The inability to hear, or deafness, can occur for many reasons. Some types of hearing loss result from something blocking sound as it travels from the outer ear to the eardrum and the tiny bones in the middle ear. Other types of loss arise from damage to or a defect of the inner ear or the auditory nerve, which is the nerve that carries sound signals from the inner ear to the brain. Deafness can happen as a result of disease, including severe ear infections, or it can be inherited, with the deafness being apparent at birth or sometimes showing up years later. Injuries and accidents also account for many cases of deafness.
Extremely loud noises, like those that come from an explosion, can cause deafness, though that loss of hearing is sometimes temporary. People who work in noisy factories or those who are frequently exposed to very loud music can also develop hearing loss over time. Many people gradually lose some or all of their hearing when they reach old age, but some of those types of hearing loss can be overcome by wearing a hearing aid, which makes noises like speech or music louder.
Babies are born with about 300 to 350 bones, but many of these fuse together between birth and maturity to produce an average adult total of 206. Bone counts vary according to the method used to count them, because a structure may be treated as either multiple bones or as a single bone with multiple parts. There are four major types of bones: long bones, short bones, flat bones, and irregular bones. The name of each type of bone reflects the shape of the bone. The shape of the bone also tells about its mechanical function. Bones that do not fall into any of these categories are sesamoid bones and accessory bones.
Paint coats wood, protecting it from sunlight and rain damage and making it last longer. When early farmers had enough money to paint their barns, they usually used inexpensive paint because the structures were so large. Ferrous oxide, a chemical powder that gives paint its red color, was readily available and cost little. Thrifty farmers in New England, New York, and the upper Midwest region painted their barns red. In those places, red barns remain a tradition. But there are plenty of barns in other parts of the country that are not red. Early farmers that were poor—especially in regions like Appalachia and the South—left their barns unpainted because they did not have the money to do the job.
Unpainted wood usually weathers to a soft gray color. And in places like Pennsylvania, Maryland, and some southern Midwestern states, the most frequently seen barn color is white. Some people think that white barns grew popular when dairy farming became more important after the Civil War; white suggests cleanliness and purity, desirable qualities to be associated with milk production. Special farms where fancy horses or prize livestock were raised sometimes had barns painted unusual colors, like yellow, green, or black.
Every country has a national flag, including the United States. Flags date back to around 1000 B.C.E., when the Egyptians used primitive versions of flags—some were even made out of wood or metal—to identify themselves and to signal to others. Ships started using flags at sea to signal to each other and to harbors, often to let them know they had a diseased crew aboard. Flags are still used today to let sailors know what weather conditions await at sea. The military also made use of flags to rally its troops. During the ancient wars, capturing an enemy’s flag was considered an honorable seizure.
Today, the most popular use of flags is to identify and symbolize the world’s countries, which became commonplace in the 1700s. When new lands are discovered—and, for example when Mount Everest and the Moon were conquered—explorers raise their country’s flag as a sign of their being the first to set foot on these unchartered lands.
Tall, multistory structures called skyscrapers are made of steel, which is sturdier and lighter in weight than other building materials, such as brick and stone. In the late 1800s, when steel production became common, architects experimented with steel, forming it into long, thin pieces called girders. The first skyscrapers, built in the United States in the 1880s, were constructed using vertical columns and horizontal beams made from steel girders. This supporting skeleton allowed buildings to rise to 10 or more stories. Skyscrapers grew taller when designers began using bundled steel tubes instead of heavy girders.
Tube buildings, like Chicago’s Sears Tower, get most of their support from a stiff grid of steel columns and beams in their outer walls. The lighter weight pieces need less support, and so architects can 144 add more height. Additional beams can be placed diagonally for additional support while adding little extra weight. The girders and beams are bolted together and welded on all sides so that the building will not sway from side to side as a unit when there is wind.
Early in human history, people used anything that they could find to keep their teeth clean. Usually a thin, sharp object, like a stick, was used to pick out food left between teeth. Chewing on the end of certain sticks would fray the wood, making a kind of brush, which could then be rubbed across the teeth. (Even today, members of primitive tribes chew sticks to keep their teeth clean. The constant chewing produces more saliva than usual, which helps wash food away.) Later, people found that if they rubbed abrasive elements, like salt or chalk, across their teeth, they could get rid of grime. They also used water and pieces of rough cloth to clean their teeth. Toothpicks made of all kinds of materials also became popular. Rich people had jeweled toothpicks made of gold and silver. Toothbrushes for the wealthy, with fancy handles and hog bristles, came into use in the eighteenth century.
Only much later, when cheaper, woodenhandled toothbrushes were made, and the importance of good dental hygiene became known, did most people start to regularly use them.
The custom of proclaiming wedding banns began in 800 AD when Roman Emperor Charlemagne became alarmed by the high rate of interbreeding throughout his empire.
He ordered that all marriages be publicly announced at least seven days prior to the ceremony and that anyone knowing that the bride and groom were related must come forward. The practice proved so successful that it was widely endorsed by all faiths.
Libraries offer books for people of all ages, and much, much more—they are places of learning and discovery for everyone. Besides books, public libraries offer videos, DVDs, free access to computers and the Internet, and many literacy-related programs.
For elementary school children, there are variations of the read-alouds and storytelling hours that often include discussions and presentations by the children themselves, as well as summer reading programs. For middle-school kids, there may also be book talks, summer reading programs, creative writing seminars, drama groups, and poetry readings. The more you read, the more you learn! In addition, the library is a place to find information and help with schoolwork. Your school library may offer some of these services as well.
Dogs bark to communicate with other dogs and with humans. Dogs are descendants of wolves, which are social animals that live in packs, and they share many of the behaviors that define the complex relationships that exist within such animal groups. Few domestic dogs live together in packs (though they often consider their human family their group), but they still use complicated behaviors that involve smell, sight, and hearing to communicate. A dog has many scent-producing glands that it uses to communicate. The scent that a dog leaves behind (in its urine, feces, and paw prints) can reveal its sex, age, and even its mood to other dogs that come sniffing by.
A dog uses its posture, facial expression, and ear and tail position to communicate with other dogs, too. And it uses its voice to communicate by whining, growling, howling, or barking. A dog usually whines or whimpers when it is in distress: when it is hungry, cold, or in pain. Growls indicate that a dog is angry and ready to fight. Barks usually show excitement.
In the early days of theatre, the players were lit by gas lamps hidden across the front of the stage. Early in the twentieth century, it was discovered that if a stick of lime was added to the gas, the light became more intense, and so they began to use the “limelight” to illuminate the spot on stage where the most important part of the play took place. Later called the “spotlight,” the “limelight” was where all actors fought to be.