专业英语资料1.docx

1、专业英语资料1Chapter 1Basic Concepts in Mechanic1. ForceIn simple terms, a force is a push or a pull. Force may be caused by electromagnetism, gravity, or a combination of physical means.2. Net forceNet force is the vector sum of all forces that act on an object, including friction and gravity. When force

2、s are applied in the same direction they are added. For example, if two 10N forces were applied in the same direction the net force would be 20N.If 10N of force were applied in one direction and 20N of force applied in the opposite direction, the net force would be 10N and object would move in the d

3、irection of the greater force. If 10N of force were applied equally in both directions, the net force would be zero and the object would not move.3. TorqueTorque is a twisting or turning force that causes an object to rotate. For example, a force applied to the end of a lever causes a turning effect

4、 or torque at the pivot point. Torque (M) is the product of force and radius (lever distance).M=Force RadiusIn the English system torque is measured in pound-feet (1b-ft) or pound-inches (N-in). If 10N of force were applied to a lever 1ft long, for example, there would be 10N-ft of torque.An increas

5、e in force or radius would result in a corresponding increase in torque. Increasing the radius to two ft, for example, result in 201b-ft torque.4. SpeedAn object in motion travels a distance in a given time. Speed is the ratio of the distance traveled and the time it takes to travel the distance.Spe

6、ed = Distance / Time5. Linear SpeedThe linear speed of an object is a measure of how long it takes the object to get from point A to point B. linear speed is usually given in a form such as meters per second (m/s). For example, if the distance between point A and point B were 10 meters, and it took

7、2 second to travel the distance, the speed would be 5m/s.6. Angular (Rotational) SpeedThe angular speed of a rotating object is a measurement of how long it takes a given point on the object to make one complete revolution from its starting point. Angular speed is generally given in revolutions per

8、minute (rad/min). An object that makes ten complete revolutions in one minute, for example, has a speed of 62.8rad/min.7. Acceleration An object can change speed. An increase in speed is called acceleration. Acceleration occurs only when there is a change in the force acting upon the object. An obje

9、ct can also change from a higher to a lower speed. This is known as deceleration (negative acceleration).A rotating object, for example, can accelerate from 62.8rad/min to 12.56rad/min, or decelerate from 125.6rad/min to 62.8rad/min.8. InertiaMechanical systems are subject to the law of inertia. The

10、 law of inertia states that an object will tend to remain in its current states of rest or motion unless acted upon by an external force. This property of resistance to acceleration / deceleration is referred to as the moment of inertia. The English system of measurement is pound-feet squared (1b-ft

11、2).If we look at a continuous roll of paper, for example, we know that when the roll is stopped it would take a certain amount of force to overcome the inertia of the roll to get it rolling. The force required to overcome this inertia can come form a source of energy such as a motor. Once rolling, t

12、he paper will continue unwinding until another force acts on it to bring it to a stop.9. Friction A large amount of force is applied to overcome the inertia of the system at rest to start it moving. Because friction removes energy from a mechanical system, a continual force must be applied to keep a

13、n object in motion. The law of inertia is still valid, however, since the force applied is needed only to compensate for the energy lost.Chapter 2Kinds of SteelsThere are two general kinds of steels: carbon steel and alloy steel. Carbon steel contains only iron and carbon, while alloy steel contains

14、 some other “ alloying elements” such as nickel(镍), chromium（铬）, manganese（锰）, molybdenum（钼）, tungsten（钨）, vanadium（钒）, etc.1. Carbon steels 1) Low carbon steel containing from 0.05 to 0.15 percent carbon, which is also known as machine steel;2) Medium carbon steel containing from 0.15 to 0.06 perce

15、nt carbon;3) High carbon steel containing from 0.06 to 1.50 percent carbon, which is sometimes called “tool steel”.2. Alloy steels 1) Special alloy steel, such as nickel steel, chromium steel;2) High-speed steel also known as self-hardening steel.Carbon steels are the most common steels used in indu

16、stry. The properties of these steels depend only on the percentage of carbon they contain. Low carbon steels are very soft and can be used for bolts and for machine parts that have no strength requirements. Medium carbon steel is a better grade and stronger than low carbon steel. High carbon steel is can be hardened by heating it to a certain temperature and then quickly cooling it in water. The more carbon the steel c