The inability to hear, or deafness, can occur for many reasons. Some types of hearing loss result from something blocking sound as it travels from the outer ear to the eardrum and the tiny bones in the middle ear. Other types of loss arise from damage to or a defect of the inner ear or the auditory nerve, which is the nerve that carries sound signals from the inner ear to the brain. Deafness can happen as a result of disease, including severe ear infections, or it can be inherited, with the deafness being apparent at birth or sometimes showing up years later. Injuries and accidents also account for many cases of deafness.
Extremely loud noises, like those that come from an explosion, can cause deafness, though that loss of hearing is sometimes temporary. People who work in noisy factories or those who are frequently exposed to very loud music can also develop hearing loss over time. Many people gradually lose some or all of their hearing when they reach old age, but some of those types of hearing loss can be overcome by wearing a hearing aid, which makes noises like speech or music louder.
You may have heard this expression used in school, in television commercials, or on a sign at your local parks and recreation. Basically, the slogan means that there are three key ways to produce less waste:
1. Reduce the amount of trash (and toxicity) you throw away.
2. Reuse containers and products whenever possible.
3. Recycle as much as possible and buy products with recycled content. As much as 84 percent of all household waste can be recycled—so it makes sense to be conscious of what we use and how we can reuse it.
First built in 1960 by American physicist Theodore Maiman, lasers are machines that produce intense beams of high-energy light. Laser light is more powerful than ordinary light because all its rays have the same wavelength and move together in exactly the same direction, allowing them to be focused in a narrow beam with great precision.
Laser light beams vary in strength, depending on the materials and amount of energy used to make them. Lasers can melt, burn, or cut through a variety of different surfaces, from hard metal to the delicate human body, which is why they are often used in surgery today. Lasers can be used to make precise measurements, to reshape corneas to correct poor vision, to transmit telephone signals, to guide weapons, and to read supermarket bar codes.
On the outside, most electric cars look exactly like gas-powered cars. An electric car does not have a tailpipe or a gas tank, but the overall structure is basically the same. Instead of a huge engine, an electric car uses an electric motor to convert electric energy stored in batteries into mechanical energy.
Different combinations of generating mechanisms—solar panels, generative braking, internal combustion engines driving a generator, fuel cells— and storage mechanisms are used in electric vehicles.
Living species of sequoias are some of the biggest and widest trees in the world. The tallest trees are the coastal redwoods of California, while the widest ones are the giant sequoias, which have much larger trunks and branches. These trees grow in the Sierra Nevada mountains of Central California at elevations of about 6,500 feet (1,981 meters). The trees have survived for 2,000 or 3,000 years. Some of the largest sequoia trees measure 35 feet (10.6 meters) in diameter and up to 300 feet (91 meters) in height.
Their bark can be 4 feet (1.2 meters) thick! Many are found in California’s Sequoia National Park. The General Sherman, for example, is one of the tallest giant sequoias in the world, with a height of about 275 feet (85 meters).
In ancient times, just as today in third-world societies, dogs lived miserable lives with little or no human care, which led to the hard-times expressions, “it’s a dog’s life,” “sick as a dog,” and “dog-tired.” As for the proverb “Every dog has his day,” it was first recorded as an epilogue after the famed Greek playwright Euripides was killed by a pack of dogs in 405 BC.
Scientists estimate that Earth—born out of a swirling cloud of gas and dust—is about 4.6 billion years old. They have reached this conclusion by studying Moon rocks and meteorites (rocks that have fallen from space to Earth) that they believe were formed at the same time as our planet.
The Chinese lunar calendar is based on the cycles of the Moon, and is constructed in a different fashion than the Western solar calendar. In the Chinese calendar, the beginning of the year falls somewhere between late January and early February, and contains 354 days.
Each year is given an animal designation, such as “Year of the Ox.” A total of 12 different animal names are used, and they rotate in the following sequence: Rat, Ox, Tiger, Hare (Rabbit), Dragon, Snake, Horse, Sheep (Goat), Monkey, Rooster, Dog, and Pig. The Chinese have adopted the Western calendar since 1911, but the lunar calendar is still used for festive occasions such as the Chinese New Year. Many Chinese calendars print both the solar dates and the Chinese lunar dates.
Located in Arizona and stretching to Colorado, the Grand Canyon is 18 miles (29 kilometers) wide, 227 miles (365 kilometers) long, and 6,000 feet (1,828 meters) deep in its deepest section. It takes about two days by foot or mule to travel from the top to the bottom.
Although it is not the biggest canyon in the world—Barranca de Cabre in northern Mexico and Hell’s Canyon in Idaho are deeper—it is known for its amazing landscape. The canyon’s walls are made up of rocks, cliffs, hills, and valleys formed millions of years ago, and it is home to hundreds of species of mammals, reptiles, and birds. Although people lived in the canyon some 4,000 years ago, today it is a national park and national landmark.
There is no such thing as “earthquake season.” Earthquakes happen in cold weather, hot weather, dry weather, and rainy weather. Weather, which takes place above Earth’s surface, does not affect the forces several miles beneath the surface, where earthquakes originate.
The changes in air pressure that are related to the weather are very small compared to the forces in Earth’s crust, and the effect of air pressure does not reach beneath the soil.