why does a swimming pool appear blue?

[her34]

if you've ever seen an empty pool you'll see that the plaster is white. yet when filled with water it appears blue. why?

 

[ChineseGuy]

because the water is reflecting the sky which is blue

 

[The Boston Dangler]

Water absorbs light at differing frequencies and rates. The blue is absorbed less. Just like the sky.

 

[gordanfreeman]

Originally posted by: ChineseGuy
because the water is reflecting the sky which is blue

what about indoor pools

 

[ChineseGuy]

hehe.. my bad... The sky is blue because earth's water, and water is blue because of post # 3 by The Boston Dangler

 

[her34]

Originally posted by: The Boston Dangler
Water absorbs light at differing frequencies and rates. The blue is absorbed less. Just like the sky.

if it's simply a property of water, then why is a glass of water clear or a white styrofoam cup of water appear white like the cup?

 

[The Boston Dangler]

The effect builds very gradually. A cup holds a helluva lot less water than the pool. There's all kinds of reflecting and refracting going on. By the time the light zigzags it's way out of the pool or ocean or sky and into your peepers, it's blue. I bet a totally mirrored pool would have a more pronounced effect. It would also be wicked cool.

 

[Jeff7]

Originally posted by: The Boston Dangler
The effect builds very gradually. A cup holds a helluva lot less water than the pool. There's all kinds of reflecting and refracting going on. By the time the light zigzags it's way out of the pool or ocean or sky and into your peepers, it's blue. I bet a totally mirrored pool would have a more pronounced effect. It would also be wicked cool.

Same reason why a single sheet of acrylic looks perfectly clear, but if you have a stack of them, not much light gets through. Each one absorbs a little bit of light - same with water. As light has to pass through more of it, some of it is absorbed. Water simply absorbs blue light less readily than other wavelengths.

 

[BespinReactorShaft]

But why exactly is blue absorbed less? Something to do with blue being on the short-wavelength end of the EM spectrum? How do we explain this on the (sub)atomic level?

 

[Loki726]

Originally posted by: ming2020
But why exactly is blue absorbed less? Something to do with blue being on the short-wavelength end of the EM spectrum? How do we explain this on the (sub)atomic level?

Light (in the form of phtons) hits the h2o atoms. These photons have distinct amounts of energy that correspond to the different frequencies of light (as given by the planck relation). High frequency light has more energy. Now these h2o atoms have electrons orbiting them, these electrons can ONLY exists at certain energy levels. When a photon hits an atom, it will ONLY transfer its energy to the atom if the energy of the photon is exactly equal to the energy required for an electron to change energy levels. Since there are only specific energy levels, only photons with certain frequencies will be absorbed.

In this case, the frequency of blue light does not correspond to the difference between any two energy levels of the water and therefore it is not absorbed.

 

[The Boston Dangler]

this is from sciencemadesimple.com

http://www.sciencemadesimple.com/sky_blue.html

 

[bsobel]

Originally posted by: ChineseGuy
hehe.. my bad... The sky is blue because earth's water, and water is blue because of post # 3 by The Boston Dangler

Your 0 for 2 now.

 

[The Boston Dangler]

Ya like the way I put up a link that totally proved me wrong? lol

 

[BigPoppa]

Originally posted by: The Boston Dangler
Ya like the way I put up a link that totally proved me wrong? lol

Better than people who insist on being right yet being shown evidence to the contrary.

:thumbsup:

 

[shortylickens]

I dont want to take away from the science here, but if the pool is chlorinated, most chlorine also has a blue dye.
Some companies use green.

If the pool color is really rich, that means they overdid it. If its too pale, it might mean there is not enough. (Every state has rules for how much is needed in a public pool).

The color is just an easy way of seeing the amount.

EDIT: I suppose you could put laundry bleach in, just to see for yourself.

 

[DrPizza]

Chlorine leaves the pool, entering the air. Does the dye leave at the same rate? Otherwise, the dye cannot be used to monitor the level of chlorination.

 

[NorthernSink23]

Answer on a sub-atomic level: http://www.dartmouth.edu/~etrnsfer/water.htm

Googled for: "Why is water blue?"

 

[shortylickens]

It isnt used to monitor, legally you need to have an actual chlorine monitor.
But it helps. And I think the dye may leave with the chlorine, but since it should be automatically replenished you would never know.

 

[The Boston Dangler]

The chlorine in pools usually isn't dyed, maybe you're thinking of toilet cleaner? 18 years of having my own pool, and 3 years in the pool industry, and I've never seen chlorine (solid granules or liquid) blue or green. Clorox or other laundry type bleaches are not sufficient concentration to chlorinate a pool of any size. They also may contain detergents or other chemicals, super bad for pools. Chlorine level testing can only be done with a test kit (fill a test tube with pool water from arm's length below the surface, add a couple drops of mystery juice, shake, match the color to the supplied chart)

Besides, are the skies and oceans super chlorinated?