There are three different ways to pronounce the ‘ED’ ending of regular verbs in the simple past tense: / t/ , / d / or / id /. The pronunciation depends on the sound at the end of the infinitive of the main verb and whether it is voiced or not. A voiced sound is one that vibrates in your throat when you say it.
A deafening boom roars through Pompeii’s crowded marketplace. The ground shakes violently, throwing midday shoppers off balance and toppling stands of fish and meat. People scream and point toward Mount Vesuvius, a massivevolcanothat rises above them.
Nearly 2,000 years ago, Pompeii was a bustling (busy) city located in what is now southernItaly.
But in the summer of A.D. 79, the nearby Mount Vesuvius volcano erupted. It spewed smoke and toxic gas 20 miles into the air, which soon spread to the town. Almost overnight, Pompeii—and many of its 10,000 residents—vanished under a blanket of ash.
Pompeii was basically lost and forgotten until it was rediscovered in 1748. Thanks to excavations, which are still going on today, scientists have been able to figure out almost exactly what happened on that terrible day.
THE SKY IS FALLING
After the volcano first erupted shortly after noon, the thick ash turned everything black—people couldn’t even see the sun. Some residents escaped the city, while others took shelter in their homes. But the ash kept falling. Piles grew as deep as nine feet (3 meters) in some places, blocking doorways and caving in roofs.
Around midnight, the first of four searing-hot (300 degrees Celsius) clouds of ash, rock, and toxic gas (also called surges) rushed down the volcano. Traveling toward Pompeii at about 180 miles an hour (290 km/h), the surge scorched everything in its path. Around 7 a.m., nearly 19 hours after the initial eruption, the city was completely covered in a deadly mix of ash and rock.
LOST AND FOUND
Visiting the ruins of Pompeii is like going back in time. The layers of ash actually helped preserve buildings, artwork, and even the forms of bodies as they decomposed and left holes in the ash. All that allowed experts to fill in the details that might not have survived at many other Roman sites.
Based on what they uncovered, scientists believe that Pompeii was a prosperous town popular with wealthy vacationing Romans. Well-paved streets had high sidewalks and stepping-stones to keep pedestrians out of the mud. To relax, people soaked in public baths, watched gladiators or chariot races at an amphitheater, and enjoyed plays in two theaters.
Pompeii may be ancient history, but scientists are pretty sure Mount Vesuvius is overdue for another major explosion. Luckily the people living near the volcano today will likely receive evacuation warnings before it blows.
Humans have thought about flying for a long, long time. For example, there is the Greek myth of Icarus from 3,000 years ago. (A myth is an old story, often with gods and magic. )
In the Greek myth, Daedalus made wings from feathers held together with wax for himself and his son so that they could escape from an island. He flew successfully from the island of Crete to the city of Naples, but Icarus tried to fly too high and flew too near to the sun, even though Daedalus told him not to fly towards the sun. The wings of wax melted and Icarus fell to his death in the ocean.
In another Greek myth, Bellerophon the Valiant, son of the King of Corinth, captured Pegasus, a winged horse. Pegasus flew him to a battle with the three-headed monster, Chimera.
Pegasus is shown on a Greek vase from around 500 BC. (Museum of Fine Arts, Boston)
Early Research into Flight
The story of the invention of the airplane begins in the 16th, 17th, and 18th centuries, with the first serious research into aerodynamics. Aerodynamics is the way objects move through air (for instance, a wing when it is immersed in a stream of air).
Some of Leonardo's drawings of a "flying machine"
Leonardo da Vinci made the first real studies of flight in the 1480s. He had over 200 drawings and sketches that illustrated his theories on flight. His flying machine was an aircraft that would fly by flapping its wings, a design he created to show how humans could fly. However, he never built this. Leonardo was clearly inspired by the flight of winged animals. In his notes, he mentions bats, kites, and birds as sources of inspiration.
The San Diego Air and Space Museum’s display is a model of one of Leonardo da Vinci’s designs based on his drawings.
Others, such as Galileo Galilei (died 1642) in Italy, Christiaan Huygens in the Netherlands, and Isaac Newton (died 1727) in England worked to understand the movement of air and liquids across surfaces.
Kites
The invention of the kite that could fly in the air by the Chinese started humans thinking about flying. Starting around 400 BC, kites were used by the Chinese in religious ceremonies. They built many colorful kites for fun, also. More sophisticated kites were used to test weather conditions. Kites have been important to the invention of flight as they were the forerunner to balloons and gliders.
The First Hot Air Balloons
The brothers Joseph Michel and Jacques Etienne Montgolfier, who lived in France, were inventors of the first hot air balloon. They used the smoke from a fire to blow hot air into a silk bag. The silk bag was attached to a basket. The hot air then rose and allowed the balloon to be lighter-than-air.
In 1783, the first passengers in the colorful balloon were a sheep, rooster and duck. It climbed to a height of about 6,000 feet (1828.8 meters) and traveled more than 1 mile (1.6 km).
After this first success, the brothers began to send men up in balloons. The first manned flight was on November 21, 1783. The passengers were Jean-François Pilatre de Rozier and François Laurent.
The first free ascent (no rope to the ground) of a hot-air balloon with human passengers, on Nov. 21, 1783. — Jean-François Pilâtre de Rozier and the Marquis d´Arlandes (François Laurent) (Image credit: 2001 National Air and Space Museum, Smithsonian Institution)
Hot air balloons today
Understanding Flight
In the 19th century, mathematicians, engineers and inventors tried to understand the science of flight.
German engineer Otto Lilienthal studied aerodynamics and worked to design a glider that would fly. He was the first person to design a glider that could fly a person and was able to fly long distances. He was fascinated by the idea of flight. Based on his studies of birds and how they fly, he wrote a book on aerodynamics that was published in 1889 and this text was used by the Wright Brothers as the basis for their designs. After more than 2,500 flights, he was killed when he lost control because of a sudden strong wind and crashed into the ground.
German aviation pioneer Otto Lilienthal piloting one of his gliders, around 1895. It did not have an engine, so it was not an airplane.
The videos below shows some of the earliest airplanes from about 1900 to 1920 that did not work.
Planes that did not work
Here are some early attempts at making flying machines.
Finally! The Airplane!
Finally, in 1903, in the United States of America, an airplane flew! The Wright Flyer (also known as the Kitty Hawk,Flyer I or the 1903 Flyer) made the first sustained flight by a manned heavier-than-air powered and controlled aircraft—an airplane—on December 17, 1903. Invented and flown by brothers Orville and Wilbur Wright, it marked the beginning of the pioneer era of aviation.
The first Wright Flyer traveled one hundred twenty feet (36.6 meters) in twelve seconds. The two brothers took turns flying that day with the fourth and last flight covering 850 feet (259 meters) in 59 seconds. But the Flyer was unstable and very hard to control.
The brothers worked for two more years perfecting their design. Finally, on October 5, 1905, Wilbur piloted the Flyer III for 39 minutes and about 24 miles (38 km) of circles. He flew the first working airplane until it ran out of gas.
Humankind was now able to fly! During the next century, many new airplanes and engines were developed to help transport people, luggage, cargo, military personnel and weapons. The 20th century's advances were all based on this first flights by the American Wright brothers.
Orville was at the controls of the machine, lying on the lower wing with his hips in the cradle which operated the wing-warping mechanism. Wilbur Wright ran alongside to balance the machine, and just released his hold on the forward upright of the right wing in the photo.
The driest place on Earth is in Antarctica in an area called the Dry Valleys, which have seen no rain for nearly 2 million years. There is absolutely no precipitation(snow or rain) in this region and it makes up a 4,800 square kilometer region of almost no water, ice or snow. Water features include Lake Vida, Lake Vanda, Lake Bonney and the Onyx River.
There is no net gain of water(the amount of water does not increase). The reason why this region receives no precipitation is because of Katabatic winds, winds from the mountains that are so heavy with moisture that gravity pulls those winds down and away from the Valleys.
One feature of interest is Lake Bonney, a saline (salt) lake situated in the Dry Valleys. It is permanently covered with 3 to 5 meters of ice. Scientists have found mummified(dried and frozen) bodies of seals around the lake. Lake Vanda, also in the region, is 3 times saltier than the ocean. Temperatures at the bottom of this lake are as warm as 25 degrees Celsius.
The Dry Valleys are one of the most extreme desert climates anywhere on earth, a cold desert where the mean annual temperature is between -14C and -30C depending on the site -- windier sites are less cold. An area of the world is called a desert if it has little rain or snowfall. Deserts can be hot (like the Sahara)orcold (like the Antarctic).
(Mean annual temperature - The mean is the average of the numbers and is calculated by dividing the sum of the numbers by the total number of numbers. For example: the mean of 5, 10, 15 is the numbers added up (30) and then divided by the number of numbers (3), so the mean is 10.)
Knowing the difference between "mean" and "median" (the middle number in a series of numbers) can be very useful. - Derek)
Bull Pass, above, in the Dry Valleys. The temperature in the ice and snow-free area is little or no different to the adjacent ice-covered regions, the local geography accounts for the absence of ice.
The next driest place in the world measured by the amount of precipitation that falls is the Atacama Desert in Chile and Peru. There are no glaciers that are feeding water to this area; and thus, very little life can survive. Some weather stations in this region have received no rain for years, while another station reports an average of one millimeter per year.
Squids, octopuses, and cuttlefishes are among the few animals in the world that can change the color of their skin very fast. These cephalopods—a group of mollusks (mollusks are animals like octopuses, oysters, and snails) with arms attached to their heads—can change their skin tone (color, darkness and lightness) to match their surroundings, making them nearly invisible, or give themselves a pattern that makes them easily seen.
Camouflage is the way in which some animals are colored and shaped so that they cannot easily be seen in their natural surroundings.
Many thousands of color-changing cells called chromatophores just below the surface of the skin are responsible for these amazing changes. The center of each chromatophore contains an elastic sac full of pigment (color), rather like a tiny balloon, which may be colored black, brown, orange, red or yellow. If you stretched a dye-filled balloon, the color would gather in one spot, stretching out the surface and making the color appear brighter—and this is the same way chromatophores work. Nerves and muscles control whether the sac is expanded or contracted and, when the sac expands, the color is more visible.
Besides chromatophores, some cephalopods also have iridophores and leucophores. Iridophores have stacks of reflecting plates that create iridescent (shiny like metal) greens, blues, silvers and golds, while leucophores mirror back the colors of the environment (what is around the animal - rocks, sand, etc.), making the animal less conspicuous (less easily seen).
The most obvious reason such a soft-bodied animal (an animal without bones) would change color is to hide from predators (animals that will eat it)—and octopuses are very good at this. They can change not only their coloring, but also the texture of their skin to match rocks, corals and other items nearby. They do this by controlling the size of projections (bumps) on their skin, creating textures ranging from small bumps to tall spikes. The result is a disguise that makes them nearly invisible.
An camouflaged octopus becomes visible suddenly and squirts ink as it swims quickly away
Color changing is just one of an octopus’s defenses, however; it can also spray ink (watch the video above), and make a quick escape through any hole it can get its hidden bony beak through (octopuses have beaks like birds such as parrots).
Intelligence is another way an octopus can defend itself. We'll look at how smart octopuses are in another blog post. This short video will give you an idea of how smart they are. - Derek
Mollusks or Molluscs are a group of soft-bodied invertebrates distributed across ocean, freshwater, and land habitats.
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