An earthquake (also known as a quake, tremor or temblor) is the perceptible shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth's crust that creates seismic waves. Earthquakes can be violent enough to toss people around and destroy whole cities. The seismicity or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time. Earthquakes are measured using observations from seismometers. The moment magnitude is the most common scale on which earthquakes larger than approximately 5 are reported for the entire globe. The more numerous earthquakes smaller than magnitude 5 reported by national seismological observatories are measured mostly on the local magnitude scale, also referred to as the Richter magnitude scale. These two scales are numerically similar over their range of validity. Magnitude 3 or lower earthquakes are mostly imperceptible or weak and magnitude 7 and over potentially cau
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In physics and engineering, for a dynamical system according wave theory, a mode is a standing wave state of excitation, in which all the components of the system will be affected sinusoidally under a specified fixed frequency. Because no real system can perfectly fit under the standing wave framework, the mode concept is taken as a general characterization of specific states of oscillation, thus treating the dynamic system in a linear fashion, in where linear superposition of states can be performed. As classical examples, there are: * In a mechanical dynamical system, a vibrating rope is the most clear example of a mode, in which the rope is the medium, the stress on the rope is the excitation, and the displacement of the rope with respect to its static state is the modal variable. * In an acoustic dynamical systems, a single sound pitch is a mode, in which the air is the medium, the sound pressure in the air is the excitation, and the displacement of the air
The impact of so many humans on the environment takes two major forms: consumption of resources such as land, food, water, air, fossil fuels and minerals. waste products as a result of consumption such as air and water pollutants, toxic materials and greenhouse gases. * The world population is growing by approximately 74 million people per year * Population growth is not evenly distributed across the globe * Scientists are yet to conclusively determine the human ‘carrying capacity’ of Earth * Population is only one of many factors influencing the environment * We have consumed more resources in the last 50 years than the whole of humanity before us * The 20 th century saw the biggest increase in the world’s population in human history. In 2015 the world population is more than 7.3 billion people . That’s more than seven billion three hundred million bodies that need to be fed, clothed, kept warm and ideally, nurtured and educated. More than 7.3
Compare shadows: Advertisement The first person to estimate the circumference of the Earth was a Greek mathematician named Eratosthenes, who was born in 276 B.C. He did so by comparing shadows case on the day of the summer solstice in what is today Aswan, Egypt, with the more northerly city of Alexandria. At noon, when the sun was directly overhead in Aswan, there were no shadows. In Alexandria, a stick set in the ground cast a shadow. Eratosthenes realized that if he knew the angle of the shadow and the distance between the cities, he could calculate the circumference of the globe. On a flat Earth, there wouldn't have been any difference between the length of the shadows at all. The sun's position would be the same, relative to the ground. Only a globe-shaped planet explains why the sun's position should be different in two cities a few hundred miles apart. Go climb a tree: This is another one of those self-evident things: You can see farther if
BRIEF THEORY , REACTION, MECHANISM AND APPLICATION OF Sandmeyer Reaction Reimer Tiemann Reaction Hofmann Bromamide Reaction 1-Sandmeyer Reaction § Sandmeyer reaction affords a useful method for introducing a halogen substituent at the desired position of an aromatic ring . § The method involves the conversion of an aromatic primary amine into an aryl diazonium salt by treatment with nitrous acid in the presence of mineral acid (usually Hydrochloric acid and sulphuric acid ) at low temperature ( 0-5°C ) subsequent decomposition of the diazonium salt by heating with cuprous chloride or bromide in the presence of an excess of the corresponding halogen acid gives aryl chloride or bromide . § The overall reaction is thus the replacement of the amino group of the aromatic amine by halogens. REACTION: MECHANISM: § It seems that cuprous c