Cellular, or cell, phones first became available to consumers in the early 1980s, but the technology that made them small and truly portable evolved gradually over the next 10 years or so. By the beginning of the twenty-first century, millions and millions of people in countries all over the world were using cell phones on a daily basis. And it isn’t just adults who enjoy the benefits of completely mobile phone capabilities: in the United States alone, more than 20 percent of teenagers have a cell phone. That translates to at least one in five American teens. The cellular system divides each city into many small cells (a large city can have hundreds). Each cell has its own tower (which contains an antenna as well as transmitters and receivers that send and receive signals). Each tower can handle numerous callers at a given time, and their small size and weaker signal (compared to the radio antennae) means that their signals don’t interfere with those of nearby towers. When you call someone using a cellular phone, your phone is sending and receiving signals via radio waves, invisible bands of energy that work like light rays. In other words, your cell phone is a fancy, high-tech radio. After you dial a friend’s number, your phone must find the closest tower by searching for the strongest signal. Once that signal is located, your phone transmits certain information—like your cell phone number and serial number—that help your service provider make sure you are one of their customers.
Then the mobile telephone switching office (MTSO) finds an available channel where your conversation can take place. The MTSO then completes the connection (all of this happening in a few short seconds) and you are chatting with your friend, without wires or cords to hold you down. If you are sitting in the back seat of the car while talking, and your mom is driving you from one end of town to the other, your call will be switched automatically from one cell tower to the next without any pause in your conversation.
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.
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.
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.
The suggestion that storks delivered babies came from Scandinavia and was promoted by the writings of Hans Christian Andersen. Storks had a habit of nesting on warm chimneys and would often lift articles from clotheslines then stuff them into these nests, which to children looked like they were stuffing babies down the flue.
The stork is also very nurturing and protective of its young, which helped it become symbolic of good parenthood.
When the time came to honour the patron saint of Ireland’s birthday, church officials gathered solemnly to choose a day, then realized that most of St. Patrick’s life was a mystery. They finally narrowed his birthdate down to either March 8 or 9, but because they couldn’t agree which was correct, they decided to add the two together and declared March 17 to be St. Patrick’s Day.
A virus is a malicious software program that infects computer files or hard disk drives and then makes copies of itself. Many activities that kids do online can leave computers vulnerable to viruses. E-mail attachments are a common means of distributing viruses, but viruses can also be downloaded when you share files and open instant message attachments. In order to keep your computer safe, never open an e-mail attachment you haven’t requested.
Send an e-mail to friends to confirm that they meant to send you an attachment. Also, you can configure your instant messaging program so you can’t receive files from other users. Never download any program without checking with a parent first. You can protect your computer by always running up-to-date firewall software, by running antivirus software regularly, and by periodically scanning your computer for spyware or other unwanted software and immediately removing it.