22 résultats pour "measuring"
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Temperature
I
INTRODUCTION
Thermometers
Mercury and digital thermometers are the most common types of household devices for measuring body temperature.
range of the water, which differs for various species. Thus, for example, the increase in temperature of river water by only a few degrees as a result of heat dischargedfrom power plants may kill most of the native fish. See Water Pollution. The properties of all materials are also markedly affected by temperature changes. At arctic temperatures, for example, steel becomes very brittle and breaks easily,and liquids either solidify or become very viscous, offering high frictional resistance to...
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Quantum Theory
I
INTRODUCTION
Quantum Theory, in physics, description of the particles that make up matter and how they interact with each other and with energy.
electron in the same way a particle with momentum would: It bumps the electron and changes the electron’s path. The light is also affected by the collision as though itwere a particle, in that its energy and momentum changes. Momentum is a quantity that can be defined for all particles. For light particles, or photons, momentum depends on the frequency, or color, of the photon, which in turndepends on the photon’s energy. The energy of a photon is equal to a constant number, called Planck’s cons...
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Meteorology.
to find the corresponding relative humidity and dew-point temperature. III SPECIAL METEOROLOGICAL INSTRUMENTS Meteorologists have developed several sophisticated instruments that measure multiple physical characteristics of the air simultaneously and at more than one location.The most important of these special instruments are radiosondes, Doppler radar, and weather satellites. A Radiosonde A radiosonde measures air temperature, air pressure, and humidity from the earth’s surface up to an alt...
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Cosmology - astronomy.
In 1917 American scientist Harlow Shapley measured the distance to several groups of stars known as globular clusters. He measured these distances by using amethod developed in 1912 by American astronomer Henrietta Leavitt. Leavitt’s method relates distance to variations in brightness of Cepheid variables, a class of starsthat vary periodically in brightness. Shapley’s distance measurements showed that the clusters were centered around a point far from the Sun. The arrangement of theclusters was...
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Inorganic Chemistry - chemistry.
two electrically charged plates (positively charged top plate and negatively charged bottom plate). By measuring the difference in how fast these electron-laden oildrops fell when the metal plates were charged and uncharged, Millikan was able to calculate the total charge on each oil drop. Because each measurement was a wholenumber multiple of -1.60 × 10 -19 coulombs, Millikan concluded this was the charge carried by a single electron. Using Thomson’s electron charge-to-mass ratio, Millikan then...
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Sun - astronomy.
A The Sun’s Place in the Milky Way The Milky Way Galaxy contains about 400 billion stars. All of these stars, and the gas and dust between them, are rotating about a galactic center. Stars that arefarther away from the center move at slower speeds and take longer to go around it. The Sun is located in the outer part of the galaxy, at a distance of 2.6 × 10 17 km (1.6 × 10 17 mi) from the center. The Sun, which is moving around the center at a velocity of 220 km/s (140 mi/s), takes 250 million y...
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Star (astronomy) - astronomy.
absorbing the missing colors of light. For example, the set of dark lines made by hydrogen includes a dark red line, the set of dark lines made by sodium includes a pairof dark yellow lines, and the set of dark lines made by iron includes lines of nearly every color. Each element in the gaseous outer layer of a star produces its ownparticular pattern of dark spectrum lines, depending on the temperature and pressure of the gas. Astronomers have observed spectrum lines, or spectra, for hundredsof...
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Atom
I
INTRODUCTION
Water Molecule
A water molecule consists of an oxygen atom and two hydrogen atoms, which are attached at an angle of 105°.
spontaneously break apart and change, or decay, into other atoms. Unlike electrons, which are fundamental particles, protons and neutrons are made up of other, smaller particles called quarks. Physicists know of six different quarks.Neutrons and protons are made up of up quarks and down quarks —two of the six different kinds of quarks. The fanciful names of quarks have nothing to do with their properties; the names are simply labels to distinguish one quark from another. Quarks are unique amo...
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Atom - chemistry.
Atoms have several properties that help distinguish one type of atom from another and determine how atoms change under certain conditions. A Atomic Number Each element has a unique number of protons in its atoms. This number is called the atomic number (abbreviated Z). Because atoms are normally electrically neutral,the atomic number also specifies how many electrons an atom will have. The number of electrons, in turn, determines many of the chemical and physical properties ofthe atom. The ligh...
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Space Exploration - astronomy.
to produce 250,000 newtons (56,000 lb) of thrust. The Germans launched thousands of V-2s carrying explosives against targets in Britain and The Netherlands. Whilethey did not prove to be an effective weapon, V-2s did become the first human-made objects to reach altitudes above 80 km (50 mi)—the height at which outer spaceis considered to begin—before falling back to Earth. The V-2 inaugurated the era of modern rocketry. A2 Early Artificial Satellites During the years following World War II, the...
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Trigonometry
I
INTRODUCTION
Trigonometry, branch of mathematics that deals with the relationships between the sides and angles of triangles and with the properties and applications of the
trigonometric functions of angles.
If point P, in the definition of the general trigonometric function, is on the y-axis, x is 0; therefore, because division by zero is inadmissible in mathematics, the tangent and secant of such angles as 90°, 270°, and -270° do not exist. If P is on the x-axis, y is 0; in this case, the cotangent and cosecant of such angles as 0°, 180°, and - 180° do not exist. All angles have sines and cosines, because r is never equal to 0. Since r is greater than or equal to x or y, the values of si...
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Neptune (planet) - astronomy.
The gaseous atmosphere of Neptune contains hydrogen, helium, and about 3 percent methane. It extends about 5,000 km (about 3,000 mi) above the planet’s ocean.Light reflected from Neptune’s deep atmosphere is blue, because the atmospheric methane absorbs red and orange light but scatters blue light. In 1998 astronomersalso identified molecules of methyl in Neptune’s atmosphere. Methyl molecules each contain one carbon atom and three hydrogen atoms. Methyl molecules are knownas hydrocarbon radical...
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Relativity
I
INTRODUCTION
Albert Einstein
In 1905 German-born American physicist Albert Einstein published his first paper outlining the theory of relativity.
in calculating very large distances or very large aggregations of matter. As the quantum theory applies to the very small, so the relativity theory applies to the verylarge. Until 1887 no flaw had appeared in the rapidly developing body of classical physics. In that year, the Michelson-Morley experiment, named after the American physicistAlbert Michelson and the American chemist Edward Williams Morley, was performed. It was an attempt to determine the rate of the motion of the earth through t...
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Rocket.
the vacuum of space, however, demonstrated that this belief was not true. In fact, rockets produce more thrust in the vacuum of space than on Earth. Air pressure andfriction with the air reduce a rocket’s thrust by about 10 percent on Earth as compared to the rocket’s performance in space. B Thrust and Efficiency Thrust is a measurement of the force of a rocket, or the amount of “push” exerted backward to move a rocket forward. Thrusts vary greatly from rocket to rocket.Engineers measure thrust...
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Rocket - astronomy.
the vacuum of space, however, demonstrated that this belief was not true. In fact, rockets produce more thrust in the vacuum of space than on Earth. Air pressure andfriction with the air reduce a rocket’s thrust by about 10 percent on Earth as compared to the rocket’s performance in space. B Thrust and Efficiency Thrust is a measurement of the force of a rocket, or the amount of “push” exerted backward to move a rocket forward. Thrusts vary greatly from rocket to rocket.Engineers measure thrust...
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Chemistry - chemistry.
parts of oxygen by weight, which is a ratio of about 1 to 8, regardless of whether the water came from the Mississippi River or the ice of Antarctica. In other words, acompound has a definite, invariable composition, always containing the same elements in the same proportions by weight; this is the law of definite proportions. Many elements combine in more than one ratio, giving different compounds. In addition to forming water, hydrogen and oxygen also form hydrogen peroxide.Hydrogen peroxide h...
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Sound
I
INTRODUCTION
Sound, physical phenomenon that stimulates the sense of hearing.
A fundamental law of harmony states that two notes an octave apart, when sounded together, produce a pleasant-sounding combination. Other combinations of notescan also be pleasing. Physically, an interval of a fifth consists of two notes, the frequencies of which bear the arithmetical ratio 3 to 2, and a major third, the ratio 5 to4. Fundamentally, the law of harmony states that two or more notes sound pleasant when played together if their frequencies bear small, whole number ratios; if thefreq...
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Diabetes Mellitus.
Once diabetes is diagnosed, treatment consists of controlling the amount of glucose in the blood and preventing complications. Depending on the type of diabetes, thiscan be accomplished through regular physical exercise, a carefully controlled diet, and medication. Individuals with Type 1 diabetes must receive insulin, often two to four times a day, to provide the body with the hormone it does not produce. Insulin cannot be takenorally, because it is destroyed in the digestive system. Consequent...
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Extrasolar Planets - astronomy.
When a planet passes in a front of the star it orbits—an event called a transit—it causes a small dip in the brightness of the star. Measuring the slight change in thebrightness can be used not only to directly detect a planet, but to determine its size and orbit. However, the planet needs to orbit in a plane that lies in a telescope’sline of sight on the star. Despite long odds, Earth-based telescopes have detected and studied a few exoplanets using this method. The first space telescope design...
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Relativity - astronomy.
beta, for example, might be as large as 0.5, and the mass of the electron doubled. The mass of a rapidly moving electron could be easily determined by measuring thecurvature produced in its path by a magnetic field; the heavier the electron, the greater its inertia and the less the curvature produced by a given strength of field ( see Magnetism). Experimentation dramatically confirmed Einstein's prediction; the electron increased in mass by exactly the amount he predicted. Thus, the kinetic ener...
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New York - geography.
The Adirondack province consists of a large highland area occupying 26,000 sq km (10,000 sq mi) in the northeastern quarter of the state. The region is domelike inshape, with the higher elevations toward the east. The western Adirondack province is more a rugged hill region and not truly mountainous. Geologically, this area isrelated to the Laurentian Upland, or Canadian Shield, which lies north of the St. Lawrence River, for it is composed of the same very old igneous rocks, principallygranite...
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New York - USA History.
The Adirondack province consists of a large highland area occupying 26,000 sq km (10,000 sq mi) in the northeastern quarter of the state. The region is domelike inshape, with the higher elevations toward the east. The western Adirondack province is more a rugged hill region and not truly mountainous. Geologically, this area isrelated to the Laurentian Upland, or Canadian Shield, which lies north of the St. Lawrence River, for it is composed of the same very old igneous rocks, principallygranite...