| The Columbia Encyclopedia, Sixth Edition. 2001-07. |
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| fluid |
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| any substance that is able to flow. Of the four states of matter, only a solid is not a fluid, since it has a definite shape that is not readily changed. Any liquid, gas, or plasma is classed as a fluid. |
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| | | The Columbia Encyclopedia, Sixth Edition. Copyright © 2007 Columbia University Press. |
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