NASA’s space shuttle, also called the Space Transportation System (STS), takes off from Earth like a rocket but lands like an aircraft. It cannot fly to the Moon, but is used to orbit Earth, where the crew can do scientific work, place satellites in orbit, and visit orbiting space stations. Usually five to seven crew members ride the space shuttles, which have all been launched from Kennedy Space Center in Florida. Six shuttles have been built: the first orbiter, Enterprise, was built in 1974 for testing purposes. Five others have gone into space: Columbia, Challenger, Discovery, Atlantis, and Endeavour.
The space shuttle Challenger disintegrated 73 seconds after launch in 1986, and Endeavour was built as a replacement. Columbia broke apart during re-entry in 2003. NASA announced that the space shuttle would no longer be used after 2010, and from 2014 on would be replaced by the Orion, a new space vehicle that is designed to take humans to the Moon and beyond.
Frogs are able to make their croaking noises because they have simple vocal cords that have two slits in the bottom of the mouth. These slits open into what is called a vocal pouch. When air passes from the lungs through the vocal cords, a sound is produced. The inflating and deflating vocal pouch makes the sound louder or quieter.
That sound changes depending on the kind of frog there are as many different kinds of croaks as there are frogs! Frogs croak for the same reasons that many animals make noises: to track down and then select a mate, and to protect their territory from other male frogs.
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.
Guglielmo Marconi, of Bologna, Italy, was the first to prove that radio signals could be sent over long distances. Radio is the radiation and detection of signals spread through space as electromagnetic waves to convey information.
It was first called wireless telegraphy because it duplicated the effect of telegraphy without using wires. On December 21, 1901, Marconi successfully sent Morse code signals from Newfoundland to England.
Farmers and state governments use chemical pesticides to protect their crops from insect pests, weeds, and fungal diseases while they are growing. They also spray their crops with pesticides to prevent rats, mice, and insects from contaminating foods while they are being stored.
While these actions are meant to benefit human health and bring a wide variety of fruits and vegetables to the supermarket, they can also harm people, wildlife, and the environment. This is why there are strict controls in place over their sale and use.
Most people think that Mercury is the hottest planet because it is nearest to the Sun. However, Venus, the second nearest planet, is the hottest because it has an atmosphere. Its atmosphere is primarily composed of carbon dioxide, which acts like a greenhouse.
The solar heat enters Venus’s atmosphere, but it cannot leave, heating the planet’s surface to about 900 degrees Fahrenheit (482 degrees Celsius). This temperature is hot enough to melt several metals, including lead, tin, and zinc.
About one-tenth of Earth’s surface is always under the cover of ice. And almost 90 percent of that ice is found in the continent of Antarctica. The remaining 10 percent is found on the mountains in the form of glaciers.
The ice sheet that covers Antarctica is almost one-and-a-half times the size of the United States.
Quickly gobbling up cold ice cream may result in “brain freeze,” also know as an ice cream headache. When the cold object touches the roof of your mouth, the blood vessels contract in order to prevent loss of body heat. As the coldness stops, the blood vessels relax again, quickly increasing blood flow to the brain.
This sudden release is What causes the intense headache sensation. You can relieve brain freeze by quickly warming the roof of your mouth: Touch your tongue to the top of your mouth or, if you can roll your tongue in a ball, press the underside of your tongue (which is warmer) to the roof of your mouth. Slowly sipping room-temperature water or pressing a warm thumb against the roof of the mouth also works for some people.
Yes. Not all plants are seed plants. Some plants, such as ferns and mosses, reproduce with spores instead of seeds. Spores, like seeds, can survive harsh conditions and develop into new plants. However, unlike seeds, spores are produced without fertilization and contain neither a plant embryo nor endosperm. Some plants can reproduce without spores or seeds through vegetative reproduction, in which a part of the stem or root gives rise to a new plant.
Scientists often compare Earth to an onion because the planet is made up of many layers of rocks of different densities. On the outside, there is a think crust of hard, cold rock, which is about 4 miles (7 kilometers) thick under the oceans and 22 miles (35 kilometers) thick under the continents. The crust—the layer we live on—surrounds a hard, rocky surface that marks the top of the mantle, called the lithosphere. Most of Earth is made of its mantle, Which goes almost halfway down to Earth’s center.
At the very center is Earth’s core, which has a center of solid iron and nickel about the size of the Moon (called the inner core) and a molten exterior (called the outer core). The temperature of Earth increases about 36 degrees Fahrenheit (2.2 degrees Celsius) for every 0.62 miles (1 kilometer) down you go, reaching temperatures as high as 11,000 degrees Fahrenheit (6,093 degrees Celsius) at its center.