the answer files

Why is the sky blue?

What is lightning?

What are the states of matter?

Does hot water freeze faster than cold?

Why does a can of Coke sink while a can of Diet Coke floats?

Why do you close your eyes when you sneeze?

Why do mosquitoes bite me more than my friends?

Why do your feet stink?

How does gravity work?

How fast does the space shuttle move in orbit?

What is escape velocity?

What would happen if you turned on your headlights while moving at the speed of light?

What are the states of matter?
Matter comes in five phases, or states. Three are familiar, one is uncommon, and one is a freak of nature that exists only when atoms have virtually stopped moving -- at almost absolute zero. We'll take them from the coldest to the hottest:

  1. Bose-Einstein condensates exist in a weird condition where all the atoms attain the same quantum-mechanical state. Although it exists only within a whisker of absolute zero, the condensate may some day be used to make atomic lasers or super-accurate clocks.

    resist

  2. Solids are materials with a definite volume and shape. They resist forces that tend to deform them: think ice, steel, or your computer screen.

  3. Liquids are relatively incompressible materials that take the shape of their containers and have a free surface, but do not expand indefinitely: think liquid water, beer or soda.

  4. Gases expand to fill their containers, and usually have relatively low density: think steam, oxygen and laughing gas.

  5. Plasmas are ionized (electrically charged) gases with a similar number of positive and negative charges: think arc welding, fluorescent lights, and the sun.
hot air

Did you know?
Like water, many substances change from solid to liquid to gas when heated. Some substances, however, take a shortcut. Carbon dioxide, for example, "sublimates" directly from solid to a gas. That's why dry ice is handy for shipping: it doesn't melt into a liquid but rather sublimates into a gas that can be vented to the atmosphere.

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The Why Files
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