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.
Both bravery and courage are acts of valour and imply a certain strength and fearlessness. There is, however, a subtle difference in meaning between the two words. Courage comes from the French word coeur, meaning heart. It is a quality of character that allows someone to carry through with a difficult premeditated plan of action.
Bravery, on the other hand, comes from the Spanish word bravado, meaning a single or spontaneous act of valour. It is not planned, but rather a kneejerk reaction that often occurs within a crisis.
People can use the Internet to send electronic mail, known as e-mail, to one another in just a few seconds. Once you type a message into your computer to send to your cousin, let’s say, who lives miles from you across the country, it travels through the wires of your phone line as a series of electrical signals (or, for some people, the signals travel through the same cables that bring them cable television). These signals travel to a station run by your service provider, where a big computer sends them to an Internet routing center. Located all over the world, routing centers, which are linked to organizations and Internet providers, send the countless computer communications that come to them each second along the quickest possible routes to their destinations.
A giant computer there reads the address on your e-mail and sends it farther: depending on the distance it must travel, it may continue along phone lines, be changed into light signals that can travel with great speed along thin glass strands called fiber-optic cables, or be converted into equally speedy invisible bands of energy known as radio waves and transmitted to a communications satellite that will bounce it back to Earth, to a ground station located close to where your cousin lives. Once your message reaches the routing center nearest your cousin, it will be sent to the station of his or her service provider. From there it will be sent along regular phone lines to his or her computer. And all of this happens in a matter of moments.
Thousands of years ago there were no numbers to represent one, two, or three. Instead, people used fingers, rocks, sticks, or eyes to represent numbers. There were neither clocks nor calendars to help keep track of time. The Sun and the Moon were used to distinguish between 1:00 P.M. and 4:00 P.M. Most civilizations did not have words for numbers larger than two so they used terminology familiar to them such as flocks of sheep, heaps of grain, piles of sticks or stones, or groups of people. People had little need for a numeric system until they formed clans, villages, and settlements and began a system of bartering and trade that in turn created a demand for currency. The Babylonians, who lived in Mesopotamia, between the Tigris and Euphrates rivers, began a numbering system about 5,000 years ago. It is one of the oldest numbering systems in the world. The ancient Egyptians used special symbols, known as pictographs, to write down numbers more than 3,000 years ago. The Babylonians and the Egyptians were the first to complete a system for arithmetic based on whole numbers and positive rational numbers. About 500 B.C.E. the Romans developed a system of numerals that used letters from their alphabet rather than special symbols (for example, III represented three). Roman Numerals was the standard numbering system and method of arithmetic in ancient Rome and Europe until about 900 C.E., when the Arabic numbering system, which was originated by the Hindus, came into use. Today, we use numbers based on the Hindu-Arabic system. We can write down any number using combinations of up to 10 different symbols (0, 1, 2, 3, 4, 5, 6, 7, 8, and 9).
During the last decade of the nineteenth century, the electric vehicle became especially popular in cities across America. People had grown familiar with electric trolleys and railways, and technology had produced motors and batteries in a wide variety of sizes. The Edison Cell, a nickel-iron battery, became the leader in electric vehicle use. By 1900, electric vehicles were the most popular car. In that year, 4,200 automobiles were sold in the United States. Of these, 38 percent were powered by electricity, 22 percent by gasoline, and 40 percent by steam. By 1911, the automobile starter motor did away with handcranking gasoline cars, and Henry Ford had just begun to mass-produce his Model T’s. By 1924, not a single electric vehicle was exhibited at the National Automobile Show, and the Stanley Steamer was scrapped that year. Because of “Clean Air” legislation, the energy crises of the 1970s, and concern for the well-being of the environment, car manufacturers have again marketed several all-electric cars and “hybrid” vehicles.
Hybrid cars use two or more different power sources to propel them, such as a gasoline engine and an electric motor. General Motors sold the Impact, an electric vehicle. And Honda offered people two hybrids, the Insight and a Civic sedan. The Toyota Prius is a hybrid that first went on sale in Japan in 1997, making it the first mass-produced hybrid vehicle. According to the United States Environmental Protection Agency, the 2008 Prius is the most fuel-efficient car sold in the United States. Because of this, electric cars and hybrid vehicles may be the new cars of the future, eventually replacing all-gasoline-powered cars.
Antarctica is the coldest, highest, windiest, driest, and iciest continent on Earth. Winds can reach up to 200 miles (322 kilometers) per hour for five hours per day!
The expression “putting on the dog,” meaning showing off, comes from the practice leisurely wealthy women had of carrying lapdogs to afternoon social functions. “Dressed to the nines” comes from a time when the seats furthest from the stage cost one pence, and the closest, nine pence. Sitting in the expensive seats required dressing up to fit in with the well-off. It was called “dressing to the nines.”
Yes, the salmon is most famous for its life cycle. It is born in tiny streams far from the sea, where it spends the first part of its life in freshwater. In the springtime, it migrates down streams to rivers, sometimes traveling hundreds of miles, until it ends up in the open ocean, where it spends much of its adult life. Then, when it’s time to lay its eggs, the salmon makes the journey back to its birthplace to spawn and die. The salmon’s body is rich in oils that are picked up during its life in the ocean. The oil helps give the salmon the energy it needs to navigate the journey upriver.
The coco de mer tree, a palm that only grows today on two islands in the Seychelles, produces both the largest seed (each weighs about 44 pounds [20 kilograms]) and the largest nut in the world. The nut, which takes six to seven years to mature and another two years to germinate, is sometimes called the sea coconut or Seychelles nut. When early explorers first discovered the nut, they thought it came from a mythical tree at the bottom of the sea.
Sixteenth-century European nobles decorated the nut with jewels as collectibles for their private galleries. Today, the coco de mer is a rare protected species.
When you get sick, part or all of your body is not working as it should. The cause of sickness can come from inside your body or from the outside world. Diseases that start on the inside are usually inherited in the genes that you receive from your parents, Which make up the master plan that determines how your body will grow and run. Abnormal development or functioning of different body systems is the cause of many chronic (long-lasting) diseases. Things in the outside world can cause sickness, too. Poisons in the environment can cause illnesses in people. Not eating the right foods, with their important nutrients, can also cause diseases. But the most common cause of sickness from the outside world is infectious agents. These agents are usually microscopic organisms (living things so small that they can only be seen with the help of microscopes) like bacteria and viruses, which we commonly refer to as germs.
Bacteria and viruses and other microscopic organisms live in the air, water, and soil that make up our world. They are on the things and people we touch and in the food we eat. Many of them are beneficial: bacteria are needed to make cheese, some bacteria help vegetables like peas and beans grow, and some bacteria clean the environment and enrich the soil by feeding on dead plants and animals. But there are other microscopic organisms that invade the bodies of plants and animals—and people—and cause diseases.