Lesson 2 force and their effects

1、UNIT 3Lesson 2 Forces and Their Effects Terminology Text tour 2022-5-131機械工程專業(yè)英語教程Words and ExpressionsWords and ExpressionsTerminology2022-5-135機械工程專業(yè)英語教程 Compressive Serving to or able to compress 壓縮的：起壓縮作用或能夠壓縮的 Turning The shaping of metal or wood on a lathe 車削：用車床將金屬或木材加工成型的過程 Lathe 車床機械工程專業(yè)英語教

2、程2022-5-13RectilinearMoving in, consisting of, bounded by, or characterized by a straight line or lines:直線的：以直線運動的，由直線組成的，以直線為邊的，具有直線之特點的 micrometer 千分尺 6 2022-5-137機械工程專業(yè)英語教程Thread A helical or spiral ridge on a screw, nut, or bolt 螺紋：螺釘、螺母或螺栓上螺旋型的凸棱Shaper牛頭刨床A study of any machine or mechanism sho

3、ws that each is made up of a number of movable parts. These parts transform a given motion to a desired motion. In other words, these machines perform work. Work is done when motion results from the application of force. Thus, a study of mechanics and machines deals with forces and the effects of fo

4、rces on bodies.機械研究表明，所有的機器都是由大量活動件構成的。這些構件將給定的運動轉化為所需要的運動形式。換句話說，這些機器在工作。在力的作用下，機器才能進行工作。因而，力學和機械學是研究力以及其對物體作用的。 機械工程專業(yè)英語教程2022-5-13Text tour8 A force is a push or pull. The effect of a force either changes the shape or motion of a body or prevent other forces from making such changes. Every force

5、produces a stress in the part on which it is applied. Forces may be produced by an individual using muscular action or by m a c h i n e s w i t h m e c h a n i c a l m o t i o n . 力有推力和拉力之分。力或改變物體的外形或運動形式或防止諸如此類的變化。每個力都會在其作用的物體上產(chǎn)生應力。不論 是 人 為 的 動 作 或 是 機 器 的 機 械 運 動 都 可 能 產(chǎn) 生 力 。 機械工程專業(yè)英語教程2022-5-139

6、 Forces are produced by physical or chemical change, gravity, or changes in motion. When a force is applied which tends to stretch an object, it is called a tensile force. A part experiencing a tensile force is said to be in tension. A force can also be applied which tends to shorten or s q u e e z

7、e t h e o b j e c t . S u c h a f o r c e i s a compressive force. 物理或化學反應，地心引力的吸引，或是機器運轉形式的變化都會產(chǎn)生力。拉伸物體的力稱作拉力。我們認為拉力作用的物體，承受拉應力。力也可以縮短或擠壓一個物體，這樣的力稱作壓力。 機械工程專業(yè)英語教程2022-5-1310 A third force is known as a torsional force, or a torque since it tends to twist an object. Still another kind of force, whic

8、h seems to make the layers or molecules of a material slide or slip on one another, is a shearing force. 第三種力因為它有使扭轉物體的趨向，稱為扭轉力或是扭矩 。還有另外一種使材料截面層發(fā)生滑移的力，稱為剪切力。機械工程專業(yè)英語教程2022-5-1311Each of these forces may act independently or in combination. For example, a downward force applied on a vertical steel b

9、eam tends to compress the beam. If this beam is placed in a horizontal position and a load is applied in the middle, the bottom of the beam tends to stretch and is in tension. At the same time, the top area is being pushed together in compression. If the compressive and tensile forces are greater en

10、ough to make the layers of the material slide upon each other, a shearing force results. 各種力可能單獨或者結合在一起對物體產(chǎn)生作用。 例如，對一個豎直放置的橫梁施加一個向下的力會壓縮橫梁。如果在水平放置橫梁的中間部位施加負載，那么橫梁的底端拉伸，正承受拉應力。同時，橫梁的頂部在壓應力的作用下壓縮聚集。如果壓力和拉力大小能夠使得使材料層截面發(fā)生滑移，則剪切力產(chǎn)生。The turning of a part in a lathe is another example of several forces in

11、action (as shown in Figure 1).1turning of a part 這里指“對一個零件進行車削加工”。1. 全句譯為：幾個力同時作用的另外的一個例子是在車床上 對 零 件 進 行 車 削 加 工 （ 如 圖 1 所 示 ） 。機械工程專業(yè)英語教程2022-5-13Fig. 1 The turning of a part in a lathe 13As the work revolves and the cutting tool moves into the work, the wedging action of the cutting edge produces

12、a shear force. This force causes the metal to seem to flow off t h e w o r k i n t h e f o r m o f c h i p s . 2 2. chip 這里指“切屑”。work 這里指“工件，即 workpiece ”。全句可譯為：這個力使得金屬看起來像以切屑的形式從工件上流出來一樣。If this workpiece is held between the centers of the lathe, the centers exert a compressive force against the wo

13、rk.33. centers of the lathe 意為“車床的兩個頂尖”。全句可譯為：如果一個工件被安裝在車床的兩個頂尖之間，頂尖對工件施加一個壓力。機械工程專業(yè)英語教程2022-5-1314The lathe dog which drives the work tends to produce a shearing force. The pressure of the cutting tool against the work produces tension and compression, as well as a shearing action.控制工件的車床夾頭給工件一個剪切力

14、。切削工具給工件的壓力產(chǎn)生了拉伸，壓縮和剪切作用。機械工程專業(yè)英語教程2022-5-1315Considerable attention is given to the action of centrifugal force in grinding wheels. That is, the bonding agent that holds the abrasive particles on the wheel must be stronger than the forces which tend to make the revolving wheel fly apart at high spe

15、eds. For this reason, the speed of a grinding wheel should not exceed the safe surface speed limit specified by the manufacturer. Centrifugal force increases with speed.要注意砂輪的離心力作用。即砂輪上磨料粒子與粘合劑的粘合強度，一定要高于，高速旋轉的砂輪對其產(chǎn)生的離心力。正因如此，砂輪的轉速一定不能超過供應商注明的表面安全速 度 極 限 。 速 度 提 高 ， 離 心 力 增 大 。機械工程專業(yè)英語教程2022-5-1316T

16、he principles of centrifugal force are used in design of centrifuge-type machines. Some centrifuges are used to separate chemicals; others are used to remove impurities in metal by centrifugal casting processes. Centrifugal force principles are also used in common appliances such as clothes dryers a

17、nd in devices to control motor speeds and accelerate moving machines.離心機的設計利用了離心力原理。一些離心機用來分離化學物質；有些在鑄造時通過離心鑄造法來去除金屬中的雜質。離心力原理在普通設備中也有應用，例如，衣物甩干機，通過 控 制 設 備 中 電 機 的 轉 速 為 運 動 件 加 速。機械工程專業(yè)英語教程2022-5-1317Centripetal force causes an object to travel in circular path. This action is caused by the contin

18、uous application of forces which tend to pull the object to the center. In other words, the inward force which resists the centrifugal force is called the centripetal force. The centripetal force of objects spinning at a constant rate produces an acceleration toward the center which is equal a n d o

19、 p p o s i t e t o t h e c e n t r i f u g a l f o r c e .向心力使得物體作圓周運動。將物體拉向中心的力，使物體進行圓周運動。換句話說，抵抗離心力作用并指向物體內(nèi)部的力稱為向心力。向心力使勻速圓周運動的物體產(chǎn)生了一個向心加速度，離心力與向心力大小相等方向相反。機械工程專業(yè)英語教程2022-5-1318The materials used in the construction of rapidly moving machine parts and mechanisms must be structurally strong enough

20、to provide the centripetal force required to hold the parts to a circular path. At the same time, the materials must be able to withstand the centrifugal force which rends to pull the parts apart. 零件進行圓周運動必須要有向心力作用，因此高速運轉的機器零件和機械裝置所使用的材料的結構強度，必須能夠保證該向心力。同時，材料強度也必須能夠承受離心力的作用。機械工程專業(yè)英語教程2022-5-1319Moti

21、on and the basic laws which affect motion are important considerations because of the numerous applications of these principles to produce work through mechanical devices. There are two primary mechanical motions: rotary and rectilinear. These terms suggest that rotary motion is a circular movement

22、around a center line and rectilinear motion is a straight line motion. For either rotary or rectilinear motion, it is possible, with added mechanical devices, to produce other forms of motion such as intermittent motion and reciprocating motion.因為大多數(shù)機械運動原理和影響機械運動的基本規(guī)律的應用，都是通過機械設備實現(xiàn)生產(chǎn)工作的，因此這些原理要著重關注。

23、有兩種基本的機械運動方式：回轉運動和直線運動。這兩種運動可理解為：回轉運動是設備繞其中心線進行的圓周運動，直線運動是設備沿一條直線的運動。對更多的機械設備來說，不管是回轉運動還是直線運動，可能會產(chǎn)生其他的運動形式像間歇運動和往復運動。機械工程專業(yè)英語教程2022-5-1320Rotary Motion. The motion that is commonly transmitted is rotary motion. This type of motion may be produced with hand tools or power tools. Rotary motion is requ

24、ired to drill holes, turn parts in a lathe, mill surfaces, or drive a generator or fan belt.4 4. rotary motion 意為“回轉運動”。全句可譯為：鉆孔、在車床上車削零件、銑平面、驅動發(fā)電機或風扇的帶等都需要回轉運動。機械工程專業(yè)英語教程2022-5-1321Rectilinear Motion. The feed of a tool on a lathe, the cutting of steel on a power saw, or the shaping of materials ar

25、e all situations in which rectilinear or straight line motion produces work. In each of these situations a part or mechanism is used to change rotary motion to straight line motion. The screw of a micrometer and the threads in a nut are still other applications where the direction of motion is c h a

26、 n g e d f r o m r o t a r y t o r e c t i l i n e a r . 5 車床上車刀的進刀，電鋸鋼材的切削或者材料的刨削都是以直線或是直線運動方式加工工件。在以上的每一種方式中，零件或機械裝置都將回轉運動轉變?yōu)橹本€運動。5. the screw of a micrometer 意為“千分尺中的螺桿”全句可譯為：千分尺中的螺桿和螺母中的螺紋是把運動方向從轉動變?yōu)橹本€的另外一些應用實例。機械工程專業(yè)英語教程2022-5-1322Harmonic and Intermittent Motion.6 Any simple vibration, such as the regular back-and-forth movement of the end of a pendulum, is simple harmonic motion.7 However, many manufacturing processes require intermittent or irregu