机械工程专业英语课件L01.ppt

课件,1,English for Mechanical Engineering,机械工程专业英语,常州工学院机电工程学院徐红丽,课件,2,机械工程专业英语,预备知识,一、Background Information,CHAPTER 1 MATERIALS AND HOT WORK,Lesson 1 Basic Concepts in Mechanics,In rational mechanics, mechanical work is the amount of energy transferred by a force acting through a distance. Like energy, it is a scalar quantity, with SI units of joules. The term work was first coined in the 1830s by the French mathematician Gaspard-Gustave Coriolis.,The mechanical work applied to an object can be calculated from the dot product of the applied force (F) and the displacement (d) of the object.,Work ：,International System of Units(SI),课件,3,机械工程专业英语,一、Background Information,Lesson 1 Basic Concepts in Mechanics,A baseball pitcher does positive work on the ball by transferring energy into it .,预备知识,课件,4,机械工程专业英语,一、Background Information,Lesson 1 Basic Concepts in Mechanics,Efficiency,Mechanical Efficiency is the ratio of work input to work output. It is often expressed as a percentage. The efficiency of an ideal machine is 100 % but an actual machines efficiency will always be less than 100% because of the Second law of thermodynamics which states that the quality of energy will decay, eventually becoming heat. This means that some of the work put into the system is transformed (lost) into thermal energy (heat). In a mechanical system, friction is the most common cause of the work lost to heat.,预备知识,课件,5,机械工程专业英语,一、Background Information,Lesson 1 Basic Concepts in Mechanics,Mechanical Advantage,In physics and engineering, mechanical advantage (MA) is the factor by which a mechanism multiplies the force or torque put into it. Generally, the mechanical advantage is calculated as follows:,or more simply:,预备知识,课件,6,Mechanical Advantage：,机械工程专业英语,Lesson 1 Basic Concepts in Mechanics,预备知识,课件,7,Mechanical Advantage：,机械工程专业英语,Lesson 1 Basic Concepts in Mechanics,预备知识,课件,8,机械工程专业英语,词 汇,Lesson 1 Basic Concepts in Mechanics,二、Words and Expressions,mechanics mikniks n. 机械学，力学. abbr. mech.modify mCdifai v. 修改，调解，变更manageable 5mAnidVEbl adj.可控制的、易处理的、便于管理的incline in5klain vt. （使）倾斜 vi. 倾斜，倾向 n. 倾斜，斜坡，斜面ramp rAmp n. 斜板,斜坡, 敲诈vi. 狂跳乱撞, 敲诈, 蔓延 vt.使有斜面, 敲诈slope slEup n.斜坡, 斜面, 倾斜 v. (使)顺斜 ramp slope 斜坡坡度,课件,9,机械工程专业英语,Lesson 1 Basic Concepts in Mechanics,二、words and Expressions,friction 5frikFEn n. 摩擦, 摩擦力roll 5rEul vt.滚动, 滚转, (使)摇摆, (使)摇晃, 卷起, 卷拢,辗, 轧 n.卷, 卷形物, 摇晃, 摆动, 名单multiplier 5mQltiplaiE n.放大器，乘法broom bru:m n. 扫帚 植金雀花 vt. 扫除 broomcorn 高粱 broomrape 肉苁蓉 A new broom sweeps clean 新官上任三把火convert kn5vE:t n.皈依者 vt.使转变, 转换.,使.改变信仰handle 5hAndl n.手柄 vt.触摸, 运用, 买卖, 处理, 操作 n.计句柄,词 汇,课件,10,机械工程专业英语,Lesson 1 Basic Concepts in Mechanics,二、words and Expressions,sweep swi:p v. 清扫, 席卷, 掠过，斜坡，斜面efficiency i5fiFEnsi n. 效率，功效 efficient adj. efficiently adv.gauge geIdV v.测量，校验 n.标准尺, 规格, 量规, 量表bearing 5bZEriN n. 轴承, 关系, 方面, 意义, 方向ideal mechanical advantage d5va:ntidV 理想的机械效益 neglect ni5glekt vt.忽略，忽视 n. neglect of duty 疏于职守 negligible 5neglidVEbl adj. 可以忽略的，不予重视的,词 汇,课件,11,Work is defined as force multiplied by the distance over which the force acts. Work is measured in metre-kilograms. A metre-kilogram equals the work done by a force of one kilogram acting through a distance of one metre. For example, if a work task involves lifting a 300 kilogram machine two and one half metres into a truck, then 750 metre kilograms of work is required. Since no humans can lift 300 kilograms directly, a device must be employed to modify the required effort into something manageable.,机械工程专业英语,Lesson 1 Basic Concepts in Mechanics,课文分析,课件,12,机械工程专业英语,Work is defined as force multiplied by the distance over which the force acts. Work is measured in metre-kilograms.,功的定义是力乘以沿力的作用方向物体移动的距离。功的单位用公斤米来表示。,Lesson 1 Basic Concepts in Mechanics,A metre-kilogram equals the work done by a force of one kilogram acting through a distance of one metre.,l公斤米等于1公斤力作用于物体上使物体移动l米的距离所作的功。,课文分析,课件,13,机械工程专业英语,For example, if a work task involves lifting a 300 kilogram machine two and one half metres into a truck, then 750 metre kilograms of work is required.,例如，一项任务需要将一台300公斤重的设备提升到2.5米高的卡车上，那么就需要做750公斤米的功 。,Since no humans can lift 300 kilograms directly, a device must be employed to modify the required effort into something manageable.,Lesson 1 Basic Concepts in Mechanics,课文分析,由于没有人能直接举起300公斤的重物，因此必须使用一种设备将所需的作用力转变成人力所能及的。,课件,14,机械工程专业英语,One common device is an inclined plane- in this case, a loading ramp that slopes from the ground to the truck, If the ramp were 10 metres long and friction forces were negligibly small, then 75 kilograms of force would be required to roll the machine up the ramp. The total work is still 750 metre-kilograms (10 metres multiplied by 75 kilograms), but the effort has been modified so that the maximum force required is only 75 kilograms.,Lesson 1 Basic Concepts in Mechanics,课文分析,课件,15,机械工程专业英语,One common device is an inclined plane- in this case, a loading ramp that slopes from the ground to the truck, If the ramp were 10 metres long and friction forces were negligibly small, then 75 kilograms of force would be required to roll the machine up the ramp.,Lesson 1 Basic Concepts in Mechanics,neglidbladj.可以忽略的; 无足轻重的;,课文分析,常用的装置是一个斜面-在这个例子中，一个倾斜在地面和卡车之间的承载斜板，如果斜板有10米长，摩擦力很小可忽略不计的话 ，那么就只需要75公斤的力将机器滚上斜板。,课件,16,机械工程专业英语,The total work is still 750 metre-kilograms (10 metres multiplied by 75 kilograms), but the effort has been modified so that the maximum force required is only 75 kilograms.,Lesson 1 Basic Concepts in Mechanics,总功仍然是750公斤米(用75公斤乘以10米)，但作用力已经被改变，于是其所需的最大外力仅仅是75公斤。,课文分析,课件,17,A device that decreases the necessary applied force while increasing the distance over which the smaller force acts is called a force multiplier. Machines can also multiply speed and distance. A broom is an example of a speed and distance multiplier because it converts input force and distance at the handle into a lower force and larger distance at the sweeping end. Since the larger distance at the sweeping end is covered in the same time as the input distance, then the speed is also increased. In addition to modifying forces and distances, machines can also change the direction of motion.,机械工程专业英语,Lesson 1 Basic Concepts in Mechanics,课文分析,课件,18,机械工程专业英语,A device that decreases the necessary applied force while increasing the distance over which the smaller force acts is called a force multiplier.,使所需的作用力减少，同时这个较小的作用力使所通过的距离增加，这样的装置被称为力放大器（省力器）。,Machines can also multiply speed and distance.,机器装置也可放大速度和距离。,Lesson 1 Basic Concepts in Mechanics,课文分析,课件,19,机械工程专业英语,A broom is an example of a speed and distance multiplier because it converts input force and distance at the handle into a lower force and larger distance at the sweeping end.,扫帚就是一个速度和距离放大器的例子。因为它把在手柄上输入的力和距离，在扫帚的尾部转变成较小的力和较长的距离。,Lesson 1 Basic Concepts in Mechanics,课文分析,课件,20,机械工程专业英语,Since the larger distance at the sweeping end is covered in the same time as the input distance, then the speed is also increased.,由于在相同的时间里扫帚的尾部比输入端走过距离大，因此尾部的速度也就增加了。,In addition to modifying forces and distances, machines can also change the direction of motion.,机械装置除了能放大力和距离之外，也能改变运动的方向。,Lesson 1 Basic Concepts in Mechanics,课文分析,课件,21,Efficiency and mechanical advantage are used to gauge the performance of mechanical machines. Efficiency is defined as the useful mechanical output work, expressed as a percentage of the input work. Efficiency is always less than 100 percent because of friction between moving parts. If someone actually wheeled the machine of the initial example up the ramp, they might discover that it required 84 kilograms. The nine kilograms difference is the force required to overcome the resistance of the wheels and bearings. Under these conditions the machine would have an efficiency of 89 percent.,机械工程专业英语,Lesson 1 Basic Concepts in Mechanics,课文分析,课件,22,机械工程专业英语,Efficiency and mechanical advantage are used to gauge the performance of mechanical machines.,效率和机械效益是用来衡量机械装置性能的。,Efficiency is defined as the useful mechanical output work, expressed as a percentage of the input work.,效率定义为输出的有用的机械功占输入功的百分率来表示。,Lesson 1 Basic Concepts in Mechanics,课文分析,课件,23,机械工程专业英语,Efficiency is always less than 100 percent because of friction between moving parts.,效率总是要低于100，因为相对运动零件之间存在摩擦。,If someone actually wheeled the machine of the initial example up the ramp, they might discover that it required 84 kilograms.,像开始所举的那部机器的例子那样，如果有人真的把该机器滚上斜板，他们可能发现那要花84公斤的力。,Lesson 1 Basic Concepts in Mechanics,课文分析,课件,24,机械工程专业英语,The nine kilograms difference is the force required to overcome the resistance of the wheels and bearings.,这9公斤力的差额就是用于克服滚轮和轴承之间阻力。,Lesson 1 Basic Concepts in Mechanics,Under these conditions the machine would have an efficiency of 89 percent.,在这种情况下该机械装置将只有89的效率。,课文分析,课件,25,If they slid the refrigerator up the ramp without wheels, the required force could be 215 kilograms or more, which corresponds to an efficiency of less than 35 percent. Ideal mechanical advantage neglects friction and is equal to the distance the input force travels divided by the useful distance the load travels. For force multiplying machines, the input distance is greater than the load distance and the ideal mechanical advantage is greater than 1. In the loading ramp example, the ideal mechanical advantage is 4 ,since the input distance is 10 metres (the length of the ramp) and the useful load distance is two and one-half metres (the vertical distance the load travels).,机械工程专业英语,Lesson 1 Basic Concepts in Mechanics,课文分析,课件,26,机械工程专业英语,If they slid the refrigerator up the ramp without wheels, the required force could be 215 kilograms or more, which corresponds to an efficiency of less than 35 percent.,如果在没有滚轮情况下，把冰箱滑上斜板，所需的力可能是215公斤或更大，那么相应的机械效率就小于35。,Lesson 1 Basic Concepts in Mechanics,课文分析,课件,27,机械工程专业英语,Ideal mechanical advantage neglects friction and is equal to the distance the input force travels divided by the useful distance the load travels.,理想的机械效益是忽略摩擦损失，等于输入力移动的距离除以负载移动的有效距离。,Lesson 1 Basic Concepts in Mechanics,For force multiplying machines, the input distance is greater than the load distance and the ideal mechanical advantage is greater than 1.,对于力放大装置，输入的距离要比负载的距离大，因而理想的机械效益是比1要大的。,课文分析,课件,28,机械工程专业英语,In the loading ramp example, the ideal mechanical advantage is 4, since the input distance is 10 metres (the length of the ramp) and the useful load distance is two and one-half metres (the vertical distance the load travels).,在承载斜板例子中，该理想机械效益是4，因为该输入距离是10米(斜板长度)，而有效负载移距是25米(该负载移动的垂直距离)。,Lesson 1 Basic Concepts in Mechanics,课文分析,课件,29,An inclined plane is always a force multiplying machine. For speed-multiplying machines the input distance is less than the load distance and the ideal mechanical advantage is less than 1. Machines that simply change the direction of motion have an ideal mechanical advantage equal to 1. The actual mechanical advantage includes friction and is equal to the actual output force divided by the actual input force. The actual mechanical advantage in the loading ramp example is about 3.6 with wheels and about 1.4 without wheels.,机械工程专业英语,Lesson 1 Basic Concepts in Mechanics,课文分析,课件,30,机械工程专业英语,An inclined plane is always a force multiplying machine.,斜面就是一个力放大装置。,Lesson 1 Basic Concepts in Mechanics,For speed-multiplying machines the input distance is less than the load distance and the ideal mechanical advantage is less than 1.,对于速度放大装置，输入距离要比负载距离小，而理想的机械效益亦比1要小。,课文分析,课件,31,机械工程专业英语,Machines that simply change the direction of motion have an ideal mechanical advantage equal to 1.,仅仅改变运动方向的机器装置具有一个等于l的理想机械效益。,Lesson 1 Basic Concepts in Mechanics,The actual mechanical advantage includes friction and is equal to the actual output force divided by the actual input force.,实际机械效益包括了摩擦损失并等于实际输出力除以实际输入力。,课文分析,课件,32,机械工程专业英语,The actual mechanical advantage in the loading ramp example is about 3.6 with wheels and about 1.4 without wheels.,在承载斜板例子中的实际机械效益在有滚子条件下，大约是3.6，无滚子条件下，大约是1.4。,Lesson 1 Basic Concepts in Mechanics,课文分析,