What is a Fluid?

Ocean waves off the coast of Mexico
Click on image for full size (136 KB JPEG)
Image copyright 2002 University Corporation for Atmospheric Research
The short answer is that a fluid is a gas, a liquid or a molecules around but not without mixing them up. That's what we mean when we say a fluid can't support a shear stress. Jupiter is made of gas and a gas is a fluid.

Much of the universe is made of fluid, including planetary oceans, interstellar clouds. Even rock and metal can be fluid if they're hot enough to be molten; that's what happens deep inside the Earth.

Fluid dynamics (also called fluid mechanics) is the science of how fluid moves around. A fluid in motion is called a flow.


Is Air a Fluid? Classroom Activity

What is a Fluid?

Ocean waves off the coast of Mexico
Click on image for full size (136 KB JPEG)
Image copyright 2002 University Corporation for Atmospheric Research
A fluid is anything that would spill or float away if it weren't in a container (unless it's big enough to be held together by gravity like a star). If you can stir it up with a spoon or blow it through a straw, it's a fluid. Water is a fluid and so is air. In fact, all liquids and gases are fluids. In space and inside stars there's also another kind of fluid called a molecules in a solid are stuck together, but in a fluid they're free to move past each other. So if you had very small hands you could push one molecule of a fluid one way and another molecule the other way and off they would go in the direction you pushed them.

Much of the universe is made of fluid, including Earth's oceans, giant planets like Sun, and huge deep inside the Earth.

Fluid dynamics (also called fluid mechanics) is the science of how fluid moves around. A fluid in motion is called a flow.


Is Air a Fluid? Classroom Activity

What is a Fluid?

Ocean waves off the coast of Mexico
Click on image for full size (136 KB JPEG)
Image copyright 2002 University Corporation for Atmospheric Research
When you hear the word Fluid you might think of a liquid like water or juice - something that you can stir up with a spoon. That's right - all liquids are fluids. But did you know that gases like air are fluids too?

If you can stir something up with a spoon or blow it through a straw, it's a fluid. Actually, all liquids and gases are fluids. In space and inside stars there's another kind of fluid called a rain, the Earth's oceans, giant gas planets like Sun, and huge **RELATED_LINK_TITLE** -->

Is Air a Fluid? Classroom Activity


Page created September 26, 2005 by Mark Miesch. Last modified November 2, 2005 by Jennifer Bergman.
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