9. Choose one of the metals mentioned in the text. Think of seven interesting ways it could be used nowadays. Write a short paragraph (60-80 words) about it.
GRAMMAR IN USE
These tasks can help you to practice Present Simple Passive. Read grammar rules on p. 170 - 173 and then do the exercises.
10. Transform sentences from Active into Passive Voice.
People develop different methods.
Metals can conduct heat and electricity.
They can draw an ounce of gold into a wire.
People use bronze for objects intended to resist the corrosive action of the atmosphere.
You can bend elastic materials.
People know zinc as one of the constituents of the alloy brass.
We call bronze an important material in the scientific and technical progress.
11. Complete the sentences, as in the example.
1. It is thought that the college has good teachers.
The college is thought to have good teachers.
2. It is known that people use metals.
People ………………………………………...
3. It is reported that our students work hard.
Our students ……………………………….....
4. It is said that she speaks seven languages.
She …………………………………………….
5. It is said that he is a talented scientist.
He ……………………………………………..
6. It is said that our university team trains for eight hours every day
Our university team ……………………………
7. It is reported that the world leaders discuss different problems.
The world leaders ………………………………
12. In the following description of how plastics are shaped, put the verbs in brackets in the correct form.
Injection moulding Blow moulding Extrusion
There are many ways of shaping plastics. The most common way is by moulding. Blow-moulding (a) ….. (to use) to make bottles. In this process, air (b) ….. (to blow) into a blob of molten plastic inside a hollow mould and the plastic (c) ….. (to force) against the sides of the mould.
Toys and bowls (d) ….. (to make) by injection moulding. Thermoplastic chips (e) ….. first ….. (to heat) until they melt and then forced into a water-cooled mould under pressure. This method (f) ….. (to suit) to mass production. Laminating (g) ….. (to produce) the heat-proof laminate which (h) ….. (to use), for example, for work surfaces in kitchens. In this process a kind of sandwich (i) ….. (to make) of layers of paper or cloth which (j) ….. (to soak) in resin solution. They (k) ….. then ….. (to squeeze) together in a heated press.
Thermoplastics can (l) ….. (to shape) by extrusion. Molten plastic (m) ….. (force) through a shaped hole or die. Fibres for textiles and sheet plastic may (n) ….. (make) by extrusion.
Unit 12
LEAD-IN
Look at the objects in the pictures. What materials do you think they are made of and why?
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In pairs, discuss what is meant by mechanical properties. What mechanical properties do you know?
READING
Read the text and answer the questions that follow. Mechanical Properties
Mechanical properties are those associated with how a material reacts when subjected to external forces. Force will cause material to become stressed. Stress relates to how much load is applied to a given area. Strain is another result of the application of force. This is defined as the amount of distortion (extension or compression) that takes place per unit of length.
Strength is the ability of a material to withstand force without breaking or permanently bending.
Elasticity is the ability of a material to bent and flex when subjected to a force and then to return to its previous form when the force is removed. Structures such as bridges and tall building must have a degree of elasticity.
Plasticity is the ability of a material to be changed permanently in shape (deformed) by the application of an external force without breaking or fractures. Most materials become more plastic when heated. The extent to which a material's shape can become changed by hammering, rolling or pressing is called malleability. Another associated term is ductility; this is the ability to undergo cold plastic deformation by bending or stretching. All ductile materials are malleable, but all malleable materials are not necessarily ductile.
Hardness is the ability to resist abrasive wear, indentation and deformation. This is the important property of cutting tools such as turning tools, drills, files and saws.
Toughness is the ability to withstand sudden stress in the form of shocks or blows without fracturing, and also to resist cracking when subjected to bending forces. Repeated bending will cause the toughness of some materials to break down such that they will eventually fracture.
Brittleness is the opposite of toughness. A brittle material will not withstand shocks or bending without fracture.
Durability is the ability to withstand wear, tear and deterioration with time. Durability refers to both the mechanical properties and the appearance of the surface, particularly of metals, is corrosion. Plastic materials are generally less prone to corrosive effects and are therefore durable.
Stability is the ability to resist changes in shape and size over time. Wood is particularly unstable and tends to warp and twist with changes in humidity. Metals and some plastics tend to gradually deform when subjected to stress over long periods; this process is known as creep.
1. What are mechanical properties?
2. What mechanical properties do you know?
3. What is plasticity?
4. What brittle materials do you know?
5. What is the difference between the durability and the stability?
LANGUAGE DEVELOPMENT