2015同等学力英语阅读练习(20)

　　If a mother pushes her small son in a swing (秋千), giving only a light force each time he returns, eventually he will be swinging quite high. The child can do this for himself by using his legs to increase the motion, but both the mother’s push and the child’s leg movements must occur at the proper moment, or the extent of the swing will not increase. In physics, increasing the swing is increasing the amplitude ( 振幅 ); the length of the rope on the swing determines its natural oscillation ( 摆动 ) period. This ability of an object to move periodically or to vibrate when stimulated by a force operating in its natural period is called resonance.

　　Resonance is observed many times without consciously thinking about it; for example, one may find an annoying vibration or shimmy in an automobile, caused by a loose engine mount vibrating with increasing amplitude because of an out- of-round tire. The bulge ( 凸出部分) on the tire slaps the pavement with each revolution; at the natural resonance point of the engine mount, it will begin to vibrate. Such vibrations can result in considerable damage if allowed to persist. Another destructive example of resonance is the shattering of a crystal goblet by the production of a musical tone at the natural resonant point of the goblet. The energy of the sound waves causes vibration in the glass; as its amplitude increases, the motion in the glass exceeds the elasticity of the goblet, and it shatters.

　　An instrument called a tachometer (转速计) makes use of the principle of resonance. It consists of many tiny bars, loosely fastened together and arranged so that each bar can slide independently of the others. Movement of the bars causes changes in a dial. When placed next to a rotating motor or engine, the tachometer picks up slight vibrations which are transferred to the resonant bars. These bars begin to move, and the resulting dial may be read to find the revolutions per minute of the motor very quickly.

　　1. An object, if moving rhythmically when stimulated in a natural period, is said to __

　　[A] vibrate

　　[B] resonate

　　[C] swing

　　[D] oscillate

　　2. The distance a swing moves from its resting position is called its __

　　[A] revolution

　　[B] movement

　　[C] frequency

　　[D] amplitude

　　3. A tachometer is an instrument that uses resonance to determine

　　[A] the speed of a motor in revolutions

　　[B] the frequency at which a motor vibrates

　　[C] the amplitude of an engine that oscillates

　　[D] the changes in a dial within a car engine

　　4. An annoying vibration can be caused at the natural resonance of the car’s engine mount __

　　[A] if the engine moves too fast

　　[B] if the engine’s amplitude increases

　　[C] if a tire gets out of balance

　　[D] if damage occurs in the engine

　　5. In which of the following cases is it useful to consider the relationship between the length of an oscillating object and its natural period?

　　[A] Adjusting the speed of a car.

　　[B] Adjusting a clock pendulum.

　　[C] Adjusting tire balance.

　　[D] Adjusting engine mounts.

　　参考答案：

　　1.B 语义题。第一段的最后一句是这样定义的，物体在自然周期内受到力推动的作用下，产生周期性的运动或摆动，称为共振，因此本题选B。题干中的rhythmically意为“有节奏地”，其意思正好与文中的periodically(周期性地)相对应。

　　2.D 语义题。本题考查的是对词义的理解。第一段的倒数第二句解释到，在物理学上，增加秋千的摆动就是增加振幅，摇摆的绳子长度决定了它的自然摆动周期。因此本题选D，秋千从静止位置开始运动的距离称为振幅。A项的意思是“旋转，运行”，而B表示“运动”，C为“频率”，显然都不符合题意。

　　3.A 综合推断题。本文最后一段主要介绍的是转速计，转速计运用的是共振原理，它出很多小的转轴构成，每一个转轴都独立于其他转轴滑动。这些转轴的运动引起在刻度盘上的变化。把转速计放置在旋转的发动机或引擎旁边，转速汁就开始微微振动，并传输到共振转轴。这些转轴开始振荡后，很快就可以通过阅读刻度盘来了解发动机每分钟旋转的数了，因此本题选A，发动机旋转的速度。本题的关键是要理解这个转速计的原理。

　　4.C 信息明示题。题干的主语all annoying vibration可以在文章第二段找到，说的是由于轮胎不圆，振幅不断增大，引擎悬置脚在振荡中松动，这样就导致了汽车的反常振动或震颤。车胎上凸出的地方随着轮胎的转动拍打地面，当到了引擎悬置脚的共振点时，就会振动，可见本题选C，如果轮胎变形，就会导致汽车引擎脚的自然谐振反常振动。干扰项B说的是引擎的振幅增加，是错误选项。

　　5.B 综合推断题。本题要求找出能说明振荡物体长度和自然周期之间关系的例子。本题其实凭借基本的物理知识就能选出B(钟摆)。文中第一段也有提及，秋千绳子的长度决定着它的自然摆动周期。比较类似的情况就是钟摆，而汽车速度、轮胎形状和引擎悬置脚，物体本身的长度和周期之间都不能说明这种关系，因此都可以排除。