not.

But thanks for the reminder :)

jj

answers to your questions: 1) glass is not invisible, 2) not enough. :)

JJ's java

You know what ,JJ? It's all your fault. This site is so @#!$ addictive (excuse my French )which didn't let me wait for my Saturday morning coffee before jumping in.

What missing dollar?

Mirza, the case of the missing dollar was widely analyzed and resolved here:
//iranian.com/main/blog/capt-ayhab/math-r...

I don't want a wife like you!, Mina

I called it "undisputedly" for smarty girls like you. It's famous for the rest of us!! Just google it.

//mathforum.org/dr.math/faq/faq.missing.dolla...

Mirza

Why is this the most famous math problem? 

25 + 3 is 28 not 27.

Undisputedly, the most famous math problem

Three men go to stay at a motel, and the man at the desk charges them $30.00 for a room.They split the cost ten dollars each. Later the manager tells the desk man that he overcharged the men, that the actual cost
should have been $25.00. The manager gives the bellboy $5.00 and tells him to give it to the men.

The bellboy, however, decides to cheat the men and pockets $2.00, giving each of the men only one dollar.

Now each man has paid $9.00 to stay in the room and 3 x $9.00 = $27.00. The bellboy has pocketed $2.00. $27.00 + $2.00 = $29.00 - so where is the missing $1.00?

Thnaks maqshush, Ari and Monda

Here are the answers I can provide to your pertinent questions:

The pool is a regular one with depth of 4' at the shallow end to about 5.5 ' at the deep end. Starting is the same-with a simple kick against the wall of the pool behind me at take-off. No diving. Total strokes needed to complete the lenth varies from 60 to 90-with almost consistently 60 from shallow end to deep end, but always over 60(70-even 90) from the deep end to shallow end. Although collection of more statistical  data is pertinent and more scientific, I really do not want to carry it that far and I would be more than satisfied and thankful with the best explanation I can get with the information I thus far have. Thank you all for your help. A.P.

khody

going off the deep end

AAP, how real & reproducible is your alleged pool delay phenomenon?  How much of a difference is it anyways?  Is your start the same from both ends?  E.g., similar kickoff or dive?  You may be getting different effects from the boundaries of the pool during takeoff.  At the deep end the floor of the pool is far away and it's only the pool wall that acts as a hard boundary during kickoff, while at the shallow end reflection or absorption of waves off of the floor during kickoff may not be negligible.  Post a detailed contour map of the pool and the data set you've meticulously collected.  Then repeat the experiment while snorkling.

U c thru glass b/c you ain't a b

A more transparent explanation for the transparency of glass may go as follows.  As I think was mentioned below, besides the light that may pass through the material w/o interacting with its constituent particles (much less likely in a solid), light may be thought of as either absorbed, reflected or transmitted by the electrons in a solid.  Reflection occurs when free electrons are available to move around the solid.  B/c when an electromagnetic (EM) wave (which is what light is) accelerates a free electron, typically the electron radiates 2 component EM waves of its own, one in the direction of the initial EM wave but in a manner that mostly cancels it, and one in the opposite direction of the initial wave, which constitutes the reflection.  Glass doesn't have much free electrons, so you only get a bit of reflection by glass.  

Electrons bound in atoms can only be excited to certain energy levels depending on the atomic structure of the material.  A bound electron can be excited to an available energy level if the particle of light, photon, that it absorbs matches the correesponding energy difference.  (Typically, this would result in heating of the material.)  If this is not the case, then the electron will reemit the absorbed light, in which case the material appears transparent.  Visible light does not have the right energy to excite the bound electrons in glass, so it's just reemitted and "passes through" the material.  On the other hand, ultraviolet light has the right energy to be absorbed by glass, which is why sun tanning behind glass is more difficult.  So, to creatures who can see ultraviolet light, such as birds & bees, glass appears more opaque than it does to us.

Which is why this commercial 

//www.youtube.com/watch?v=iqKS-hkhhh4&fmt=18 is not really an effective advertisement.  The crows are laughing b/c to them it's almost as if the dumb guy were trying to go thru frosted glass in front of us.