Why is soap so slippery? asks Laryssa Ouro-Rodrigues, a student in Brookville, NY.
Stepping on a bar of soap is more risky than stepping on a banana peel-but only if the bar is wet. Open up a bar of Ivory or Dove or Dial, and it’s unlikely that the dry bar will shoot out of your hand and land on the bathroom floor. But add water, and voila: your soap has leapt into the air, landed behind the sink, and is covered in a fine layer of grit and cat hair.
Why do soap and water make such a good team? Soaps are surfactants, “surface-active agents” that turn down the surface tension of water. Surfactants actually make water wetter, by weakening the attraction between the water molecules. Which is a good thing, if you’re looking to get clean.
The basic recipe for soap is fat or vegetable oil plus an alkali solution, such as lye. Think of soap molecules as tiny tadpoles, with round “heads” and narrow “tails.” The heads have a negative electrical charge. Likewise, water molecules have a slight positive charge on one end. Since (electrical) opposites attract, the soap molecule heads are hydrophilic–water lovers.
Read the rest of this entry »
How come when you eat sour candy you make weird faces? asks Danielle Vollono, a student in Brookville, NY.
It’s how we decode dinner: Scientists say there are at least four basic tastes — sweet, salty, sour and bitter. (Some add a fifth, umami, the savory taste provided by an amino acid in food called glutamate.) While we have generally pleasant reactions to sweet and salty tastes, it’s a different story with “bitter” and “sour.” “Bitter” may mean poison, so our brain is hard-wired to reactive negatively to the taste. “Sour” may mean a food is spoiled, and full of harmful bacteria.
When given a taste of something bitter, newborn babies make an immediate expression of disgust, and turn their faces away. But when tasting something sour, like lemon juice, an infant’s reaction is usually slower and milder. The lips purse and pucker, the nose wrinkles, the eyes narrow. Over a period of seconds, the baby may close her mouth and retract her lips, or frown.
But as babies get a few months older, some may actually smile at the taste of lemon juice. Human beings seem to have a love/hate relationship with sour tastes, even at 4 months old. Which is why some of us enjoy endless varieties of sour candy — and lemons — even as we pucker our lips and scrunch up our face.
Read the rest of this entry »
How come your funny bone is called your funny bone? asks Noah Kennedy White.
If you’ve ever hit your funny bone, you know that the only amusement comes from the faces, gestures, and sounds you make as you grab your elbow and dance around the room. The vibrating pain, extending to your fingers, seems to start in the knobby bone on the inner elbow. Actually, the bone is an innocent bystander; it’s a nearby nerve that’s causing all the excruciating commotion.
It should be called the Funny Nerve, but its official name is the ulnar nerve (after the ulna bone in the forearm). Stretching from neck to hand, the ulnar nerve sends impulses back and forth from the spine.
The pain from hitting the ulnar nerve is no laughing matter. Smaller nerves running through the skin allow us to sense heat and cold, or to feel the prick of a thorn before it pierces the skin. These nerves are relatively unprotected, so that we can perceive the world around us. But the ulnar nerve is a big nerve. Its main function is to control muscles in the forearm and hand, as well as enabling our pinky and ring fingers to feel sensations.
Other large nerves are protected by bone and fat. But the ulnar nerve is almost completely exposed. The ulnar nerve runs in a bony groove (the “cubital tunnel”) through the elbow, where all that stands between desktop and nerve is an thin layer of fat and skin.
Read the rest of this entry »
How come human beings have appendixes if they don’t need really them? asks Kayla Winchester, a student in Manhasset, NY.
The appendix. Can’t live with it, can’t live without it.
Oh, wait.
Actually, the appendix is one of the body’s most unobtrusive organs. No painful protests, like the ungrateful stomach after Thanksgiving dinner. No gasping after a sprint to the finish line, courtesy of the overworked lungs. And no ominous rumbling, like intestines encountering the wrong restaurant tomato. And not only can we live nicely with an appendix, we can also live happily without one, if need be.
Did nature simply get sloppy and produce a worm-like cave on the large intestine? Recently, researchers at Duke University in North Carolina unveiled a new explanation for the appendix’s existence. Hint: Rather like the fire extinguisher that usually sits unused on the wall, this tiny organ may be good in a crisis.
Read the rest of this entry »
How do they make paper? Is it always made from trees? asks John David Ketchum, age 6, of Phnom Penh, Cambodia.
In August, it seems like we’re surrounded by paper. Before the start of a new school year, stores aisles are blocked by stacks of notebooks, binder paper, construction paper, and Post-it notes. Once school starts, there’s more paper: forms to fill out, exams to take, reading lists to take home.
But while most of the paper around us was made from wood, the paper we pay for it with wasn’t. Whether it’s a one-dollar bill or a hundred-dollar bill, U.S. paper currency is actually 75 percent cotton and 25 percent linen. So the folded-up money in our wallets is made from fibers usually spun into fabrics. Which explains why you can throw your laundry in the washer, dry it, and pull a still-usable ten out of your jeans pocket. (A tiny care label on each bill might help.)
Read the rest of this entry »
How come your hands get all wrinkled after they’ve been in water? asks Kelsey Steck, a student in Holtsville, NY.
While nearly everyone gets pruny fingers after a long bath, their exact cause is still a mini scientific controversy.
Part of the explanation involves how skin responds to water. While skin is a good protective covering for our bones and organs, it isn’t waterproof. In fact, skin is nourished and plumped up by water, even absorbing it from the air around us.
The skin’s outer layer, the epidermis, is attached to the thicker layer underneath, called the dermis, but there is some “give” between the two. Hair follicles in the dermis pump out sebum, an oil that protects and lubricates the skin. But the undersides of fingers and toes (as well as palms and soles) don’t have hair, and don’t have as much protective oil.
Read the rest of this entry »
|