The law states that entropy increases during irreversible processes such as spontaneous mixing of hot and cold gases, uncontrolled expansion of a gas into a vacuum, and combustion of fuel. In popular, nontechnical use, entropy is regarded as a measure of the chaos or randomness of a system.

根据这一定律，在热气体与冷气体的自发混合、气体向真空的自由膨胀以及燃料的燃烧之类的不可逆过程中，熵都是增加的。在多数非科技使用上，熵被认为是一个混乱和漫无目系统的测量方式。

属类：自然科学-物理-

colloid : Substance consisting of particles that, although too tiny to be seen with the unaided eye (typically 1 nanometre to 10 micrometres), are substantially larger than atoms and ordinary molecules and that are dispersed in a continuous phase.

胶体:由比原子或普通分子大得多，但远小于肉眼可见的微粒组成的物质。这种粒子的大小大约在10-7～10-3公分，并且以各种方式连接或键合在一起。

属类：自然科学-物理-

Both the dispersed phase and the continuous phase may be solid, liquid, or gas; examples include suspensions, aerosols, smokes, emulsions, gels, sols, pastes, and foams. Colloids are often classified as reversible or irreversible, depending on whether their components can be separated.

通常，胶体粒子以分散物形态，存在于某种介质中，如空气中的烟雾粒子;但亦可单独存在，如橡胶。胶体一般分可逆和不可逆两种，取决于它们的组分是否可以分离。

属类：自然科学-物理-

Dyes, detergents, polymers, proteins, and many other important substances exhibit colloidal behaviour.

染料、洗涤剂、聚合物、蛋白质和许多重要物质都表现出胶体的行为。

属类：自然科学-物理-

Compression ratio: Degree to which the fuel mixture in an internal-combustion engine is compressed before ignition.

压缩比:在内燃机中，可燃混合气在点火前被压缩的程度。

属类：自然科学-物理-

It is defined as the volume of the combustion chamber with the piston farthest out divided by the volume with the piston in the full-compression position (see piston and cylinder).

它的定义是汽缸的最大工作容积(活塞离缸盖最远时)与活塞在充分压缩位置时的汽缸工作容积之比

属类：自然科学-物理-

A compression ratio of six means that the action of the piston compresses the mixture to one-sixth its original volume. A high ratio promotes efficiency but may cause engine knock.

。压缩比6，是指可燃混合气由于活塞在汽缸中的作用被压缩到原体积的1/6。高压缩比能提高效率，但也可能引起发动机爆震。

属类：自然科学-物理-

Compton effect: Change in wavelength of X rays and other energetic forms of electromagnetic radiation when they collide with electrons. It is a principal way in which radiant energy is absorbed by matter,

康普顿效应:电子对X射线和其它高能电磁辐射的弹性散射引起波长增大的现象;这是物质吸收辐射能的一种主要方式。

属类：自然科学-物理-

Conductor: Any of various substances that allow the flow of electric current or thermal energy. A conductor is a poor insulator because it has a low resistance to such flow. Electrical conductors are used to conduct electric current, as in the metal wires of an electric circuit.

导体:任何允许电流和热能流动的物质。导体可说是不良绝缘体，因为它的电阻很低。电导体用来导电，例如一个电路中的金属线。

属类：自然科学-物理-

Electrical conductors are usually metallic. Thermal conductors allow thermal energy to flow because they do not absorb radiant heat; they include materials such as metal and glass.

电导体一般是用金属制成的。热导体能使热能流动，因为它无法吸收辐射热;这类物质包括了金属和玻璃。

属类：自然科学-物理-

absolute zero :Temperature at which a thermodynamic system (see thermodynamics)has the lowest energy, 0 kelvin (K). It corresponds to-459.67°F (-273.15°C)and is the lowest possible temperature theoretically achievable by a system. A gas at constant pressure contracts as the temperature is decreased. A perfect gas would reach zero volume at absolute zero.

绝对零度:热力学系统能量最低时的温度，相当于-273.15℃或-459.67℉。当温度下降时，气体在恒定压力下会跟着收缩。理想气体在绝对零度时，体积会达到零。

属类：自然科学-物理-

However, a real gas condenses to a liquid or a solid at a temperature higher than absolute zero. At absolute zero, the system’s molecular energy is minimal and none is available for transfer to other systems. The Kelvin temperature scale has absolute zero as its zero point, and its fundamental unit is the kelvin.

不过，真实气体在未到绝对零度时已凝聚成液体或固体。在绝对零度下分子能量最小或近乎消失，不再具有可以转移给其它系统的能量。克尔文温标以绝对零度为其零点，它的基本单位是克尔文。

属类：自然科学-物理-

Acoustics: Science of production, control, transmission, reception, and effects of sound. Its principal branches are architectural, environmental, musical, and engineering acoustics, and ultrasonics.

声学:探讨声音之产生、控制、传达、接收及其效果的科学。声学主要分成建筑声学、环境声学、音乐声学、工程声学和超音波。

属类：自然科学-物理-

Environmental acoustics focuses on controlling noise produced by aircraft engines, factories, construction machinery, and general traffic. Musical acoustics deals with the design and use of musical instruments and how musical sounds affect listeners.

环境声学主要是研究噪音控制的问题，如喷射机引擎、工厂、重型建筑机械与汽车发出的声音，音乐声学研究的是乐器运作与设计的原理原则，以及乐声影响听众的方式

属类：自然科学-物理-

Engineering acoustics concerns sound recording and reproduction systems.

工程声学主要研究的是录音的发展以及原音重现系统

属类：自然科学-物理-

Ultrasonics deals with ultrasonic waves, which have frequencies above the audible range, and their applications in industry and medicine

超音波声学研究包括超音波之振动(频率高于可听得见的范围)以及工业和医学方面的应用

属类：自然科学-物理-

diffraction :Spreading of waves around obstacles. It occurs with water waves, sound, electromagnetic waves (see electromagnetic radiation), and small moving particles such as atoms, neutrons, and electrons, which show wavelike properties.

衍射:亦称绕射。波绕过障碍物向四周的扩展。声和电磁辐射(光、X射线、γ射线)能产生衍射，原子、中子、电子那样小的运动粒子也有衍射现象，这显示了这些粒子的类波特性。

属类：自然科学-物理-

When a beam of light falls on the edge of an object, it is bent slightly by the contact and causes a blur at the edge of the shadow of the object. Waves of long wavelength are diffracted more than those of short wavelength.

当一束光照到某物体的边缘时，光不再继续沿直线前进，而要在边缘处少许弯曲，致使物体阴影的边缘变得模糊。波长较长的波比波长较短的波易形成衍射。

属类：自然科学-物理-

Doppler effect : Apparent difference between the frequency at which waves-including light, sound, and radio waves-leave a source and that at which they reach an observer. The effect, first described by the Austrian physicist Christian Doppler (1803-1853), is caused by the relative motion of the observer and the wave source.

多普勒效应:由于观察者和波源的相对运动，使波(包括光波、音波和无线电波)在到达观察者时的频率和波离开波源时的频率发生差别。1842年奥地利物理学家都普勒(1803～1853)解释了这一效应。

属类：自然科学-物理-

It can be observed by listening to the blowing horn or siren of an approaching vehicle, whose pitch rises as the vehicle approaches the observer and falls as it recedes.

以声为例，当听者向吹响着的喇叭走近时，他听到的音调变高;在听者远离喇叭而去时，听到的音调变低。

属类：自然科学-物理-