Today’s computers contain millions of transistors placed in a tiny piece of sili- 162 con, some so tiny that they can fit in an ant’s mouth. The transistors (devices that control the flow of electric current) are packed and interconnected in layers beneath the surface of the chip, which is used to make electrical connections to other devices. There is a grid of thin metallic wires on the surface of the chip.
This silicon chip was independently co-invented by two American electrical engineers, Jack Kilby and Robert Noyce, in 1958–1959. The chip, along with the invention of the microprocessor, allowed computers to get smaller and more efficient. Silicon chips are also used in calculators, microwave ovens, automobile radios, and video cassette recorders (VCRs).
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.
There is no way specific way to place an order for a baby brother or a baby sister. The gender (boy or girl) of a baby is determined by whether the father’s fertilizing sperm has an X or a Y chromosome. An X chromosome will lead to a girl, and a Y to a boy. (Mothers always contribute an X chromosome.) Although scientific methods are available to help parents organize their chromosomes and take advantage of the fact that the “boy” sperm has less DNA than “girl” sperm, they can be expensive and unreliable. One method, called the Shettles method, recommends that if parents want a girl, they should plan to make a baby right around the time of ovulation.
At this time, the egg is as far away as possible from the incoming sperm so the long-distance runners of the sperm world, the X sperm, have a better chance of making it to the egg. For a boy, the method suggests that parents plan to make a baby about two to four days after ovulation. That way, the short-distance sprinting Y sperm can make it to the egg first. Many doctors say that although this method is based in science, it is no guarantee that a couple will have a baby boy or a baby girl.
James Spangler, a janitor at an Ohio department store who suffered from asthma, invented his “electric suction-sweeper,” in 1907 as way of picking up the dust and debris that triggered his health condition. His invention was the first practical domestic vacuum cleaner. It used an electric fan to generate suction, rotating brushes to loosen dirt, a pillowcase for a filter, and a broomstick for a handle.
Because it was heavy and hard to handle, Spangler sold the rights of his invention to his relative, William Hoover, whose redesign of the appliance coincided with the development of the small, high-speed universal motor, in which the same current (either AC or DC) passes through the appliance’s rotor and stator. This gave the vacuum cleaner more horsepower, higher airflow and suction, better engine cooling, and more portability than was possible with the larger, heavier induction motor. Hoover’s model has since been refined, but the mechanics of his vacuum cleaner are still used in vacuum cleaners today.
Living creatures need oxygen to survive, and fish are no exception. Human beings 68 use their lungs to take in oxygen, and fish breathe using their gills. A fish’s gills are full of blood vessels that absorb the tiny particles of oxygen from the water.
The fish sucks the water in through its mouth and squirts it out through its gills; during this process, the gills take the oxygen from the water into the blood vessels. A fish’s gills are not constructed to take oxygen from the air, so they cannot breathe on dry land.
At least two ancient Greek athletes would have done well in the modern games; their Olympic records stood until the twentieth century. Twenty-six hundred years ago, an athlete named Protiselaus threw a cumbersome primitive discus 152 feet from a standing position. No one exceeded that distance until Clarence Houser, an American, threw the discus 155 feet in 1928. In 656 BC, a Greek Olympian named Chionis leapt 23 feet, 1.5 inches, a long jump record that stood until 1900, When an American named Alvis Kraenzlein surpassed it by 4.5 inches.
Cotton, which comes from flowering Gossypium plants, is a key vegetable fiber used for making clothes, and oil from its seeds can be used in cooking or for making soap. The cotton plant grows in 17 states that make up the U.S. “Cotton Belt”: California, Arizona, New Mexico, Texas, Oklahoma, Arkansas, Missouri, Mississippi, Alabama, Louisiana, Florida, Tennessee, North Carolina, South Carolina, Virginia, Georgia, and Kansas. In the United States, where cotton is no longer picked by hand, machines called pickers or strippers harvest the crops.
Cotton-picking machines have spindles that pick (twist) the seed cotton from the burrs that are attached to plants’ stems. Doffers— a series of circular rubber pads—then remove the seed cotton from the spindles and knock the seed cotton into a conveying system. Conventional cotton stripping machines use rollers equipped with alternating bats and brushes to knock the fluffy white bolls, which contain seeds and hairs, from the plants into a conveyor. After harvest, most of the cotton is pressed into large blocks for storage. These cotton bundles are then transported to the cotton gin, a machine that pulls out the seeds from the cotton bolls.
Skin color—which ranges from light pink to dark brown—is determined by the amount and type of the pigment melanin there is in the skin. Melanin comes in two types: phaeomelanin (red to yellow) and eumelanin (dark brown to black).
Both amount and type are determined by four to six genes. One copy of each of those genes is inherited from your father and one from your mother. Each gene comes in several coding sequences, which results in a variety of skin colors around the world.
Tropical coral reefs are ridgelike or moundlike structures composed of corals and other aquatic organisms. They border the shorelines of more than 100 countries. Although coral reefs comprise less than 0.5 percent of the ocean floor, it is estimated that more than 90 percent of marine species are directly or indirectly dependent on them—they are home to approximately 4,000 species of fish alone.
Reefs protect human populations along coastlines from wave and storm damage by serving as buffers between oceans and near-shore communities. The Great Barrier Reef, located in northeast Australia’s Coral Sea, measures 1,616 miles (2,000 kilometers) in length. It the largest living structure on Earth, and can be seen from the Moon.
Our muscles, which make up about half of our body mass, control the way the body moves. Muscles work together all the time, whether we are actively playing sports, or quietly reading and writing. Muscles lie in bands just beneath the surface of the skin. A muscle is made up of thousands of fibers bundled together within a protective sheath that consists of blood vessels and nerves. These nerves can be up to 12 inches (30 centimeters) long. A muscle becomes stronger when you work it, which is why people Who regularly exercise have more defined muscle tone than those Who do not exercise. There are about 660 muscles in the human body. The three types of muscle tissue are skeletal, cardiac, and smooth. The main and most unique characteristic of muscle tissue is its ability to contract, or shorten, making some type of movement possible.
Skeletal muscles hold the bones together, and are often called “voluntary” muscles because the brain controls them. The cardiac muscle, which is found only in the heart, contracts to send blood from the heart into the arteries. The brain sends signals to the cardiac muscle to speed up or slow down its contractions, called the heartbeat. Smooth muscles, located in the internal organs such as the stomach and intestines, help these organs or tissues do their job, such as help you digest and eliminate your food.