UNIT-3--Lesson-2-force-and-their-effects-市公开课一等奖省赛.pptx

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,UNIT 3Lesson 2 Forces and Their Effects,Terminology,Text tour,2025/11/7 周五,1,机械工程专业英语教程,1/23,Words and Expressions,2/23,Words and Expressions,3/23,4/23,Terminology,2025/11/7 周五,5,机械工程专业英语教程,Compressive,Serving to or able to compress,压缩：起压缩作用或能够压缩,Turning,The shaping of metal or wood on a lathe,车削：用车床将金属或木材加工成型过程,Lathe,车床,5/23,机械工程专业英语教程,2025/11/7 周五,Rectilinear,Moving in,consisting of,bounded by,or characterized by a straight line or lines:,直线：以直线运动，由直线组成，以直线为边，含有直线之特点,micromete,r,千分尺,6,6/23,2025/11/7 周五,7,机械工程专业英语教程,Thread,A helical or spiral ridge on a screw,nut,or bolt,螺纹：螺钉、螺母或螺栓上螺旋型凸棱,Shaper,牛头刨床,7/23,A study of any,machine or mechanism,shows 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,1,.,Thus,a study of mechanics and machines deals with forces and the effects of forces on bodies.,1,.work,在此指代“功”，,换句话说，这些机器在工作（做功）。在力作用下产生运动就实现了做功。,机械工程专业英语教程,2025/11/7 周五,Text tour,8,8/23,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 produces a stress in the part on which it is applied.Forces may be produced by an individual using,muscular action,or by machines with mechanical motion.,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 squeeze the object.Such a force is a,compressive force,.,机械工程专业英语教程,2025/11/7 周五,9,9/23,A third force is known as a,torsional force,or a,torque,since it tends to,twist an object,.Still another kind of force,which seems to make the layers or molecules of a material slide or slip on one another,is a,shearing force,.,Each of these forces may act,independently or in combination,.For example,a downward force applied on a vertical steel beam 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,.,机械工程专业英语教程,2025/11/7 周五,1010/23,The,turning of a part,in a lathe is another example of several forces in action(as shown in Figure 1).,1,2.,turning of a part,这里指“对一个零件进行车削加工”。,全句译为：几个力同时作用另外一个例子是在车床上对零件进行车削加工（如图,2.1,所表示）。,机械工程专业英语教程,2025/11/7 周五,Fig.2.1 The turning of a part in a lathe,11,11/23,As the work,revolves,and the,cutting tool,moves into the work,the,wedging action,of the,cutting edge,produces a shear force.This force causes the metal to seem to flow off the work in the form of,chips,.,2,3.chip,这里指“切屑”。,work,这里指“工件，即,workpiece”,。,全句可译为：这个力使得金属看起来像以切屑形式从工件上流出来一样。,If this,workpiece,is held between,the centers of the lathe,the centers exert a compressive force against the work.,3,4.centers of the lathe,意为“车床两个顶尖”。全句可译为：,假如一个工件被安装在车床两个顶尖之间，顶尖对工件施加一个压力。,机械工程专业英语教程,2025/11/7 周五,12,12/23,The,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.,Considerable 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 speeds.,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.,机械工程专业英语教程,2025/11/7 周五,13,13/23,The 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,and in devices to control motor speeds.,Centripetal force,causes an object to travel in circular path.This action is caused by the continuous 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 and opposite to the centrifugal force(see Fig.2.2).,机械工程专业英语教程,2025/11/7 周五,14,14/23,The materials used in the construction of rapidly moving machine parts and mechanisms must be structurally strong enough 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 tends to,pull,the parts,apart.,机械工程专业英语教程,2025/11/7 周五,15,15/23,Motion 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 around a center line and rectilinear motion is a straight line motion,rotary motion:,回转运动,rectilinear motion,：,直线运动,intermittent motion and reciprocating motion,：,间歇运动和往复运动,机械工程专业英语教程,2025/11/7 周五,16,16/23,Rotary 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 required to drill holes,turn parts in a lathe,mill surfaces,or drive a generator or fan belt.,4,5.,rotary motion,意为“回转运动”。全句可译为：,钻孔、在车床上车削零件、铣平面、驱动发电机或风扇带等都需要回转运动。,机械工程专业英语教程,2025/11/7 周五,17,17/23,Rectilinear Motion.,The feed of a tool on a lathe,the cutting of steel on a power saw,or the shaping of materials are 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 changed from rotary to rectilinear.,6,车床上刀具进给，在弓锯床上切削钢材或者采取牛头刨床进行刨削加工都属于直线运动做功。,以上三种方式中零件都将回转运动转变为直线运动进行做功。,6.,the screw of a micrometer,意为“千分尺中螺杆”,全句可译为：千分尺中螺杆和螺母中螺纹是把运动方向从转动变为直线另外一些应用实例。,机械工程专业英语教程,2025/11/7 周五,18,18/23,Harmonic 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 irregular motion,.For example,the fast return stroke of a power hacksaw or shaper ram is desirable because no cutting is done on the return stroke.Therefore,as more time is saved in returning the cutting tool to the working position,the less expensive is the operation.,7.,harmonic and intermittent motion,意为谐振运动和间歇运动。,8.,simple harmonic motion,意为“简谐运动”。全句可译为：,任何简单振动，比如摆下端有规律往复运动是简,谐运动。,机械工程专业英语教程,2025/11/7 周五,19,19/23,The combinations,of rotary and rectilinear motion obtainable,are unlimited,because of the large variety of parts such as,gears,cams,pulleys,screws,links,and belts,which can be combined in many arrangements.,机械工程专业英语教程,2025/11/7 周五,20,20/23,Summary,机械工程专业英语教程,2025/11/7 周五,21,1,、,Lexicologykey words,：,compressive,turning,lathe,rectilinear,micrometer,thread,shape,;,2,、,The Translation of Long Sentences.,21/23,英语谜语或脑筋急转弯（,Riddles,）,Q:,What is black when it is clean and white when it is dirty?,A:,A blackboard,Q:What is four feet on four feet waiting for four feet?,A:A cat on a chair waiting for a mouse,Q:Which three letters can frighten a thief away?,A:I C U,22/23,Q:What will you break once you say it?,A:Silence,Q:What always goes up and never goes down?,A:Your age,Q:Why did the boy make his dog sit in the sun?,A:He wants to have a hot dog.,Q:Which is faster,heat or cold?,A:Heat,because you can catch a cold,23/23,