According to the Big Crunch theory, at some point all matter will reverse direction and crunch back into the single point from which it began. Another theory, called the Plateau theory, says that the expansion of the universe will slow to the point where it will nearly cease, at which time the universe will reach a plateau and remain essentially the same.
The Soviet satellite Sputnik 1, which was launched into space on October 4, 1957, was the first spacecraft to go into orbit around Earth. It had no crew members or animals aboard, but instead contained machines that sent information back to Earth via radio.
The former Soviet Union’s (now Russia) launch of Sputnik prompted the United States to get its first satellite, Explorer 1, into orbit quickly, igniting the so-called space race. This was the two countries’ rivalry over being the “first” in many areas of space exploration. Explorer 1’s test run in December 1957 burned on the ground, but the satellite was successfully launched into orbit around Earth on January 31, 1958.
In the Middle Ages, Christmas banquets started at three in the afternoon, with appetizers and fortified mulled wine followed by ten main courses, and lasted until midnight. Today, over the holidays, North Americans consume 24 million turkeys and 112 million cans of cranberries.
We drink 108 million quarts of eggnog and 89 million gallons of liquor. The average weight gain over the Christmas holidays is four to six pounds.
As a matter of fact, yes! Researchers believe that regular contact with pets can reduce levels of stress and reduce blood pressure (the force of blood pushing against the walls of the arteries as the heart pumps out blood).
Pets offer stability, comfort, security, affection, and intimacy. Owning a dog also provides a great opportunity to get exercise and fresh air, since it will need to go for a walk every day.
A bicycle is a simple device that increases the power that you have in the muscles of your legs, taking you faster and farther than you could ever run. When you push the pedals of your bike around once, the pedal sprocket—the wheel with teeth to which the pedals are attached—goes around once, too. But it pulls a chain along, one that is connected to a much smaller sprocket (with fewer teeth to grip each link of the chain) in the center of your bike’s rear wheel. This smaller sprocket moves around a number of times for each single turn of your pedals, moving your bike wheels a lot faster than you’re moving your feet! Some bicycles have several “speeds,” which means that they have a number of gears (called derailleurs) that vary the rate at which the wheels turn. These extra sprockets are located at the pedals and rear wheel of a bike, where levers move the driving chain sideways, from one to another.
A special spring system keeps the chain tight when it changes from a larger to a smaller sprocket. Although you might think that a rider would always want the wheels of his or her bike to move as fast as possible for each pedal turn, that is not always the case. When going uphill, for instance, a rider can get more force out of a wheel that turns fewer times, making the task easier.
A popular summer-camp rhyme is “Leaves of three, let it be.” Poison ivy, the threeleaved plant that grows wild in all regions of the United States, is aggravating to the skin, though not lethal if swallowed unless you are very allergic. After brushing up against the poison ivy plant, a red rash usually develops.
Rubbing the rash will not spread poison ivy to other parts of the body (or to another person) unless urushiol oil—the sticky, resin-like substance that causes the rash—has been left on your hands. Other plants that usually irritate the skin upon contact include cowhage, poison oak, poison sumac, rengas tree, and trumpet vine.
The name “rain forest” comes from the fact that these lush areas of land receive a lot of rain—between 160 and 400 inches per year. They are located near the equator, Which means that their climate is warm. Rain forests cover only a small part of Earth’s surface, about 6 percent, yet they are home to over half the species of plants and animals in the world. For example, the jungles and mangrove swamps of Central America contain many plants and animals found nowhere else, including many types of parrots. The Amazon jungle in South America is the world’s largest tropical rain forest, and is home to one-fifth of the world’s plants and animals.
The forest covers the basin of the Amazon, the world’s second longest river. Central Africa has the world’s second largest rain forest. To the southeast, the large island of Madagascar is home to many unique animals. The rain forests of Asia stretch from India and Burma in the west to Malaysia and the islands of Java and Borneo in the east. Bangladesh has the largest area of mangrove forests in the world. Australia, too, has rain forests: undergrowth in this county’s tropical forests is dense and lush.
Measures refractive indices
Crocodilians—scaly, carnivorous reptiles that include crocodiles, alligators, caimans, and gharials—are descendents of the archosaurs who lived on Earth with the dinosaurs 200 years ago.
Today’s modern crocodiles are semi-aquatic predators that have remained relatively unchanged since the Triassic period. Besides birds, they are the dinosaurs’ closest living relatives.
Before portable cellular phones, people like police officers or taxi drivers communicated from their cars using two-way radios. All of the radios in one city transmitted signals via a large, central antenna located on top of a tall building. With all callers sharing one antenna, the number of calls that could be made at any one time was very limited.
Consumers, like you and me, had an old type of cell phone that was permanently attached to the car and powered by its battery. The first transportable cellular phones had their own battery packs that allowed owners to detach them from the car and carry them in a pouch. However, most weighed about 5 pounds (2.25 kilograms) and were not very practical when used this way.