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Author Topic: Why is snow white ?  (Read 6852 times)

Offline Pappy

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Why is snow white ?
« on: 21/10/2003 18:55:51 »
My 7 year old daughter asked, "Where does all the white go when the snow melts?" Formulating an answer in terms a 7 year old can understand is somewhat of a challenge. Anyone up for it?


 

Offline NakedScientist

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Re: Why is snow white ?
« Reply #1 on: 21/10/2003 19:39:16 »
Well, firstly less consider why snow is white in the first place.

Snow is frozen water. But as we all know water is transparent, so why is it white when it freezes ? The answer is  exactly the same reason that glass is transparent but the stuff it's made from - sand - isn't.

Sand and Snow are made of crystals of a cooled liquid - water in the case of ice, and silica in the case of sand. The crystals of both have many surfaces so light hitting them bounces around all over the place, and a large amount is reflected back at you, which is why it looks white.

When the snow melts, becoming liquid water again, light can pass straight through, without much reflection, and hence the whiteness disappears.

A nice way to demonstrate this principle is to make some soap bubbles. An individual bubble - a bit light a pane of glass - is transparent. But make lots of small bubbles and put them together and they look white because the light hitting them is being bounced about between them like it is by the ice crystals in snow, making the bubbles en-masse look white.

Hope this explains it.

TNS
 

Offline Ians Daddy

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Re: Why is snow white ?
« Reply #2 on: 21/10/2003 20:39:15 »
Pappy, Your daughter asked a good question. These kids are very curious. I'm pleased that they are.

TNS, once again, you've so eloquently educated me. Thanks again.
 

Offline Pappy

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Re: Why is snow white ?
« Reply #3 on: 21/10/2003 20:52:55 »
Naked.......ah, yes, bubbles, great idea! The next time she has a bubble bath I'll remember to address her question again. We'll isolate one bubble, then scoop up a hand full of bubbles and compare! Thanks, that's something she can relate too.
 

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Re: Why is snow white ?
« Reply #3 on: 21/10/2003 20:52:55 »

 

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