How can liquid nitrogen be so cold but not freeze into a solid? asks Michael Chapman, a student in Holtsville, NY.
Solid, liquid, or gas? Many things are solids at room temperature and normal air pressure — like a chunk of iron, or a stick of butter. Others are liquid — like water, or olive oil. And still others are gases–like oxygen or nitrogen. The universe is full of substances that behave differently at normal atmospheric pressure and temperature here on earth.
Fast fact: While we depend on oxygen for our very life, oxygen isn’t the main gas whizzing around in the air. Earth’s air, in fact, is 78 percent nitrogen gas.
The “boiling point” is the temperature at which a substance turns from liquid to gas. Water’s boiling point is 212 degrees F. We can turn water to gas — steam — by putting a pan of it on the stove to heat. Eventually, the water will begin to bubble, and we’ll see steam escaping into the air. The water has changed from one state — liquid — to another: gas.
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Which came first, the chicken or the egg? asks Jessica Bolz, a student in Melville, NY.Chicken or egg? Like a hall of mirrors at the carnival, each attempt at an answer just leads to another question. If the chicken came first, then didn’t it hatch from an egg? And if the egg came first, wasn’t it laid by a chicken? It’s one of those questions that seem unanswerable.
Scientists agree on where chickens came from: In a sense, human beings invented them, just like they invented cows and pigs and other domesticated animals on Old MacDonald’s Farm.
If chickens were interested in tracing their family trees, they would need to bone up on some DNA research done in Japan. Every chicken that ever lived can trace its ancestors, say researchers, to a particular subspecies of Red Jungle Fowl in Thailand.
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How come it is still light for an hour after the sun sets? asks P. Ramana Mohan, of India.Twilight time: a time of purple clouds, deepening shadows, a fading glow in the sky. Still light enough to play outside, but getting harder and harder to read without a lamp. As a song made popular by the group The Platters in 1958 goes, “Heavenly shades of night are falling; it’s twilight time.”
Twilight usually refers to the time just after the sun sets in the evening. But it also can mean the time just before the sun rises in the morning. During twilight, although the sun is hidden below the horizon, the sky is still aglow with light, gradually dimming (after sunset) or intensifying (before sunrise).
During twilight, the light for our evening activities comes courtesy of the upper atmosphere.
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Why do leaves change color in the fall? asks Patricia Brown, of New York City.Autumn’s cool days are trimmed with deep blue skies and golden light, and brilliant leaves of yellow, orange and red. Leaves changing color in the fall are a tree’s way of preparing for long winter, rather like we put up storm windows and pull warm clothes and blankets out of storage.
In summer, the leaves on trees like pin oaks and sugar maples are green because they are chock-full of the green pigment chlorophyll.
Trees need sunlight to produce chlorophyll. In turn, chlorophyll uses sunlight’s energy to split water (H2O) into hydrogen and oxygen. Meanwhile, leaves also absorb carbon dioxide gas from the air. The end products of leaf chemistry: carbohydrates (homemade plant food for the tree), and oxygen, released into the air (the gas we need to breathe). The whole process is called photosynthesis.
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Why does water expand when it cools? asks B.M. Vignesh Babu, of Madras, India.Water is peculiar. When most substances change from liquid to solid form, they shrink together, become denser, their molecules packed most closely together.
But when water changes from a sloshy liquid to solid ice, it expands, becomes less dense. Which is why ice floats to the top of your Coke, rather than sinking like a stone to the bottom.
At normal atmospheric pressure, molecules usually behave in predictable ways as their temperature changes. Molecules fly apart into a gas when heated, condense into a flowing liquid when cooled, and shrink into a frozen solid when chilled still further. The changes in state parallel changes in energy: from high energy to medium energy to barely jiggling.
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Why do elephants have trunks? asks J. Navarrete, a student in Woodside, NY.Imagine life with a trunk: Sniff a friend’s sandwich, then grab it with your nose. Reach for something on a high shelf without standing on a chair. Swim across a pool underwater, using your long nose as a snorkel.
There are no bones in an elephant’s trunk, making it as supple as a garden hose. A trunk has more than 40,000 muscles and tendons, and its tip is covered with nerve endings. In addition, there are one or two “fingers” on the tip to grasp small objects. Like a monkey’s tail, a trunk is “prehensile,” and can be wrapped like a rope around an object such as a branch. Unlike a monkey’s trail, an elephant’s trunk can weigh 400 lb. and measure 7 feet long.
All of this makes a trunk flexible (it can hoist a log), strong (the log can weigh more than 300 lb.) and precise (it can pick up a penny lying flat on the floor).
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