基础阅读(物理专业英语).docx

基础阅读《物理专业英语》南京大学外文系公外英编商务印书馆1981L MATTER AND VOLUMEMatter is the name given to everything which has weight and occupies space. It may usually be detected by the sense of touch, sight or smell.Matter may exist in three states: solid, liquid and gas. Al 1 substanccs, cxccpt those which decompose when heatcd，may be changcd from one state into another. A substance in the liquid state may be changed into a gaseous substance. Changes can take place in the reverse order as well: gases may be changed into liquids and liquids into solids. A solid substance such as ice may be changed into the 1 iquid state, or liquefied, to become water; and this may be changed into gaseous state, or evaporated, to become steam.Steam may also be converted into water and water into ice.All matter occupies space. The space occupied by a quantity of matter is cal led its volume, and it is usual 1 y measured in units such as cubic meters or cubic ccntimetcrs. Solids have a definitc volume and shape, liquids have a definite volume but no shape; the latter take on the shape of the container in which they rest. Gases have no definite volume and no shape.2. SOUND MAY ECHOAn echo is produce when sound waves strike a surface and bounce back. Sound is ordinarily absorbed and changed to heat by most objects. But a hard wall or cliff will produce an echo. Outdoors an echo is often amusing, but in doors i t w i 11 cause you to hear the same soun d more tha n on ce, usual ly mixed with other sounds, and it will be irritating and confusing.In order to prevent echoes, wall and ceilings arc lined with soft drapes (窗帘)，porous (full of holes and space) wal 1 boards, or other materials which absorb the energy of sound. Broadcasting studios are always prepared in this way.Loudness of sound may be measured. There is a device for measuring the loudness of sound. It gives a reading on a dial in the number of sound units, called decibels, indicating the loudness of the sound. This device is useful in locating unwanted noises in schools, factories, and on the street.A form of the seime device is used to measure the faintest sound that a person can hear in order to measure his hearing ability. If one cannot hear as well as other people, he knows as result of this test what his hearing ability is. It is possible to day to have hearing aids which help greatly in overcoming loss of hearing.3. NEWTON， S LAWS OF MOTIONDynamics is one most essential foundation of physics. This subject was first soundly established in the 17tn century on the basis of the axiom usual ly known as Newton" s 1 aws of motion. Al though certain modif ications are now known to be necessary for the precise formulation of dynamics in accordance with modern developments, these laws arc sufficiently exaet for nearly all applications. A clear understanding of New to nian dynamics is of the first importance to every student of science and engineering.First Law- A body at rest rema ins at rest, and a body in motion moves with uniform speed in a straight line, unless a force acts on it.Second Law-Thc Tate of change of momcntum of a body is proportional to the impressed force and takes place in the direction of that force. By suit able choice of units one may say t hat the rate of change of momentum i s equal to the force.Third Law- If a force acts on a body then an equal and opposite force must act upon another body.In these laws "force，means the resultant of all externally applied forces. Momentum is the product of mass times velocity, thus for a body of constant mass, rate of change of momentum is equal to mass times acceleration. Force is often wrongly defined as mass times acceleration. As mass can vary in several circumstanccs this is unsound and misleading.These laws are fundamentally linked with the law of gravitation. The planets and satellites are the most familiar objects whose motions can be studied with preci si on. They do not move in straight 1 ines wi th unif onn speed, hence if we accept the first law we must suppose that they are acted upon by those forces which we call gravitational.4 ・ THE IDEAL GAS SCALEUntil about 1850 most measurements of temperature were made using mercury-in-glass thermometers, and physical laws were expressed on a mercury seale. As more precise measurements became possible it was found that diffcrcnt mercury thermomctcrs had slightly diffcrcnt scales and it became necessary to seek some more reliable than mercury ones, and there was close agreement between different gas scales over a wide range of temperatures. This agreement was found to be particularly close when working with 1 ow gas pressures. Kelvin proposed the use of an ideal gas, extrapolated to zero p. He showed that all the extrapolated gas scales derived from measurements on real gases must be identical. This then provides a fundamental scale which is the standard usually employed for theoretical purposes. This scale has an absolute zero at a finite number。