The head louse is a tiny, wingless insect that lives in human hairs and feeds on very small amounts of blood drawn from the scalp. Although they may sound kind of disgusting, lice appear often on young children in common settings, such as school. Lice aren’t dangerous and they don’t spread disease, but they are contagious and can be very annoying. Their bites may cause the scalp to become itchy and inflamed, and scratching may lead to skin irritation. They can be hard to get rid of, and take lots of work to make them go away and stay away.
Usually, using special medicated shampoos and thoroughly cleaning sheets, carpets, clothing, and personal products, like combs and brushes, gets rid of the pesky insects. Kids should try to avoid head-to-head contact at school (both in classrooms and on the playground) and while playing at home with other children. They also shouldn’t share combs, brushes, hats, scarves, bandanas, ribbons, barrettes, towels, helmets, or other personal care items with anyone else, whether they may have lice or not.
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.
Robots like ASIMO and Mahru are sophisticated, expensive, highly technologically advanced machines that are built upon major components found in humans. Robot technicians use the inner workings of the human body as the model for the robots that they make. This modeling ensures that their robots are as lifelike as possible. First, the robot technician designs the five major components he or she will put into the robot: a body structure, a muscle system, a sensory environment, a power source, and a brain system.
Next, they build an intricate machine made up of electrical circuits, electrical valves, piston cylinders, electric motors, solenoids, hydraulic systems, and more—each plays a specific role in getting the robot to work. Every robot has a computer that controls everything else within its body. Many robots can talk and some can even smell, taste, and hear. To get the body of a robot moving, the computer must “tell” the specific part to move. If the technician wants the robot to do something new once it has been made, he or she writes a new computer program. In some cases, if the task is too big for the robot’s wiring system, new parts need to be installed. NUMBERS AND COUNTING
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!