UNIT 3: STRUCTURES, STONES AND CERAMICS
KEY WORDS
1. -FORCES AND STRUCTURES
Act on: have an effect on something. Set: group of elements that belong together. Skyscraper: very tall building with many floors. Tend to: often do something or have the tendency to do something.
1. 1-FORCES There are many different forces in nature: Ø Ø Ø Ø Ø
Gravity The force of the wind Mechanical forces that move machines Pressures of gases in closed containers The force created by our own muscles
Forces act on us and we use forces all the time, but what is a force? How can we define it? A force is anything that can deform a body (static effect) or change its state of movement or rest (dynamic effect)
1. 1-STRUCTURES A structure is the set of elements in a body that are intended to resist the effects of the forces that act on it. A structure prevents a body from breaking or becoming too deformed. All bodies must have a structure that can resist forces- bird´s nest, shell, a tin, a skyscraper, electrical towers, etc. The first two are natural structures that are not made by humans, while the other are artificial, human-made structures. Structures are necessary because all bodies are subjected to the effects of forces that tend to deform them. The forces that act on a structure are called loads
There are two main types of loads, permanent and variable: Ø Ø
Fixed or permanent loads don´t vary over time. They always affect the structure in the same way. For example, the object´s own weight. Variable loads are occasional and changeable. For example the weight of snow on a roof.
Loads act on bodies, causing internal tension, which vary depending on how they´re applied, and the specific shape of the objects. These tensions are called stresses.
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UNIT 3: STRUCTURES, STONES AND CERAMICS
2. -STRESSES When you make a physical effort you may notice that you can feel tension that increases as the effort increases. This internal tension is called stress. It happens to all bodies subjected to the applying of one or more forces on them.
2.1 –MAIN TYPES OF STRESSES Ø
Traction: Forces try to stretch the object they are acting upon. Opposing forces move outwards away from the body along the same trajectory and in opposite directions. The body tends to become longer.
Ø
Bending: Forces try to bend a body. This stress acts on elements that are supported at their extremities and have a weight applied them.
Ø
Compression: Forces try to flatten or compress a body. Opposing forces move inwards towards one another along the same trajectory and in opposite directions.
KEY WORDS Stretch: be made longer or wider. Trajectory: the path followed by a moving object. Bend: form into a curved or angled shape. Flatten: form into a curved or angled shape. Twist: form into a curled shape or turn in opposite directions.
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UNIT 3: STRUCTURES, STONES AND CERAMICS
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Torsion: Forces try to twist a body. The usually try to turn the body in opposite directions.
KEY WORDS Waterproof: doesn´t allow water to enter, impermeable. Gypsum: soft, white, absorbent, mineral rock.
3. - STONES Different types of stone are found in large blocks in the earth. For example, marble, granite and slate. We can also find them in different sized granules and fragments, for example, sand and gravel. Ø
Marble and granite have high density, are hard and are very resistant to environmental conditions.
Ø
Slate is hard, dense and waterproof. It´s used in roofs and paving.
3.1.- STONE BINDERS Sand and gravel are used directly to make asphalt and also for binders, which are used to join other materials together. Ø
Plaster is processed from crushed gypsum that is dehydrated. It´s used to make archways, partitions and as a covering for walls and paving, etc.
Ø
Cement is a grey powder made from a mixture of crushed and heated limestone, clay and gypsum. It´s used to hold together construction materials.
GYPSUM
CEMENT
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Mortar is made from cement and sand that hardens when mixed with water. It´s used to hold together construction materials and to make artificial stone.
Ø
Concrete is a mixture of gravel, sand, water and cement. It´s used to make foundations for buildings, bridges, etc. CONCRETE
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UNIT 3: STRUCTURES, STONES AND CERAMICS
4. - CERAMICS We make ceramics form clay. The process has several stages. We used ceramics to make bricks, tiles, pottery, crockery and so on. There are two large groups: structural ceramics, which are permeable, and whiteware ceramics, that are impermeable. Ø
Whiteware ceramics include stoneware and porcelain.
Ø
Structural ceramics include baked clay, earthware and heat resistant materials.
5. - GLASS Glass is a transparent or translucent material that can have different textures and colours. It´s waterproof, smooth and hard but fragile. It´s resistant to environmental conditions and to chemical elements. It´s good thermal, electrical and acoustic insulator. We make glass by mixing sand, soda and limestone, and then we heat this mixture to very high temperature. We can use different techniques to obtain the required shape.
KEY WORDS Clay: fine earth composed of aluminium silicates and other substances. Translucent: material that light can pass through, but details cannot be distinguished clearly. Soda: common name for sodium hydroxide. Limestone: rock with very high calcium content.
Ø
Mould blowing: we shape the material by injecting air.
Ø
Float glass making: we float glass in liquid form over tin, also in liquid form. The glass forms a sheet and solidifies.
Ø
Lamination: we pass the soft material through a system of rollers. The rollers can be smooth, or engraved to make a design on the glass
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UNIT 3: STRUCTURES, STONES AND CERAMICS
6. -ACTIVITIES 1.
Look at the following photographs, talk to your partner and answer the questions:
a. Are there any animals that build structures? Give examples. b. Which parts of the bodies of living beings from their structure? c. Which of the structures in the pictures are artificial? 2.
Look at the pictures below and answer the questions.
a. What material do we use to make these objects? b. What other everyday objects are made from these materials? 3.
Write five examples of natural structures and five examples of artificial structures.
4.
Which is the easiest way to break a raw piece of spaghetti: stretching it, twisting it or bending it?
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UNIT 3: STRUCTURES, STONES AND CERAMICS
5.
Copy the diagram of the swing in your book and label the stresses each element bears: compression, bending traction, bending, traction and compression.
6.
Which stress would be easiest to use to break the pen? Which would be the most difficult?
7.
Look at the illustration below and answer the questions:
a. What materials are used to make the elements shown? b. Which raw materials do we use to make them?
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