MOVING PARTS PROFESSIONAL ENGLISH IN USE FOR ENGINEERING

 

PROFESSIONAL ENGLISH IN USE FOR ENGINEERING UNIT 34. MOVING PARTS

 

A Angular motion If a spanner is used to tighten a bolt, one and remains in the same position on the bolt, while the other end turns. This type of motion, where one end of a component pivots while the other end follows the arc of a circle, is called angular motion. An example is a flap on an aircraft wing, which can be moved to different positions. This point at the centre of angular motion is called the axis of rotation (or axis). We say that the motion occurs about the axis (around it).   B Rotary and reciprocating motion When angular is through 360 degrees, it is called a revolution (or rotation). When moving parts of machines, such as wheels, turn through complete revolutions – once, several times, or for continuous periods – we say the revolve (or rotate). The rotational velocity of revolving parts, or rotating parts, is measured in revolutions per minute (rpm) – often called revs per minute. The motion of revolving parts is called rotary motion. C Engine revs The abbreviation for revolution – rev – is widely used to talk about engines. For example: ·      The rotational velocity of an engine is measured by a rev counter. ·      High and low engine speeds are described as high revs and low revs. D Friction Moving parts cause friction. Friction is the force of resistance when two surfaces slide against each other. Frictional resistance is measured as the coefficient of friction. This is the force required to overcome friction in order to allow an object made of a specific material to slide along the surface of another specific material. EXERCISES 34.1 Match the descriptions 91-6) to the terms (a-f). look at A and B opposite to help you. 1. the speed of movement of a part which turns around a point 2. pressure, exerted in an outward direction, due to rotary motion 3. the rate of increase of speed of a part which turns around a point 34.2 Complete the sentences using suitable forms of the words revolve or rotate. Sometimes forms of both words are possible. Look at B opposite to help you. The first one has been done for you. 1. The measurement of _____rotational_____ velocity is rpm. 2. As you can see, the wheel ____________ at extremely high velocity. 3. A recording device counts each ____________ of the wheel. 34.3 Complete the description of an engine problem using words from C opposite. Normally, the engine shouldn’t be able to run faster than the maximum (1) ___________ ____________ at 8,000 rpm. The (2) ___________ ____________ should prevent it from exceeding that limit. But 34.4 Find expressions in D opposite with the following meanings. 1. the measurement of friction 2. the frictional resistance between surfaces that are already sliding against each other 3. the frictional resistance between surfaces that are not yet sliding against each other

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