In 1823, the English mathematician originated the concept of a programmable computer. At this time, he persuaded the British government to finance what he called an “analytical engine.” This would have been a machine that could undertake any kind of calculation. It would have been driven by steam, but the most important innovation was that the entire program of operations was stored on a punched tape (a long strip of paper in which holes are punched to store data).
Babbage’s machine was not completed in his lifetime because the technology available to him was not sufficient to support his design. However, in 1991 a team lead by Doron Swade at London’s Science Museum built the analytical engine (sometimes called a “difference engine”) based on Babbage’s work. Measuring 10 feet (3 meters) wide by 6.5 feet (2 meters) tall, it weighed three tons and could calculate equations down to 31 digits. The feat proved that Babbage was way ahead of his time, even though the device was impractical because one had to a turn a crank hundreds of times in order to generate a single calculation. Modern computers use electrons, which travel at the speed of light.
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.
Although a helicopter doesn’t have wings like an airplane, it uses the same principle of lift to rise and maneuver in the air. The blades of a helicopter’s propeller-like top rotor are shaped just like a plane’s wings—flat on the bottom and rounded on the top—and are likewise adjustable. Instead of rushing forward through the air like a plane does to gather enough lift to fly, a helicopter moves only its (three to six) rotor blades, which are attached to a central shaft driven by an engine.
The rotor blades slice through enough air—creating the changes in surrounding air pressure that produce lift—to achieve flight. Adjusting the angle at which the rotor blades are set helps control a helicopter’s lift and manner of flight. Because the angle of the rotor is adjustable, too, a helicopter has far greater maneuverability than an airplane: besides moving up, down, and forward, it can fly backward and hover in the air.
Television works through a series of complicated processes. It starts with a television camera, which takes pictures of scenes. Photo cells inside the camera change the pictures to electrical signals. At the same time, a microphone records sounds that are occurring during the scenes. A vibrating magnet in the microphone changes these sounds into electrical signals, too. Some television shows, like news reports, are recorded live, which means that they are broadcast to homes as they occur. But most of the television programs that we watch are recorded, which means that they are put on videotape and sent out later. The electrical signals of sound and pictures are stored as magnetic signals on videotape, which are converted back to electrical signals when played. Before a program is broadcast, its electrical picture and sound signals are run through a device called a television transmitter. With the help of strong magnets, the transformer turns the electrical signals into invisible bands of energy called radio waves (similar to visible light waves), which can travel great distances through the air. They can travel directly to outdoor television antennae, which catch the waves and send them to television sets that change them into pictures and sounds again.
Cable companies send electrical picture and sound signals through cables directly to homes. When broadcasting to distant places, communication satellites that orbit Earth are used to bounce or return the waves back to Earth, extending their travel distance. Satellites are necessary because radio waves move in straight lines and cannot bend around the world. When an antenna or satellite dish receives radio waves, it changes them back into electrical signals. A speaker in a television set changes some of the signals back into sound. The pictures are reproduced by special guns at the back of a television set that shoot electron beams at the screen, causing it to glow with tiny dots of different colors. Viewed together, the dots look like a regular picture. The individual pictures that make up a scene are broadcast and received, one after another, at a pace so quick that it looks like continuous action is occurring on the screen. The entire process happens very fast because television stations and broadcast towers are all around and because radio waves travel very quickly, at the speed of light. Radio programs broadcast talk and music across the airwaves using the same technology.
Air is a mixture of gases that circle Earth, kept in place by gravity. Air makes up Earth’s atmosphere. The air we breathe is 78 percent nitrogen gas, 21 percent oxygen, 0.9 percent argon, and 0.03 percent carbon dioxide, along with water vapor (floating molecules of water).
Also present are traces of other gases and tiny bits of dust, pollen grains from plants, and other solid particles. As our atmosphere extends higher and higher above Earth, toward outer space, air becomes thinner and the combination of gases in the air changes.
Scientists believe that the solar system in about 4.6 billion years old. Earth and the rest of the solar system formed from a giant cloud of gas and dust. Gravity and rotational forces caused the cloud to flatten into a disc and much of the cloud’s mass to drift into the center. This material became the Sun. The leftover parts of the cloud formed small bodies called planetesimals.
These planetesimals collided with each other, gradually forming larger and larger bodies, some of which became the planets. This process took approximately 25 million years, according to scientific estimates.
Earth Day is a national holiday that was first celebrated on April 22, 1970. It was created by Senator Gaylord Nelson, a Democrat from Wisconsin who was elected to the U.S. Senate in 1962. Senator Nelson decided to set aside one day aside for the entire nation to focus on environmental issues, learn about ways to improve the environment, and protest against the federal government’s unwillingness to help solve problems such as air pollution and the widespread destruction of forests.
After lots of hard work and publicity, on the first Earth Day 20 million Americans gathered at different places from the East to West coasts to hear speeches, participate in community-wide cleanup efforts, and demonstrate to the government that the environment is a major national issue. Ever since then, April 22 has been the date for celebrating Earth Day—a time when the United States (and now many countries all over the world) could participate in educational activities that celebrate Earth and think of new ways to preserve our natural resources. On Earth Day 2008, over 100 million people joined in the effort to celebrate and protect our planet.
Boats need a power source to move them forward in the water. In small vessels this power can be provided by people, who use oars to paddle along. Muscle power cannot move boats very fast or very far, though. The wind can be used, too, to move boats equipped with sails. But for a large boat that needs to go a long distance, the most reliable source of power is a motor-driven engine. Depending on the size of the boat, a gasoline engine, diesel engine, or steam engine does the job. Nuclear power is even used to run some boat engines, like those found in submarines. Motors rotate boat propellers, which have large twisting blades that radiate around a central hub.
These blades push water backward, and the boat moves forward as the disturbed water pushes back. Rotating propellers also create lower water pressure in the space in front of them, which sucks them forward, along with the vessel to which they are attached. (Using these same principles of movement, propellers can also power aircraft.) A boat is steered by a rudder, Which is a flat, upright, movable piece of wood or metal that is attached to its stern, or rear. When turned, the rudder changes the direction of the water around it, which pushes back, forcing the stern, and gradually the rest of the boat, to change direction, too.
Yes. The air inside your home might be filled with toxins from tobacco smoke, cleaning products, ceiling tiles, and upholstery. Scientists have discovered that many types of houseplants absorb airborne pollutants as part of their normal “breathing” process—they take carbon dioxide in through their leaves, and let oxygen out. The plant transports these toxins to their roots, where microbes feed on and detoxify them.
Although scientists disagree about how many—and what types of—houseplants it takes to clean the air, they suggest using a mix of plants. Bill Wolverton, a former NASA scientist and environmental engineer, studies the effects that plants have on air quality and has rated the areca palm, lady palm, bamboo palm, rubber plant, and dracaena as highly effective at clearing pollutants from the air.
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.