Gears or toothed wheels are type drives which are used to transmit motion between two shafts or a shaft and a component having linear motion, by the meshing of two or more gears.

The ratio of the rotational speeds of two meshed gears is called the Gear ratio.

The smaller gear makes more revolutions in a given period of time; it turns faster. We always have:

(Speed gear A * Number of teeth Gear A) = (Speed  gear B * Number of teeth gear B)

Gears exercises
Exercise  1.  What is the output in revolutions per minute at Gear C? .	Exercise 2: Gear A revolves at 90revs/min. What is the output and direction at Gear C.
Exercise 3: Calculate the output speed (the speed at which the blue gear moves) if: V1= 3000 (Orange gear) and t1=20 teeth, T2 = 50 teeth and T3 = 200 teeth
Compounds Gears In a compound gear, all gears are fixed on the same axel moving at the same speed. This is an example of a “compound gear train”. Gear A rotates in a clockwise direction at 30 revs/min. What is the output in revs/min at D and what is the direction of rotation ?

Worm Gear

If you want to create a high gear ratio, nothing beats the worm gear. In a worm gear, a threaded shaft engages the teeth on a gear. Each time the shaft spins one revolution, the gear moves one tooth forward. If the gear has 60 teeth, you have a 60:1 gear ratio in a very small package. Below these words, a worm gear representation and  a windshield wiper.

 

 

 

 

 

 

 

 

 

 

Gear and belt

 

 

 

 

The advantages of chains and belts are their light weight, their ability to separate the two gears by some distance, and their ability to connect many gears together on the same chain or belt. On the right, you can see some toothed belt connecting the axel motor to other components of the car engine

Pulley systems

The figure on the left shows a small driver pulley  pulling round a larger driven pulley. The rpm (revolutions per minute) of the larger driven pulley wheel will be less than the smaller driver pulley wheel.

Notice the shaded areas in both pulleys. In the time the small one makes one turn, the bigger just makes a half turn.

Pulley systems are used when there is a need to transmit rotary motion.. It is a simple mechanical device to winch a rope up and down. When the motor is turned on it turns the driver pulley wheel. The belt causes the driven pulley wheel to rotate as well, winding out the rope.

Gear wheels and chains

Everyone has used a bicycle and noticed that it is driven by a large driver gear wheel (pedal gear) with pedals attached. Smaller gears at the back are driven round, in turn driving round the back wheel. As the back wheel turns the bicycle moves forwards. Gears driven by chains are used in motorcycles, in car engines , etc

Rack and pinion

The rack and pinion gear system allows rotary motion of the steering wheel to be converted to linear motion.

The picture ( below) shows  a vehicle and its steering system. This allows the steering wheel to turn the wheels left and right so that it can be steered.

Crank-connecting rod

A Crank-connecting-rod is a Mechanism for transformation of rectilineal  motion into a rotatory one  and  vice versa

 

 

 

 

 

 

 

 

 

Above, the crankshaft( in red), sometimes casually abbreviated to crank, is the part of an engine which translates reciprocating linear piston motion into rotation

 

Cam and follower system

A cam and follower system is a mechanism that uses a cam ( blue piece) and follower to create a specific motion.  The cam is in most cases merely a flat piece of metal that has a specific shape

Dictionary:

shafts: A long, generally cylindrical, bar that rotates and transmits power, such  as the drive shaft of an engine

Wander: To move about without any particular destination

1º The function of slates is to prevent water from penetrating the roof of houses. They are principally made of clay and they are cooked at a high temperature. What is the name of one of the components which
facilitates the smelting?
a. Thermo-sand
b. Feldspar
c. Alkali
d. Heat-resistant sand

2º Another basic component of house construction is the use of hollow bricks. How are they constructed?
a. Absorption moulding
b.  Compression moulding
c. Extrusion moulding
d. Injection moulding

3º Binding materials, like cement and plaster, are sold in pulverized forms and have a chemical reaction when mixed with water, which harden quickly. This process is called:
a. Crystallization
b. Solidification
c. Cementation
d. Concrete set
4º Answer this question. Is concrete stronger in compression, tension, or the same in either?
5º Circle the possible components of concrete.
cement, iron,  gravel,  sand,  rods, water, air
6º Search on the Internet:->   When was concrete first made ?

a) 1245

b) 1567

c) 5000 BC

d) 500 BC

7º In order to make a concrete column, it is necessary to mix:
a. Water, sand and dirt.
b. Sand, water, gravel and clay.
c. Sand, water, gravel and cement.
d. Cement, clay, dirt and water.

8º In the following images, you can see that they are making a concrete column, for which a iron structure is added. Why is the iron structure added to the concrete mass?

a. To add more resistance to compression
b. So the column lasts many years
c. To increase resistance to traction
d. To support the large weight

9º) Mortar is:
a. A mix of sand, slaked lime and cement.
b. A mix of sand, slaked lime and plaster.
c. A mix of plaster, slaked lime and cement.
d. A mix of sand, water and cement.

10º) In building construction, the total weight falls on elements called:
a. Foundations
b. Weight beams
c. Column base
d. A general structure with beams and tie-beams

11º) Materials are tested in a laboratory before being used. For that, practices are done with 1 to 2 cm2 bars of various materials. Of the following, which would perform best in a compression test?
a. Concrete
b. Steel
c. Glass
d. Iron

12º) It is important to know the density of a material in order to know the total weight of a building. In a skyscraper, the beams and tie-beams are numerous and all of its weight has to be supported by the interior
beams. Calculate the density of a circular steel beam of 41,33 kg with a diameter of 15 cm and length of 30 cm.
a. 7800 Kg./m2
b. 2500 Kg./m2
c. 0,78 Kg./m2
d. 78 Kg./m2

13º) In order to create glass
a. Ferric oxide is added in order to increase its hardness
b. Compression is used
c. Alkali is added for colour
d. Alkali is added for greater crystal stability

14º) In the following image, a blue glass bottle is shown and it has a very particular shape. How do you think it was made?
a. Cobalt oxide is added to the blue color
b. An extra bit of sand is added in order to increase its malleability.

c. It has a low percentage of alkali in order to decrease its stability in the cooling process.
d. A blowing method is used and it cools quickly so the color changes.
15º) In order to create glass, a special machine is used in which various substances are mixed together. In this machine:
a. The sand is heated in order to speed up the process.

b. Sand, alkali, Feldspar and oxides are added and heated in an oven at 3200 C.

c. The oven is set at mild before cutting.

d. The glass is cooled before cutting in order to avoid acridness

 

16º) Which of the following are stone materials?
a) Marble, slate and sand
b) Marble, gravel and plaster.
c) Bricks, glass and cement.
2º. A house:
a) Has exterior walls which support the structure’s weight.
b) Can have a double wall, made of brick, hidden in the interior.
c) Has a waterproof cover made of fiberglass mixed with steel.
17º. Which has less resistance to compression?
a) Glass over steel.
b) Concrete over glass.
c) Steel over concrete.

18º. Which is more resistant to traction?
a) Glass over steel.
b) Steel over concrete.
c) Concrete over glass.

19º Stone materials:
a) Only marble, slate and granite are used in construction.
b) Are used in a compact form, like marble or granite, or in the granulated form, like grains or gravel.
c) Are minerals with different chemical compositions, very resistant, hard, with low thermal conductivity and easy to mold.

20º. Ceramic materials like clay:
a) Are cooked before molded through a heating system.
b) Are molded before being cooking in ovens, with temperatures between 900 and 1200 C.
c) Can be used without cooking, like bricks or tiles which air dry after being made.

21º. Glass:
a) Is a plastic material before completely solidifying, which is when it becomes glass.
b) Becomes glass when it mixes with metallic oxides which give it color and stability.
c) Is a mix of molten sand, alcohol, and metallic oxides, which are dumped over a liquid metal, which floats above it.
22º. Binding materials:
a) React naturally with water, producing a forged reaction which bond particles like sand and gravel.
b) A homogeneous mixture of plaster and cement, which, mixed with water, produce concrete.
c) Act like glue when bonding the cement with the concrete.

23º. When making mortar:
a) It is used when plastering a home.
b) It is a mix of cement, sand and water.
c) It is a mix of cement, water, sand and gravel which help in sticking bricks.

24º. Concrete:
a) Should come prepared in concrete trucks. From there comes the price.
b) Is produced by pouring concrete over a mold which contains tense cables.
c) Has steel bars in its interior, which is known as ferralla

Solutions:

 Ceramics:

All types of bricks used in construction are ceramic materials that are modelled and dried by the action of heat. The most important components of bricks are traditional clays. Clay is a natural product which has decomposed from rock within the earth’s crust for millions and millions of years. In order to get a brick, clay is mixed with additives that give the ceramic brick different properties when fired. An essential element is feldspar: feldspar is the second most important ingredient in making bricks, after clay. The great feature of Feldspar is that it does not have a strict melting point. Appropriate mixing of clay and feldspar allows us to reduce the melting point, as Feldspars are used as fluxing agents. Feldspar improves the toughness, strength, and durability of the ceramic brick.

Glass:

What do we understand by Glass?

All we know is that it is a transparent ,  hard and  brittle solid,  used for many bottles  or windows.

Do not worry, sugar glass doesn’t contain any glass element !

If you’ve ever seen the film Terminator 2 where a actor is thrown through a window – and you’ve wondered “how did they do that?”, Well just sugar and more sugar.

The optical and physical properties of glass make it suitable for construction applications such as flat glass for windows, thermal insulators (glass wool which fills up the space between two walls ) internal glazed partitions, etc

A wide variety of colours may be obtained by addition of dispersed particles, such as soda-lime glass for a colourless glass or iron(II) oxide (FeO) which produce a green shade. To obtain float glass, a combination of metallic oxide ( for colour ), sand and alkali is required.

Reinforced concrete

It is concrete in which reinforcement bars (iron bars ) have been incorporated to strengthen the material. Remember that concrete is good at compression efforts but bad at tension efforts. Iron has a good tension efforts value so adding iron to concrete will lead to a material good at both compression and tension. Concrete has a compressive stresses of about 27.5 MPa, however, any appreciable tension (e.g. due to bending in a beam will break the beam. If steel is placed in concrete, then the reinforced concrete resists compression but also bending. In a beam element there is a tension and a compression force.

Prestressed Reinforced Concrete:

Where the concrete will experience higher tensile stress, such as in a bridge or a beam supporting the roof of a sports stadium, it is necessary to apply tension to the steel reinforcement so as to counteract the high tensile stress applied to the concrete. See next illustration.

From the top to the bottom:

1 st Rebar: a steel reinforcing bar used in concrete. It is usually formed from mild steel, and has a patterned surface for better adhesion to the concrete.

2nd These methods involve stretching the steel reinforcement bars (tendons)  before  the concrete hardens. 3rd In pre-tensioning the steel ¡s anchored at one end and stretched by hydraulic jacks from the other end until the required tension is achieved.  The casting is then usually steam-cured for twenty-four hours to rapidly obtain a typical 28 N/mm2 compressive strength. The steel has a patterned surface, which allows the concrete to achieve a firm bond to it. 4th When the concrete has sufficiently hardened the steel projecting out at each end is cut flush with the end of the beam.

5th Prestressed reinforced concrete is finished and ready to support the load.

 

 

Materials exercises

 

 

Dictionary:

counteract: To oppose and mitigate the effects of a contrary action.

Patterned: a model or form of metal, used for giving the bar an extra adhesion  to the concrete.

Hardens: To make hard or harder

 The different parts of a structure are either in compression or in tension, or both.

A steel cable one centimetre in diameter can support up to 9,000 kg or what is nearly the same, the weight of two  Indian elephants!.

In construction, stone is not a good choice for a tension structure but it is, however, strong under compression. Egyptian pyramids were made of enormous stone blocks, weighing over 1000 kg. The blocks on the bottom support the weight of the upper blocks. Generally speaking, force changes or tries to change the shape or movement of a body. A force can cause a body to accelerate. The actual acceleration of the body depends on the sum of all forces acting on it. Every force acts in a particular direction, but most of the forces can be reduced to a combination of compression and tension.

Forces are measured in newtons.

First of all, a physics concept:

Density:

 It is a measure of the mass of the substance in a standard unit of volume. The  way to find out  the density of a substance is to measure its mass and its volume, then divide the mass by the volume Density = Mass ÷ Volume

Compression.

A pushing force that tries to shorten a structural element. How can you  feel compression?. Just,  put your hands together and push hard.

Examples of structural elements in compression: arch bridges ( see picture on the right), human legs, tree trunks …..

Let’s see  the compression resistance of some materials. The unit used is MPa = Mega Pascal; 1 pascal (Pa) = 1 N/m²

Material	Compression Resistance (MPa)
Concrete	55
Steel	450
Glass	1000

 Tension.

A pulling forces that tries to make a structural element longer. How can you feel Tension?. Link your hands together and pull.

 

Dictionary:

Sliding: to move along in continuous contact with a smooth surface drill bit: These are cutting tools used to create cylindrical holes. Bits are held in a tool called a drill, which rotates them and provides axial force to create the hole Door handle A doorhandle is the device mounted on the exterior and interior of automobile doors for the purpose of opening them

 

1. Structureis comprised of pillars, beams and tie-beams made of reinforced concrete or iron.

The structural system of every house is required to support and transmit various loads. These Loads can be classed as static or dynamic.

In houses, the structural and enclosure systems ( external and internal walls ) are sometimes integrated. For example, the external walls  of a typical 1920 “extremadura” house  serve as both the structural and enclosure system.

Static Loads:

Loads that are applied slowly  to a structure and do not change quickly. Examples of static loads include:

Live  Loads: Any moving or movable loads resulting from people, collected water and/or snow or movable equipment.

 Dead Loads. Loads associated with the building weight and any elements permanently attached  to it

Soil and Hydraulic Loads. Ground pressure loads exerted on a rising wall and hydraulic loads from groundwater

Dynamic Loads.

Loads that are applied suddenly to a structure, often with rapid changes in magnitude and point of application

Wind Loads. Forces exerted by the energy of moving air.

Earthquake Loads- Cause lateral movement at the base of a building that  can cause failure or collapse in extreme cases. Flexible buildings such as timber-frame structure perform well under earthquake loads

1. Floors and ceiling.

The primary functions of the floor are to support the imposed loads and to provide a level surface for the activities that are carried out in the home.

Floors must be designed to meet a number of performance requirements, including:

Strength and stability. Floors experience both dead and live loading throughout the lifetime of the building. The live loads can vary significantly depending on the number of people living in a home and activities occurring there. For example, taking a bath  can increase the load on the bathroom floor by up 150 kg.

Durability. The floors of every house must be hard-wearing if they are to  withstand the demand of everyday use.

Moisture resistance.  Ground floors must be designed to withstand moisture rising from the ground floors. If moisture rises up through the floor, in English houses,  timber floorboards will cup and natural carpets will rot.

Thermal insulator. .Ground floors must protect against the loss of heat through the floor. Generally, we think of heat as rising, however, all you have to do is to lie down on the ground during cold weather to realise how it draws heat out of you body. Uninsulated or poorly insulated floors will lead to cold homes and higher heating costs.

A typical Spanish Home uses hollow tiles to withstand both live and dead loads. Made of clay or concrete, they are placed between two tie-beams. It is very easy to install as you only have to put it between two tie-beams. Later, cover with a concrete layer which could contain a iron wire netting (see next illustration).

 

 

The hollow tile is later coved by a layer of concrete. Floors are finished with floor tiles or boards.

Exteriors walls

The primary functions of the external walls of a house are to support the loads generated  ( only in case of a no-columns structure )  and to create a comfortable living space. Walls   must be designed to meet a number of performance requirements including: 1st Strength and Stability — The strength and stability of an external wall depends on: — the strength of the components used (E.g. blocks, mortar)

— Slenderness Ratio — tall, thin walls are less stable than short, thick walls

— Eccentricity of the applied load — the force experienced by the wall from above must be centred.

Bonding is an essential design feature of masonry walls and greatly improves the strength of a wall by ensuring that it performs as a continual unit. Bonding is defined as the overlapping of blocks or bricks to ensure that the vertical and lateral loads are dispersed evenly throughout the wall. See photo below

2º Weather Resistance — Designing for weather resistance is mainly about preventing the penetration of  wind-driven rain.

The most t common method used for housing is the cavity construction. This  involves building a wall that consists of two separate walls, an inner wall  and an  outer wall, with a small gap ( called a cavity ) between them and another bigger gap for an  insulator. The cavity prevents the moisture absorbed by the outer wall reaching the insulator and the inner wall. The inner and outer walls used in  construction are normally referred to as the inner leaf and the outer leaf.

The function of the outer leaf is to protect the inner leaf from the effects of weathering. The function of the inner leaf is to support the loads of the house ( Only in traditional houses. Nowadays, in modern houses and buildings, the columns support the loads ).

3 rd Thermal Insulator.  The proper thermal insulation of walls is  essential to ensure that heat is not lost from the home. Poor thermal insulation leads to greater fuel use which in turn is damaging to the environment and expensive for the home owner. Masonry cavity walls are usually insulated by placing a continuous layer of rigid expanded polystyrene foam insulator into the cavity. This insulation board is held tightly against the  inner leaf. This means that when the house is heated the heat energy is absorbed by the inner leaf. For this reason it can take some time for a comfortable temperature to be achieved.  However, once warm, concrete cavity-walled homes can remain so for several  hours after the heating is turned off, as the concrete inner leaf acts as a heat store.

Windows:

The primary functions of a window are to admit light and fresh air into a building. Light and fresh air are essential to a healthy space. The big problem of window is the loss of heat. The greater the window’s surface the more money you have to pay. So a proper thermal insulation design is very important. Poorly insulated, draughty windows are uncomfortable to sit near and waste heat energy. The thermal insulation of windows is achieved primarily through the use of double-glazing and weather stripping. Double-glazing is designed to reduce the amount of heat lost through the glass, while weather stripping is designed to reduce the amount of heat lost due to air infiltration (draughts). Double-glazing can significantly reduce the amount of heat lost through a typical window.

In the photo above this paragraph, a further improvement can be made by  applying a special Low-emissivity (Low-e) coating to the inner pane of glass. Low-e glazing allows the short-wavelength heat energy from the sun to enter the house but acts as a barrier to the escape of the Long-wavelength energy from internal heat sources. About 60% of the heat energy lost between the panes of glass in a double-glazed window is long-wave radiation.

Roofs:

The primary functions of a roof are to protect a building from the weather and to retain the heat generated inside. Roofs must be designed to meet a number of performance requirements, including:

1st Strength and Stability — The structural stability of a roof is tested every day. The Loads exerted by the weight of roof tiles, the wind blowing against it and the additional weight of rain or snow, are considerable. • Weather Resistance — Every roof in the world is sloped to some extent. Even so-called flat roofs are slightly sloped. The reason we slope roofs is to dispel rainwater. • Thermal Insulation — To prevent heat loss the attic space of most roofs ¡s insulated with blanket (quilted) insulation.

Internal walls

The primary functions of internal walls is to divide the overall space within the house into smaller spaces. The Next photo shows the electrical circuit and plumbing.

Dictionary:

Failure: an act or instance of failing or proving unsuccessful; lack of success.

Moisture: wetness caused by water

Rot: to deteriorate, disintegrate, fall, or become weak due to decay

Slenderness: thin or slight

Masonry:  work constructed by a mason, stonework or brickwork

Mason: a person whose trade is building with units of various construction  products, such as stones, bricks, or tiles, usually with the use of mortar or cement as a bonding agent.

The illustration shown on the right represents the essential  elements of a modern Building.

Parts:

1. Foundations: This is a structure ( made, mainly, of cement, iron and  gravel ) that transfers loads to the earth. The primary design concerns are settlement and bearing capacity
2. Structure: This is comprised of pillars, beams and tie-beams made of reinforced concrete or iron
3. Floors and ceiling: Hollow tile are placed between two tie-beams, later it is covered by a layer of concrete. Floors are finished with floor tiles or floorboard.
4. Exteriors walls: These are usually made by two  brick walls  and an insulator layer ( to avoid the  heat loss).
5. Windows: These  provide a visual link between internal space and  the outside world. They are very important to the mental health of the people in the house. A small tie-beam is placed above the window to  bear the load of all bricks situated over the window frame.
6. Roof. Its functions are to protect a building from the weather and to retain the heat generated inside. It is  comprised of a wood or iron  structure, a thermal material such as fiberglass  and the last layer, the tiles or slates.
7.  Internal walls. The primary function of internal wall is to divide the overall space within the house into smaller spaces. They are made of brick, wood or plaster.

Each of every part in the building has its own functions and a good  design is crucial.

Foundations. Soils:

Most people would agree that walking in sand is harder than walking on a concrete footpath. This is because your feet tend to sink into the sand when you try to move forward. A similar thing happens when a house is built — it sinks into the ground. Of course, the extent to which a house sinks into the soil is so small that it isn’t noticeable. This is because investigations are carried out to ensure that the ground is strong enough to support the weight of the building before construction begins. This is done by checking what type of soil is below ground level. Some soils are good at supporting loads, others are not. By establishing the soil type and comparing it to known performance figures, the designer can be confident that the building will not sink when complete.

Foundations:

A foundation is the part of a structure that transfers the loads from the structure to the ground. It is essential that the loads are spread safely and evenly over the supporting ground to ensure the stability of the building. In most cases we do not see the foundation of a building because it is below ground level.

As well as supporting the weight of the building, the foundation provides a level bed on which to build. While we usually think in terms of the building´s weight keeping it in place, in some cases, especially for taller buildings, the foundation actually anchors the building to the ground. A properly designed foundation will limit settlement, ¡.e. the tendency for a new building to sink into the ground. It is normal for a building to experience some settlement. This is because most soils are a mixture of the soil, air and water. When the building load is exerted on the soil, the air and water are driven out and the soil consolidates. In non-cohesive soils this happens during the construction phase, although in cohesive soils (e.g. clay) it can occur over a period of years. .

Foundations differential settlement will occur if an area of softer soil is undetected. ( See image above on the left ). Above on the right, a properly designed foundation will safely and evenly transmit the load over the supporting ground to ensure the stability of the building. Now, there is not cracking in the house frontage.

The function of a foundation can be summarised as follow:

To transmit all building load to the ground

To limit settlement and prevent subsidence

to provide a level bed on which to build

to anchor the structure to the ground

 

A foundation is always wider than the element (e.g. wall or column) which it is supporting. This is so that the load ¡s spread over a greater area. The bearing pressure exerted on the soil by a structure is the force per unit of area. For example,  if it the bearing pressure is 100 kN/m2 this could be 10 kN exerted on 10 m2 or 5 kN exerted on 20 m2. Therefore, as the area increases the force exerted decreases. By increasing the area of a foundation under a house, the force exerted per square metre on the soil is decreased. For this reason, a traditional strip foundation (commonly used for house construction) is always three times wider than the overall width of the wall. In this illustration a structure without foundations will sink. A tree times wider foundation will support all load without movement.

 

Strip foundation: the lower portion of the strip is stretched (tension) as the foundation bends under loading. Placing steel reinforcement in the foundation counteracts this and ensures the foundation remains stable.

Dictionary:

Consolidation: When stress is applied to a soil that causes the soil particles to pack together more tightly, therefore reducing its  volume. Process by which soils decrease in volume.

Gravel: small stones and pebbles (very  small, rounded stone), or a mixture of these with sand Bearing Capacity: is the capacity of soil to support the loads applied to the ground.

Hollow tile: A hollow building block of concrete or Terra cotta   used for making  exterior walls,   floors or roofs. Also known as hollow block Concrete: is a construction material composed of cement, sand, water  as well as other cement like materials.

Tiles: a thin slab or bent piece of baked clay, sometimes painted or glazed, used for various purposes, such as to form one of the units of a roof covering or floor (other shape )

Slates:  1. A piece of this rock cut for use as roofing. 2. A writing tablet made of a similar material. Plaster: a composition, such as one made of lime or gypsum and sand and water, applied in a pasty form to walls, ceilings, etc.

Settlement: is defined as downward movement of the soil, or any structure on it, as a result of soil consolidation, usually caused by the load applied by the structure.

Clay: a natural earthy material that is plastic when wet, consisting essentially of hydrated silicates of aluminum: used for making bricks, pottery, etc

Millions of years ago, man used to manage simples materials, such as wood, to make unsophisticated tools or constructions Nowadays, man has invented new materials which can be used in many different situations, even in our own bodies ( See illustration on the right where old tooth are replaced by implants.

Materials and Components

1. Choosing the correct material for any particular task is essential for a manufacturing activity. Materials can be natural or artificial. Natural resources are split into 3 categories. 1. Animal 2. Vegetable 3. Mineral

Artificial Materials: ARE THOSE WHICH HAVE BEEN MADE BY MAN

TYPES OF MATERIALS

1º Wood: Divided into two major classifications: Hardwoods and Softwoods. 2º Metals. There are two significant groups of metals: Ferrous metals, which contain iron and non-ferrous metals, which do not contain iron. Examples of Non-ferrous metals are: Aluminium, Copper, Gold, Silver …

Materials Properties of Materials

Properties of materials can be divided into physical, chemical and ecological

Physical Properties

Electrical Conductivity is  when electricity can run though the material.  Examples: Steel is a good conductor Wood isn’t a good conductor

Optical properties

How materials behave when light touches them. They can be classified into: a) Opaque: No light travels through them. e.g wood b) Transparent: All light travels through them and you can see what’s behind the materials. e.g glass in a  window c) Translucent: All light can travel through them but you cannot see what’s behind them e.g frosted glassSee examples on page 75

What is a thermal conductor and what is an insulator ?

It is the ability of the material to conduct heat. e.g. In a saucepan there is a metal body for thermal conductivity and plastic handles for thermal insulation. Thermal Insulation = It is a bad thermal conductor

Thermal properties

Dilation: When material expands ( gets bigger ) due to heat Contraction: When material gets smaller due to heat.

To think about: Why are rails separated by a gap?

Thermal properties

Fusibility is the ability of a material to change into a liquid when heated to its melting point. Examples of melting points: Iron’s melting point………..1535 ºC

Copper’s melting point……….1083 ºC

Sound Properties

The ability of materials to conduct sound. To think about. Can you speak on the moon. I mean, can your partner hear what you say?. Write some examples of good and bad conductors

Oxidation.

The change that occurs to most metals when in contact with air or/and water

Ecological Properties

Recyclable. Materials that can be reused

Toxic. Materials which are harmful to the environment

Biodegradable. Materials that decompose naturally with time. Examples:An apple takes about 20 days to decompose,  plastic takes about 100 years  and glass takes about 400 years

 

The mouse is a pointing device generally made of plastic.

It is used by one of the hands of the computer user and it detects this hand’s movement in two dimensions on the level surface the mouse is on.

This movement is then reflected on the screen with an arrow or pointer.

It can work on almost any surface. It has a small red diode than bounces the light from a surface onto a CMOS sensor (complimentary metal-oxide semiconductor). The CMOS sensor sends every image to a DSP processor (Digital Signal Processor) to be analysed. The DSP, operating at 18MIPS (millions of instructiosn per second) can detect forms in these images and can see how these forms have moved between images. Based on the changes seen in a sequence of images the DSP works out how the mouse has moved and it sends the corresponding coordinates to the computer.

Printers

 

Printers are peripherals that allow us to print text and images from a digital archive.
The quality of a printer depends on:
The resolution or number of dots an inch that the machines prints.
The speed of the printing that is measured in pages per minute.
Printers are normally connected to the USB port.

Types of printer

Inkjet printer. These printers print using one or various ink cartridges that contain between 3 and 30 ml. Some print in very high quality, almost as good a quality as the Laser printers. See photo on the left.

Laser Printer.

These are the best quality printers and their prices vary widely, depending on the model.I They are the method of printing used in printing presses and they work in a similar way to photocopiers.
The quality of the printing and the speed of laser printers is really surprising.
Plotter. These printers are specialized in vector drawings and very common in architects  studios. See photo on the left.

 

Scanner

 

This is the process used to copy a document:

Light up the image with a spotlight. The light reflected off the object is directed, using mirrors, to the CCD device, which converts it into electronic signals. Then these signals are converted to a digital format thanks to a analog-digital converter that transmits the subsequent flow of bits to the computer.

The CCD is the most important element of a scanner. it is an electrical component that reacts to light. It transmits more or less electricity depending on the intensity and colour of the light.

It’s like an electronic eye and it is also used in other devices, like cameras and videos. The quality of the scanning depends on the refinement of the CCD; the analog-digital converter and adequate cleaning.

 

 

Software

The software is the programmes, like the operating system, the text processors, video games, internet navigators etc.
The best way to learn is to practise with them. We will practise with OpenOffice.
 

 

 

 

 

 

Read and complete:

Voltage and current

A battery is a source of electrical energy – it provides the ‘pressure’ which causes electricity to flow. We measure this electrical pressure in volts, V. The higher the voltage, the greater the pressure.
The flow of electricity is called current and is measured in amps, A.
If a single battery makes a bulb glow dimly, two batteries connected in series as in circuit bellow will make it glow brighter. In the next circuit, 4 batteries are connected in series so the total tension will be  V1 + V2 + V3 + V4.

 

This happens because when batteries are connected in series their voltages ‘add up’. Four similar batteries connected in series ( circuit 2 )   produce  4 times the electrical pressure.

The greater the electrical pressure (in a given circuit) the higher the current.

When batteries are connected in parallel however, their voltages do not ‘add up’. The voltage provided by the two batteries  in circuit 3 is the same as by the single battery in circuit 1.
Even so, there are reasons for connecting batteries in parallel: two batteries last longer than one, and can supply a higher current, should it be required.

Read 3 or 4 times. Later,  do this  exercise

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Calculate the equivalent resistor and the current in the battery.

Remember: In a series circuit, the total resistance of the circuit (also called effective resistance) is equal to the sum of the individual resistances, so Re = R1 + R2 + R3 …

In a parallel circuit, a quicker method of finding  the equivalent resistance is to use the general formula:

1 / Re = 1/R1 + 1/R2  + 1/R3 …..
Solution: Re = 20 Ω  I = 250 mA

Re =   64,18 Ω    I = 77,9 mA

Re = 58,41 Ω     I = 85,6 mA

 

 

1º In this circuit, the value of the battery is 10 Volts and the current measured in the ammeter is 2 mA.

a)  Calculate the value of Resistor 1 in this  circuit.
b)  How much current would flow if the value of  R was doubled?

Solutions: R  = 5 KΩ   and b) I = 1 mA

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2º Calculate the current flowing in this circuit.

b) What would be the ammeter reading if the resistor’s value was halved?

Solutions: a) 200 mA  b) 400 mA

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3º  a) Calculate the current flowing through  the 40 Ohms  resistor.
b) Calculate the current flowing through  the 60 Ohms  resistor.

c) What will be the reading on the  current in the battery?
d ) What is the total resistance in this circuit?
Solutions: V1 = 6 volts b) V2 = 9 volts c) 150 mA d) Rt = 100 Ω

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4º What will be the value of the current flowing through the 100 Ohm resistor?

And what about the current in the other resistor?

Solutions: 50 mA  and 100 mA

 

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6º We have a two parallel resistors. Calculate the total resistance of the circuit and the current flowing through each resister.

Solutions: Rt = 33,33 Ω, I1 = 0,05 A   and I2 = 0,1 A

 

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7º A series circuit has 4 resistances of 20, 40, 10 and 5 Ohms. Calculate the Total resistance and the current flowing through each one if the battery has a value of 10 Volts

Solutions: Total resistance = 75 Ω.  I = 0,13 Amps

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8º In this circuit, calculate:

a )  The total resistance in the circuit

b) The  current flowing in the circuit.

c) The voltage across  every resistor

Solutions:

a) = 40 Ω  b) = 0,225 A   c ) V1 = 2,25  V2 =1,125  V3 = 5,625

Note: If you ad V1 plus V2 plus V3, you get the Battery voltage

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9º  5 ,10 and 25 Ohms resistors are connected in parallel. Calculate the  total resistance and the current flowing through each one

Solutions: Rt = 2,94 Ω  I1 = 1,8 A  I2 = 0,9 A  and I3 = 0,36 A

 

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10º In the circuit on the left, we have 3 series resistors. We measure 8 volts in the voltmeter ( represented by V ).

Calculate the voltage across the 20 Ω  resistance

V = 32 V

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11º  In the next circuit , calculate the voltage across the 20 Ohm resistor.

Solution: 1,64 volts

 

 

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12º What is The electric power?. How it is measured?

13º A hair dryer has a resistance of 100 Ω and it is plugged to a 220 mains supply. If it is  operating for 40 minutes, calculate how many kilowatts per hour of energy does it use and how much do you pay if 1kwh = 0,20€.

14º  What resistor values are indicated by the following colour bands? (A) Blue, black, yellow

15º The atom

16º Conductors and Insulators. Examples

17º Types of currents

18º Define Resistance, Current and voltage.

19ª Ohm law