General knowledge - questions and answers. If you have a question about this topic, please click on the "New Question" button. If you wouldn't like to miss any new question in this topic, please subscribe.
Like absentmindedly drumming on a tabletop, idly running a finger around the rim of a glass can make a kind of music—an otherworldly, ghostly music. How come?
Even if your family groans when you sing along to the car radio, even if you didn’t make the cut for the choir, and even if you got asked to be the drummer rather than the lead vocalist in your friends’ garage band, you sound exactly like your favorite pop (or opera) star in the shower. How come? And why do we enjoy singing in the shower to begin with?
There’s an official name for the horrible sounds that emanate from a blackboard: chalk squeal. Scientists say that the explanation involves both friction and resonance.
When you hold a large seashell to your ear, you can hear a distant roaring sound. It’s as if the great rumble and crash of the ocean waves is somehow trapped within the shell. So when you bring a seashell home from the beach, it keeps the memory of the sea alive. But even if you don’t have a seashell handy, and it’s too cold to go to the beach, you can always hear the ocean. Just pick up an empty coffee mug, and hold it to your ear, tilted slightly away. Ah, there it is—the gentle, echoing roar of the waves.
Have you ever stood on a city sidewalk and heard the distant wail of an approaching fire engine? As the fire truck comes into view, the sound of its siren becomes louder and more frantic, the wail higher and higher pitched. Then, as it passes, the opposite effect occurs: The sound of the siren drops in pitch, getting lower and lower as the vehicle vanishes into distant traffic. But the fire truck’s driver hears no such change; to him, the siren that he flipped on 20 blocks ago has sounded at a steady pitch.
We’ve all seen it in movies or old TV westerns—as the stagecoach (or train) picks up speed, its fast-moving wheels appear to switch direction, slowly turning backward. We also occasionally see the phenomenon in real life, with spinning car tires and whirling ceiling fans. Scientists call it the Wagon-Wheel Effect. What causes the “backward” effect?
In Lewis Carroll’s Through the Looking Glass , Alice (of Alice’s Adventures in Wonderland fame) discovered that a mirror was a doorway to a parallel universe, where everything is reversed—and anything might happen. While mirrors aren’t really an entry to another world, they are very curious objects. A mirror seems to reverse left and right—making newspaper headlines and T-shirt slogans read backward, and flipping the image of your face and body. But a mirror doesn’t flip top and bottom—we don’t appear in a full-length mirror with our head at the bottom, feet and floor at the top.
Ah, summertime. Season of cookouts, fireworks, road trips, and mirages . . . like that cool, shimmering pool of water on the highway ahead on a scorching-hot, drought-dry day. Mirages can be even more spectacular in Earth’s coldest regions. Take a trip to the Arctic, and if conditions are just right, you may see an upside-down iceberg, seemingly hanging in the air above the sea.
Remember Superman’s X-ray vision? His eyes shot X-rays at a door; the beams bored through, and he could see what his enemies were up to on the other side. Only doors made of lead could foil Superman. Lead is a good shield against X-rays. That’s why we wear heavy lead aprons at the dentist’s office. But Superman’s X-ray eyes came from the imagination of his creator. Eyes can’t shoot beams of light. Our eyes see when light from other sources, like the Sun, is reflected back from an object. However, X-rays are indeed a kind of light—a kind that is invisible to us. X-ray light has a lot more energy than visible light. That’s how it can penetrate wooden doors—or skin and muscle.
When an animal’s eyes glow green or yellow in the headlights, it’s a sign of good night vision. A special layer of cells in the back of the eye reflects light back like a mirror. Some of that light is reabsorbed by the eye, letting a deer, raccoon, or opossum see better in the dark. But human eye-glow doesn’t lead to anything but weird-looking birthday photos—Mom, Dad, and little Billy leaning over the candle-studded cake, all with gleaming red eyes. If a camera steals your soul, perhaps a flashbulb replaces it with something demonic.
Ever take a swim in the ocean, and notice that your hair and your swimsuit both look darker? As you walk back to your beach chair, you notice your wet feet leave dark footprints in the sand. As you dry off, your towel darkens, too. But it’s not just seawater that does the trick. Pelting raindrops can turn your plain white shirt into a polka-dotted mess. Rinse off the sidewalk with a hose, and you’ll see the white cement turn gray. You can even use the narrow stream of a hose to write your name on the driveway. Many porous objects—paper, fabric, tree bark, soil, hair—darken as they are doused in (clear) water. How come?
Where do rainbows come from? William Wordsworth, an English poet who published his first sonnet in 1787, wrote: My heart leaps up when I behold A rainbow in the sky . . . Something about seeing a rainbow gives us a shivery feeling. The bands of color, dipping down from the sky, are so beautiful and rare. People once thought rainbows were signs from the gods. It’s not surprising. A rainbow appears in the sky, seemingly out of nowhere. Then, just as mysteriously, it vanishes.
How are shadows formed? In Peter Pan by J. M. Barrie, Peter loses his shadow when Nana the dog grabs it as Peter escapes out a window. Finding the shadow, Nana’s owner, Mrs. Darling, rolls it up and puts it in a drawer for safekeeping. Real shadows are more ephemeral. Try to grab a shadow, and your hand will simply pass into its shade. Try to jump on your own shadow, and it jumps with you, ever connected to your feet.
Bright yellow flames on the birthday candles studding an iced cake. Dusky blue flames circling the burner of a gas stove. Dancing yellow-orange flames crackling over wood in the fireplace, with flashes of red, green, and blue. Fire comes in a rainbow of colors, some rarely seen outside a science lab.
On a sunny day, the sky is blue, the clouds white, and the Sun a normal, if a bit boring, yellowish-white. But at sunset, white clouds and blue sky turn pink and orange and purple, and the Sun glows orange red.