Вопрос № 1072609 - Английский язык

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Gravitation
1. Gravitation is a natural phenomenon by which physical bodies attract with a force proportional to their mass. In everyday life, gravitation is most familiar as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped. Gravitation causes dispersed matter to coalesce, and coalesced matter to remain intact, thus accounting for the existence of the Earth, the Sun, and most of the macroscopic objects in the universe.
2. Gravitation is responsible for keeping the Earth and the other planets in their orbits around the Sun; for keeping the Moon in its orbit around the Earth; for the formation of tides; for natural convection, by which fluid flow occurs under the influence of a density gradient and gravity; for heating the interiors of forming stars and planets to very high temperatures; and for various other phenomena observed on the Earth.
3. Gravitation is one of the four fundamental interactions of nature, along with electromagnetism, and the nuclear strong force and weak force. Modern physics describes gravitation using the general theory of relativity by Einstein, in which it is a consequence of the curvature of spacetime governing the motion of inertial objects. The simpler Newton's law of universal gravitation provides an accurate approximation for most physical situations.
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What determines the necessity of gravitation study by scientists?

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Flicker
1. The first requirement to be met in image analysis is that the reproduced picture shall not flicker, since flicker induces severe visual fatigue. Flicker becomes more evident as the brightness of the picture increases. If flicker is to be unobjectionable at brightness suitable for home viewing during daylight as well as evening hours, the successive illuminations of the picture screen should occur no fewer than 50 times per second. This is approximately twice the rate of picture repetition needed for smooth reproduction of motion. To avoid flicker, therefore, twice as much channel space is needed as would suffice to depict motion.
2. The same disparity occurs in motion picture practice, in which satisfactory performance with respect to flicker requires twice as much film as is necessary for smooth simulation of motion. A way around this difficulty has been found, in motion pictures as well as in television, by projecting each picture twice. In motion pictures, the projector interposes a shutter briefly between film and lens while a single frame of the film is being projected.
3. In television, each image is analyzed and synthesized in two sets of spaced lines, one of which fits successively within the spaces of the other. Thus the picture area is illuminated twice during each complete picture transmission, although each line in the image is present only once during that time. This technique is feasible because the eye is comparatively insensitive to flicker when the variation of light is confined to a small part of the field of view.  
4. It is thus possible to avoid flicker and simulate rapid motion by a picture rate of about 25 per second, with two screen illuminations per picture. The precise value of the picture-repetition rate used in a given region has been chosen by reference to the electric power frequency that predominates in the region.  
 (Encyclopedia Britannica)
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Why is it required to avoid flicker?

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Your weight is the force that you exert on the Earth. It is a result of gravity acting on your body. Weight differs from mass: your mass is constant whatever the force of gravity. Scientists measure mass in kilograms. This indicates the amount of matter in your body. Scientists measure weight in newtons (N), and 1 kg equals a force of 9.81 N. On the Moon your weight will be much less than it is on Earth because of the less gravity.
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What is your weight?

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Born in Edinburgh, the physicist James Clerk Maxwell has been described as the most brilliant scientist of the 1800s. His best-known work established a link between electromagnetism and light. This research later helped the German physicist Heinrich Hertz to build the first radio-wave transmitter. During his carrier, Maxwell produced new theories on many scientific problems of the day: the physical properties of gases; the nature of the planet Saturn’s rings; how humans perceive colors.
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What link did James Clerk Maxwell establish?

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The Italian scientist Luigi Galvani spent much of his life studying electricity. He found out that a dead frog’s legs contract when they are attached to an iron board by brass hooks. He suspected that there was electricity in the frog’s muscles, which he named animal electricity. Another Italian scientist, Alessandro Volta, challenged this idea. He believed that the two metals had reacted together to make the electricity. Neither theory was entirely correct. Galvani also carried out experiments with electric charges. An instrument for measuring electric current is called a galvanometer in his honor.

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Rays of light like all forms of energy that travel in waves can be reflected. Light rays are reflected. Light rays are reflected when they hit a shiny or silvered surface, such as a still pool of water or a mirror. Reflection involves two light rays and the reflected, or outgoing, ray, which bounces off the reflecting surface. The two rays are at identical angles to the reflecting surface on either side of an imaginary line.