English – Russian translation

Date: 2015-10-07; view: 518.

TRANSLATION

1. Scientists have found some experimental evidence for dark matter. Astronomers at Bell Labs in the United States found evidence for dark matter in an image taken by the Hubble Space Telescope (HST) in 1997. Light from a cluster of galaxies in the image was bent by another cluster of galaxies in the foreground of the picture. By making computer models of the cluster in the foreground and matching them to the way it bent the light of the background cluster in the image, the scientists were able to estimate the mass of the foreground cluster. The model that fit best showed that the cluster's mass was about 250 times as great as the mass of just the visible part of the cluster.

2. A physical change is a change in matter that involves no chemical reaction. When a substance undergoes a physical change, the composition of its molecules remains unchanged, and the substance does not lose its chemical identity. Melting, evaporating, and freezing are three types of physical change. For example, water (H₂O) is a liquid that freezes to form the solid ice, which may again be melted into water. Because molecules of water and ice are composed of the same chemical elements in the same proportions, the change from water to ice is a physical change. Physical changes include any alteration in the shape and size of a substance. For example cutting, grinding, crushing, annealing, dissolving, or emulsifying produce physical changes. Still another physical change is sublimation, the change from a solid to a gas.

3. When a substance undergoes a chemical change, the composition of its molecules changes. The properties of the original substance are lost, and new substances with new properties are produced. An example of a chemical change is the production of rust (iron oxide) when oxygen in the air reacts with iron. Chemical changes may also result in physical changes. For example, when wood (a solid) is burned, it is combined with oxygen gas to produce gaseous carbon dioxide (CO2), liquid water, and solid carbon.

4. In the United States and Britain, the everyday units of linear measurement have been the inch, foot, yard, and mile. Until recently in Britain, the English units of length were defined in terms of the imperial standard yard, which was the distance between two lines on a bronze bar made in 1845 to replace an earlier yard bar that had been destroyed by fire in 1839. Because the imperial standard yard bar has been shrinking at the rate of 1.5 millionths of an inch per year, the United States adopted a copy of the international prototype meter as the national standard of length in 1889. Until 1960, all U.S. measurements of length were derived from a standard meter (meter prototype number 27). In 1960 the meter was redefined in terms of wavelengths of light from a krypton-86 source. In 1983 it was again redefined as the length of the path traveled by light in a vacuum in 1/299,792,458 of a second.

5. English units of weight (ounces, pounds, and tons) are now also derived from the metric standard of mass, which is the international prototype kilogram. This is a solid cylinder of platinum-iridium alloy maintained at constant temperature at Sevres near Paris. A copy, as exact as possible, of this standard is maintained by an agency of the U.S. Department of Commerce. Most countries have converted or are in the process of converting their local systems of weights and measures to the metric system. Some old terms, however, may continue in use.

(From different sources)