The triangular shape of a tricycle, with its three wheels spread apart, is much more stable than a regular bicycle, which balances on two aligned wheels. (The “tri” [three] and “bi” [two] before “cycle” refers to the number of wheels each vehicle has.) Tricycles suit young children well; with larger heads and undeveloped muscles, little ones lack the coordination and balance needed to ride regular bikes. But as soon as they can learn to pedal, children can ride a tricycle, turning leg power into wheel power.
A tricycle is built for stability and not for speed: its pedals are attached to a sprocket in the center of its large front wheel, which moves around once for each completed pedal turn. So the larger the front wheel of a tricycle, the faster it will go—but it cannot be so large that young legs cannot reach the pedals! This design makes a tricycle unlike a regular bike, which has chain-driven sprockets that move its wheels a lot faster than its rider’s feet. Tricycles are also easier for little ones to steer and turn because they are pulled forward by the movement of their front wheels; regular bikes are powered by their rear wheels.
Butterflies and other insects fly from one plant to the next to feed on the sweet nectar— and sometimes the pollen—located in the interior of flowers. The sugar in nectar supplies insects with the energy they need, and pollen contains protein, fat, vitamins, and minerals. In the process of feeding, many insects transfer pollen—which sticks to their bodies—from one plant’s flower to another.
Pollen, which is a fine powdery grain from a flower’s male reproductive organ, must be transferred to the female reproductive organ of a flower for fertilization to take place and seeds to form.
Husbands and wives divorce when they can no longer live happily together. It is usually a sad thing, because when people marry they expect to be with their partner for the rest of their lives. But over the course of a marriage things happen, people can change, and the happiness that the couple was so sure of in the beginning sometimes disappears. When couples with children get divorced it is even more unfortunate because more people are affected. Many children feel bad when their parents divorce because their family will not be the same. After a divorce, they generally do not see one of their parents as much as they did before.
Still, just because the feelings between a mother and a father change doesn’t mean that their love for their children changes in any way. It’s important to remember that divorce is something that happens between a husband and wife—it has nothing to do with the kids. Many children feel that if they adjust their behavior somehow their parents will want to stay together, but divorces are not caused by anything children do.
According to the National Aeronautics and Space Administration (NASA), Which is in charge of space exploration and scientific discovery for the United States, the Hubble transmits about 120 gigabytes of science data every week. That’s equal to about 3,600 feet (1,097 meters) of books on a shelf. The growing collection of pictures and data is stored on magneto-optical disks. Among its many discoveries, Hubble has revealed the age of the universe to be about 13 to 14 billion years, which is a more accurate estimate than the Big Bang range of between 10 to 20 billion years.
Hubble also played a key role in the discovery of dark energy, a mysterious force that causes the expansion of the universe to accelerate. Hubble has shown scientists galaxies in “toddler” stages of growth, helping them understand how galaxies form. It found protoplanetary disks, clumps of gas and dust around young stars that likely function as birthing grounds for new planets. It discovered that gamma-ray bursts—strange, incredibly powerful explosions of energy—occur in far-distant galaxies when massive stars collapse.
As people age, their bodies change in many ways that affect the ways their cells and organ systems function. These changes occur little by little, progress over time, and are different for every man and woman. We all lose height as we age, and by the time we reach 80 years old, our height may have decreased by two inches (five centimeters). Changes in posture, in the growth of our spine’s vertebrae, and joint changes all contribute to our loss of height. With aging, the hair follicles produce less melanin, the pigment that gives hair its color.
Hair becomes lighter, gray, and eventually turns white. The nails also change with aging: they grow slower, may become dull and brittle, and may become yellowed and opaque. With aging, the outer skin layer (epidermis) thins and the number of pigment-containing cells (called melanocytes) decreases, but the remaining melanocytes increase in size. Aging skin thus appears thinner, more pale, and translucent. Changes in the connective tissue reduce the skin’s strength and elasticity, resulting in a wrinkly, leathery skin.
Pin money became an English phrase to describe extra cash set aside by wives to run the household at the turn of the twentieth century, When pins were rare enough to be sold on just two days of the year, January 1 and 2.
Although through time pins became more commonplace and far less expensive, the British courts still enforce any prenuptial agreement or property lien demanded by the wife as the “pin money charge.”
Mosses and fungi probably appeared about 400 million years ago. By about 200 million years ago, the earth sprouted sweeping forests of giant cycads, conifer trees, huge horsetails, and ferns. But the first flowering plants did not appear until the dinosaurs, sometime in the middle of the Cretaceous period, about 100 million years ago.
Before this, most of the trees had been gymnosperms, or plants with cones. Magnolias are among the oldest of all flowering plants, appearing about this time, along with orchids. With flowers came many insects, including butterflies, ants, termites, and bees. The flowering plants provided food for these insects, who spread the pollen from flower to flower to produce the seeds that would keep the flowers reproducing.
A fossil is the hardened remains or an imprint of a plant or animal that lived a very long time ago. Some fossils are thousands of years old, others are several hundred million years old. Most plants and animals died and then decayed without ever leaving a trace. But some were buried under mud, rocks, ice, or other heavy coverings before decaying. The pressure of these layers over thousands of years turned animal and plant remains into rock.
Usually fossils preserve the organism’s hard parts: the bones or shells of an animal and the seeds, stems, and leaf veins of plants. Sometimes the fossil is the actual animal part, like a bone or tooth, that has hardened into rock. Some fossils, called trace fossils, show the imprint of parts of the animal or plant. Occasionally these imprints act as a mold, and the sediment that fills the imprint hardens and becomes a cast of, for example, a dinosaur footprint. Sometimes bones or trees are preserved by minerals that seep into the part’s pores and then harden, or petrify, that part. Arizona’s Petrified Forest contains numerous examples of giant trees that were petrified millions of years ago.
The Greeks borrowed celebrating birthdays from the Egyptian pharaohs and the cake idea from the Persians. Then early Christians did away with birthday parties for a while until the custom re-emerged with candles in Germany in the twelfth century.
Awakened with the arrival of a birthday cake topped with lighted candles, which were changed and kept lit until after the family meal, the honoured child would make a wish that, it was said, would come true only if the candles were blown out in a single breath.
The combine harvester saves the farmers time and labor. Before modern machinery, harvesting crops was a painstaking process. Gathering and removing mature plants from the field had to be done by hand. Farm workers used sharp-bladed, long-handled scythes and curved sickles to cut down cereal crops like wheat. Even the fastest reaper could only clear about a third of an acre a day. Because rain could ruin harvested wheat, workers called sheaf-makers quickly tied it into bundles, so that it could be safely stored if the weather turned stormy. During the long winter months farm workers used jointed wooden tools called flails to thresh or beat the dried wheat in order to separate its edible grain seeds from its stalks.
But in 1786 a machine that threshed wheat by rubbing it between rollers was invented, replacing human threshers. And around 1840 a reaping machine—whose revolving wheel pressed grain stalks against a sharp blade that cut them down— replaced human harvesters. Today, farm machines called combine harvesters do this work in much the same way. These machines are very efficient and combine all three jobs of cutting, collecting, and threshing a crop. A single combine harvester can process five acres of wheat in less than an hour!