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[MUSIC]

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JOAN CARTAN-HANSEN, HOST:

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There are four basic

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states of matter: solid, liquid,

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gas, and plasma.

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When matter changes from one

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state to another, it's called a

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phase change.

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So, what causes a phase change?

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Well, there are a few different

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things.

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One is to change the

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temperature.

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Make it cold and water turns

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from a liquid into a solid.

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Turn up the heat and water goes

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from a liquid into a gas.

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Pressure can also change

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matter's state.

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Deep in the earth, the solid

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rock is under a lot of pressure.

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But as the rock moves toward the

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surface, the pressure drops and

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the temperature changes.

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So solid rock turns into liquid

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magma.

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On the other hand, if you take

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carbon dioxide gas and put it

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under high pressure, it turns

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into a solid called dry ice.

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Water, by the way, is the only

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abundant compound on earth that

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regularly goes through phase

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shifts from solid to liquid to

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gas and back.

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Other compounds make the shifts,

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but not as easily as water.

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For more information about

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states of matter, check out the

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Science Trek website.

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You'll find it at

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science trek.org