Lesson 3 mechanisms

Task 1. Look at the pictures and identify the mechanisms. Work in pairs and explain the principles on which they operate.

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Task 2. Scan the text and find out which of these mechanisms are mentioned. Discuss with a partner which of these mechanisms are widely used in every day life.

cam foot pump tap escalator pendulum

Mechanisms

Mechanisms are an important part of everyday life. They allow us to do simple things like switch on lights, turn taps, and open doors. They also make it possible to use escalators and lifts, travel in cars, and fly from continent to continent.

Mechanisms play a vital role in industry. While many industrial processes have electronic control systems, it is still mechanisms that deliver the power to do the work. They provide the forces to press steel sheets into car body panels, to lift large components from place to place, to force plastic through dies to make pipes.

All mechanisms involve some kind of motion. The four basic kinds of motion are:

Rotary: Wheels, gears, and rollers involve rotary movement.

Oscillating: The pendulum of a clock oscillates - it swings backwards and forwards.

Linear: The linear movement of a paper trimmer is used to cut the edge of the paper.

Reciprocating: The piston in a combustion engine reciprocates.

Many mechanisms involve changing one kind of motion into another type. For example, the reciprocating motion of a piston is changed 20 into a rotary motion by the crankshaft, while a cam converts the rotary motion of the engine into the reciprocating motion required to operate the valves.

Task 3. Read the text to find the answers to the following questions. Discuss your answers with a partner.

1. What does a cam do?

2. What does oscillating mean?

3. How are plastic pipes formed?

4. What simple mechanisms in the home are mentioned directly or indirectly?

5. What is the function of a crankshaft?

6. Give an example of a device which can produce a linear movement.

7. How are car body panels formed?

8. What do mechanisms provide in industry?

Task 4. You are going to read the text about scissors. Before reading it discuss with a partner what you know about this device. Try to persuade your partner that it is a vital device.

Task 5. Read the text (Source: Encyclopedia Britannica).

Scissors

Scissors is a cutting instrument which consists of a pair of opposed metal blades that meet and cut when the handles at their ends are brought together. The term shears sometimes denotes large-size scissors. Modern instruments are of two types: the more usual pivoted blades have a rivet or screw connection between the cutting ends and the handle ends; spring shears have a C-shaped spring connection at the handle ends.

Spring-type scissors probably date from the Bronze Age and were commonly used in Europe until the end of the Middle Ages. Pivoted scissors of bronze and iron were used in ancient Rome and in China, Japan, and Korea. In Europe their domestic use dates from the 16th century, but not until 1761, when Robert Hinchliffe of Sheffield, England, first used cast steel in their manufacture, did large-scale production begin. In the 19th century much hand-forged work was produced, with elaborately ornamented handles. By the end of the 19th century, styles were simplified for mechanical-production methods.

The two blades are made to twist or curve slightly toward one another so that they touch in only two places: at the pivot, or joint, and at the spot along the blades where the cutting is taking place. When completely closed, the points of the blades touch. In the case of the finest cutting instruments, the two unfinished metal blanks and the fasteners are coded with an identifying mark so they can be manufactured as a set.

Blanks are usually made from red-hot steel bars that are forged at high speed between the dies of drop hammers, but others also of satisfactory quality may be made from cold-forged blanks. The steel may contain from 0.55 to 1.03 percent carbon, the higher carbon content providing a harder cutting steel for certain applications. Stainless steel is used for surgical scissors. Certain nonferrous alloys that will not produce sparks or interfere with magnetism are employed in making scissors for cutting cordite and magnetic tape. Handle and blade are usually constructed in one piece, but in some cases the handles are electrically welded to the steel blades.

Expert sharpening is required to restore the edge-angle sharpness; each blade is passed smoothly and lightly across a grinding wheel, following the twist of the blade, with an even pressure throughout the stroke to avoid causing ridges or other irregularities.

A special form of shears used for sheet-metal work, called tin shears, or tin snips, is equipped with high-leverage handles to facilitate cutting the metal. Another special form, pruning shears, are designed for trimming shrubs and trees.

Task 6. Make up questions to the text beginning with the following words. Ask your partner to answer them.

What Where Why When How much Who

Task 7. Look through the text again and decide what the following numbers refer to. Discuss your ideas with a partner.

16 1761 19 0.55 1.03

Task 8. Summarize the information you have learned about mechanisms and scissors in particular.

Task 9. Watch the video “How Clocks Work” and answer the question – how do clocks work?

Task 10. Prepare a presentation on any mechanism.