Archive for the ‘physics’ Category
Why do things made of rubber bounce? asks Khiana Lowe, a student at Long Island Lutheran Middle and High School in Brookville, NY.
If you’ve ever tried dribbling a wooden ball, or attempted to shoot a piece of string across the room, you know there’s something different about rubber. Rubber, whether natural or manmade, is very elastic. An elastic material is one that can be stretched to several times its own length without breaking – and then snap back to its original size.
Bouncy is just another word for highly elastic. And rubber is very, very bouncy. Natural rubber is made of long, flexible chains of carbon atoms, connected here and there to hydrogen atoms, coiled up into a tangled mass. In plastic, another material whose molecules are arranged in long chains, the chains are rigid. But rubber’s chains can twist and flex. When a piece of rubber stretches, the molecular chains uncoil; when the rubber is released, the chains retract, curling back into place.
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How does a boomerang return to the person who threw it? asks Rajendra Singh, of Jaipur, India.
Baseballs don’t. Footballs don’t. Even frisbees don’t. But boomerangs do–come back, that is.
If boomerangs were a new toy on the market–just invented–there would probably be a boomerang craze going on. Everyone would rush out and stand in long lines to be the first on the block to have one.
But in fact, boomerangs are very old. People were playing with the come-back toys thousands of years ago.
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What causes quicksand, and where is it found? asks Edward McClarty, of San Francisco.
Unless you’re on Gilligan’s Island, roiling pits of dangerous quicksand aren’t found around every bend in the trail. There are a lot of myths about quicksand, among them:
Quicksand sucks you down like a vacuum cleaner. In fact, quicksand doesn’t pull you down any more than a swimming pool does. Quicksand is more buoyant than water, so it’s actually easier to float in quicksand than in a swimming pool.
Quicksand is a bottomless pit. Most patches of quicksand are a few inches to a few feet deep.
Quicksand is always made of sand. In addition to sand, clay, swamps, and silt can all become what scientists call “quick.”
By now you might have guessed that what we call “quicksand” is more of a phenomenon than a thing. The phenomenon is “quickness,” the way water flowing through sand, clay, or other material lifts and separates its small grains.
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How come you can still see a star that disappeared many years ago? asks Rebecca Herskovits, a student in Yeshiva Har Torah, Bayside, NY.
Human beings are fascinated with the idea of a time machine–a way to shake off the bonds of the present and travel into the past or the future. No one has ever made a time machine, and scientists say it may be impossible–the very nature of the universe may prevent such “travel.”
But the sheer size of the universe means that light carries information from the distant past into our present, showing us what the cosmos looked like long, long ago and far, far away. When we look into the night sky–or even at our own Sun–we are seeing the past, not the present.
Here’s how it works. Light, the speediest thing we know of, zips along at 186,000 miles a second in the vacuum of space. Light leaves the surface of a star or planet, travels a great distance, and finally enters our eyes. We see the star or planet as it was–not as it is.
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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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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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