A roller coaster works the same way as a bicycle coasting down a hill. When you ride your bike to the top of a hill, you pedal to get there. Then, to coast down the hill, you take your feet off the pedals and glide down the other side. If the slope is steep enough, you can go very fast. Similarly, a roller coaster is only powered at the beginning of the ride, when the coaster, or train, is pulled up the first hill. When it goes over the top of the hill, the weight of the train itself, pulled downward by gravity, is what keeps the entire unit moving.
There are no cables that pull the train around the track. This conversion of potential energy (stored energy) to kinetic energy (the energy of motion) is What drives the roller coaster, which often reaches 60 miles (96.5 kilometers) per hour. Running wheels guide the train on the track, and friction wheels control the train’s movement to either side of the track. A final set of wheels keeps the train on the track even if it is upside down. Air brakes stop the car as the ride ends.
Just as the tiny fertilized egg cell from which you began divided again and again to become a baby, the trillions of cells now making up your body continue to divide as you grow. The more cells you have, the bigger you become. Some cells divide to replace worn out cells and others divide to increase the size and change the shape of your body as you mature. Hormones—chemicals that are produced by glands and circulate in your blood—help direct the growth of cells in your body during the process of growing up.
Usually people are fully grown by the time they reach the age of 20. By the time a person is 30, however, the rate at which body cells renew themselves begins to slow down, and signs of aging appear. As time goes on, certain body cells—like those of the brain and nerves—are not replaced when they wear out and die.
For about six hundred years, from 1250 to 1850, most parts of the world experienced colder and harsher climates than usual. The cooler temperatures were caused by a combination of less solar activity and large volcanic eruptions. Northern Europe’s Little Ice Age took place between 1430 and 1850. When the climate became colder, crops died, and there was widespread famine and disease.
Although it was not a true ice age because it did not get cold enough for long enough to cause ice sheets to grow larger, England experienced some of the coldest winters in its history during the 1820s. Its longest river, the River Thames, froze over regularly and townspeople held Frost Fairs, during which they played games and danced on its icy surface.
The mayor-council is the oldest form of city government in the United States. Its structure is similar to that of the state and national governments, with an elected mayor as chief of the executive branch and an elected council that represents the various neighborhoods, forming the legislative branch. The mayor appoints heads of city departments and other officials.
The mayor also has the power to veto the laws of the city (called ordinances), and prepares the city’s budget. The council passes city laws, sets the tax rate on property, and decides how the city departments spend their money to make the city a better place.
The custom of a “honeymoon” began over four thousand years ago in Babylon, when for a full lunar month after the wedding, the bride’s father would supply his son-in-law with all the honey-beer he could drink. It was called the “honey month.”
The word honeymoon didn’t enter our language until 1546, and because few people could afford a vacation, a honeymoon didn’t mean a trip away from home until the middle of the nineteenth century.
In the nineteenth century, Samuel A. Maverick was a stubborn Texas rancher who, because he said it was cruel, refused to brand his cattle even though it was the only way to identify who owned free-range livestock.
Instead he would round up all the unbranded cattle he could find, even those not from his own herd. At first any stray unbranded cow was called a “maverick,” but the word has grown to mean anyone Who doesn’t play by the rules.
In the Arctic and Antarctic circles there is at least one day a year when the Sun does not rise and one day when the Sun does not set. This is because of their close location to Earth’s poles.
The Sun does not set on the summer solstice (June 21 in the north and December 21 in the south) and does not rise on the winter solstice (December 21 for the north and June 21 for the south). For this reason, the Arctic and Antarctic are called the “lands of midnight Sun” in the summer and “lands of noon darkness” 12 in the winter.
Kissing bridges are covered bridges with roofs and wooden sides. They are called kissing bridges because people inside the bridge cannot be seen from the outside, making them good places to kiss discreetly. They were first built in the nineteenth century by engineers who designed coverings to protect the structures from the effects of the weather.
More than 10,000 covered bridges were built across the United States between 1805 and the early twentieth century. As of January 1980, only 893 of these covered bridges remained—231 in Pennsylvania alone, where the first one was erected.
The Internet is an amazing place where you can find information on all kinds of things. You can chat with friends, e-mail long-distance pen pals, and read what other people are saying about things you are interested in. But just as you should not talk to strangers when you are in the outside world, you should also use caution when chatting in the cyber world. Unfortunately, there are people surfing the Web who present a threat to kids.
They may be adults posing as another kid or somehow lying to you about who they are and what they want. To be safe, never give anyone you don’t know personal information about yourself online—including your name, address, phone number, or e-mail password. And never agree to meet a person you’ve chatted with online, even if that person seems friendly or harmless. Let your parents know if a stranger is sending you e-mail or instant messages.
As a system of voting, the ancient Greeks placed beans in a jar. They called these small beans or balls “ballota,” which gives us the word ballot. A white bean was a “yes” and a brown bean was a “no.”
The beans were then counted in secret so the candidates wouldn’t know who voted for or against them. If the container was knocked over, and the beans were spilled, the secret was out of the jar.