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Speaker 1: Brain Stuff is sponsored by Harry's dot Com. Get a

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Speaker 1: quality of the shave is so important that Harry's purchased

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Speaker 1: the factory that makes their blades. Fifteen dollars gets you

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Speaker 1: Go to Harry's dot com use the code brain stuff

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Speaker 1: to say five dollars off your first purchase. Welcome to

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Speaker 1: brain Stuff from how stuff works dot com where smart happens.

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Speaker 1: Hi Am Marshall Brain with today's question, what makes glass transparent?

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Speaker 1: Glass is so common that most of us take it

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Speaker 1: completely for granted. But just what is it about glass

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Speaker 1: that makes it transparent? Why can't we see through a

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Speaker 1: window but not through the wooden frame that surrounds it.

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Speaker 1: Scientists are still researching this question, but here's one way

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Speaker 1: to think about it. You've probably noticed that most liquids

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Speaker 1: and gases are transparent water, cooking oil, rubbing alcohol, air,

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Speaker 1: natural gas, and so on. Our are all clear. That's

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Speaker 1: because of a fundamental difference between solids, liquids, and gases.

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Speaker 1: When a substance is in its solid state, normally, its

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Speaker 1: molecules are highly organized in relation to one another, strengthening

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Speaker 1: the bond between them and giving the substance rigidity. The

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Speaker 1: atoms are not moving around freely. As the substance changes

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Speaker 1: from a solid to a liquid, however, the strength of

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Speaker 1: the bond lessons and the molecules begin to align themselves

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Speaker 1: randomly and they can also move around. If we follow

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Speaker 1: the substances progression to a gas, we see that the

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Speaker 1: molecular bond is greatly weakened and the relationship of the

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Speaker 1: molecules to one another is almost completely random. This progression

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Speaker 1: from ordered to random organization is the primary reason that

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Speaker 1: light can pass through liquids and gases. Just like bricks

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Speaker 1: are stechnically on top of one another, the ordered molecules

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Speaker 1: of most solids are virtually impenetrable to light waves. Depending

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Speaker 1: on the substance, the light waves will be reflected, scattered, absorbed,

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Speaker 1: or more likely some combination of the three. But as

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Speaker 1: the substance changes to a liquid or gas, and the

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Speaker 1: molecules are not stacked neatly anymore, gaps and holes occur

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Speaker 1: that allow portions of the light waves to pass through.

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Speaker 1: The greater the amount of randomness of the molecular organization

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Speaker 1: of the substance, the easier it is for light to

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Speaker 1: pass through. Although forms of glass such as obsidian a

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Speaker 1: volcanic glass can occur naturally, glass is generally a man

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Speaker 1: made substance. Here's the basic way to make glass. You

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Speaker 1: take the most common glass material, silicon, which is just

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Speaker 1: plain old sand like you would find on the beach.

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Speaker 1: You heat it to an extreme temperature until it becomes liquid,

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Speaker 1: and then you cool it. The resulting substance has a

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Speaker 1: molecular structure that's very random, like a liquid, yet that

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Speaker 1: retains the strong bond and rigidity of a solid. A

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Speaker 1: similar method called quenching is used with plastics to make

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Speaker 1: them transparent or translucent. Quenching causes the polymers, the long

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Speaker 1: chain molecules in the plastic to settle into a random

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Speaker 1: pattern that allows light to pass through. You can even

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Speaker 1: use this process with organic substances. Clearer or translucent candy

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Speaker 1: is created by heating the ingredients of the recipe and

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Speaker 1: then rapidly cooling them. Notice that clear glass, clear plastic,

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Speaker 1: and clear candy are all solids that are melted and

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Speaker 1: then cooled. It's the same kind of process. Do you

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Speaker 1: have any ideas or suggestions for this podcast. If so,

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Speaker 1: please send me an email at podcast at how stuff

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Speaker 1: works dot com. For more on this and thousands of

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Speaker 1: other topics, go to how stuff works dot com and

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Speaker 1: be sure to check out the brain Stuff blog on

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Speaker 1: the how stuff works dot com home page. Brain Stuff

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Speaker 1: is sponsored by Harry's dot com. Get a great shaving

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Speaker 1: experience for a fraction of the price. The quality of

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Speaker 1: the shave is so important that Harry's purchased the factory

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Speaker 1: that makes their blades. Fifteen dollars get you a set

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Speaker 1: that includes a handle, three blades, and shave cream. Go

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Speaker 1: to Harry's dot com use the code brain stuff to

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Speaker 1: save five dollars off your first purchase.