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INTRO TECHNOLOGY BOOK 1
Chapters
Contents
5. Energy
6. Drills
7. Introduction to electricity and magnetism
8. Relationship between electricity and electricity
10. Food
11. Drawing equipment and materials
12. Machines
14. Frictional force
15. Angles
History has taught us that the
ancient man lived in the caves , cloth himself with
the animal skin and depended on bush – hunting produce for himself and his
family alone.
Today , by reason of technology the
modern man can live in decent houses,
cultivate larger quantity of food that can feed more than himself and family.
He is no longer limited to where he
could walk to but could travel far and wide with the aid of aeroplane,
cars and
spaceships. He can monitor world activites through the
Electronic gadgets like t.v, computer, radio, telephones e.t.c
We
can now define technology as systematic knowledge and action usually a indusrial process
but , applicable to any recurrent activity or
practical task technology can also be defined as the use of scientific
knowledge to devlop and produce goods and services
use full to man. Technologists use the discovery of science to produce tools
machines and methods for industry, communication transportation
, machine warfare , food processing conversion of energy into useable
forms e.t.c. In turn, the products of technology are often used by scientists
to further their investigations.
Wood is divided into two; hard and
soft wood.
Hardwood are gotten from deciduous timber trees.
The trees have broad leaves, the seeds are endorsed in a case, the trees shed
their leaves once in a year and grow in the warmer climate ,
the temprate and tropic region.
Soft wood are gotten from coniferous timber trees.
The trees have naked seeds , the don’t shed their
leaves and grow in the cold region of the world from the artic circle down to
about the 50th parallel of latitude.
2.1
CONVERSION
Conversion is the process of splitting of log in the marketable sizes the two popular methods of conversions are: plain sawn and quarter sawn.
2.2 SEASONING
Seasoning
is the process of reducing the water content in wood.The
water log is sometimes referred to sap or moisture.
The reasons for seasoning:-
1. It makes wood stable.
2. It makes wood lighter
3. It makes wood durable
4. It makes wood stronger
5. It makes wood takes paint, polish
e.t.c easily.
6. It makes wood takes preservatives
easily.
To
find moisture content of a given log or timber the following method is put in
to use:-
M.c
= w.l – d.l
x 100
d.l 1
where m.c = moisture contant
w.l = wet log
d.l
= dry log
Example, if a given log or timber weighted
60kg before seasoning and 40kg after seasoning .find the moisture content of
the log?
m.c == 60-40 x 100
40 1
20 x
100
40
1
= 50%
There are two methods of seasoning
woods, these are:-
(a)
Klin seasoning (artificial method)
(b) Air seasoning (natural method)
2.3 DEFECT IN TIMBER
A defect is any feature that reduce the quality and market value timber, such defect are-
a. Shakes
b. Knot
c. Thunder
shake
d. Warpping ---------(Bow and Cup warpping)
e. Pitch
pocket
f. Checks
g. Diagonal
grain.
2.4 VENEERS
Log is softened by steaming and
placed between centers. I t is then slowly rotated whilst a strong knife is fed
into the log and thus
a continous sheet of veneer is peeled off. As the
sheet of veneer
leaves the log, it is cut to size and then passed through a drying machine.
Most plywood is made from rotary cut veneers.
Plywood is made of a number of
(laminations) which are glued together.
2.5 BOARD
Lamin board- is made up of thin strips of
wood glued together and faced with one or more veneer. The strips of wood are
more than 12.5mm wide. It is thus superior to block board and batter board.
Block board- is of similar
construction to lamin board but the strips of wood
are more than 12.5mm wide. When strps of wooare more than
25.5mm wide it is called batter board.
Block board- This is obtain able from 12.5mm thick upwards. It is used for making
flush doors, furniture and large joinery.
3.0
INTRODUCTION TO METAL WOOK
Iron is an element, a basic substance of the earth’s covering. It is found combined with other elements in the form of iron ore.
Iron ore is found in various parts of the world. There are three main type:-
a. HEMITITE.
b. MAGNITITE.
c. LIMONITE
It is mined and conveyed to ironwork.
At the iron works the ores are mixed
with coke and limestone. The coke serves as fuel and the limestone serves as
flux, for the removal of impurities.
Ferrous metal is that contains iron. A non-ferrous metal contains no iron. Example of these metals are:
FERROUS
METAL NON FERROUS METALS
i. CAST IRON
COPPER
ii. WROUGHT IRON LEAD
iii. MILD STEEL ALUMINIUM
TIN
ZINC
BRASS
e.t.c
While, alloy metal
is the mixture of two or more different types of metal. The main purpose of alloying steel
rust but, when chromium and nickel are added to makes stainless steel, this
alloy becomes resistant to rust.
With the exception of a few inert
metals like silver and gold, that occur naturally as pure
metals, all other metals are present in the form of ores. a metal ore is a chemical combination of the metal and some
other impurities in the ore is called Extraction
Extraction of iron is by using a
device called blast furnace. Iron ore, Lime stone and coke are fed into the
device. Blast of hot air is also blown into the furnace through some pipes
called tuyeres. This cause burning
of coke. The heat produced from burning coke melts the iron ore
and limestone. This is followed by chemical reaction that produce molten
(melted) iron and a by-product called slag (also molten) which floats on top of
denser iron.
Smelting is the process of heating a
metallic ore to melting point separating the metal from impurities in ore.
Their on produced by smelting of iron ore in the blast furnace is called pig
iron. It contains some impurities like carbon and sulphur.
3.1 COMPOSITION OF METALS
1. Steel : - is the
name given to almost pure iron. It is an alloy of iron and carbon. Steel is
classified by the amount of carbon it contains:
a. Mild steel - Between o.155and 0.35 carbon.
b. Medium carbon steel - Between0.3% and 0.85carbon.
c. High carbon steel - Between 0.85 and 1.5%carbon.
2. High speed steel:-18% tungsten, 4%
chromium (to give increased hardness and grain) and 1% vanadium (to give increased
toughness)
3. Brass:-
is an alloy of copper and zinc. The amount of copper varied to obtain special
qualities. It is easily worked with hand tools and if containing over 65%
copper is ductile and can be bent cold, but will fracture if bent hot.
Brass has corrosive resisting
qualities and is therefore very suitable for taps, valves, pipes, scaewd and castings.
4. Gliding metals is an alloy of 90%
copper and 10% zinc. It has similar characteristics to copper, but has a lower
melting point. Used mainly for making bowls, jugs, ashtrays, and jewelries.
5. Copper: is obtained from on ore called
PYRITES.
6. Duralumin: is an alloy of 4.5% copper, 0.5% manganese, 0.5% magnesium
and the remainder aluminium.
3.2 PROPERTIES
OF METAL
a. Density: - The weight of an object.
b. Lustre : - Shine or luminosity.
c. Fusibility:-
The property of metal which enables it to liquefy easily.
d. Magnetic:- The property of metal which enable it to
attract iron.
e. Elasticity:- When a metal can be bent and twist easily, it is said to posses elasticity.
f. Hardness: - Resistance being darted.
g. Malleability:- The ability of metal to be rolled, hammered
and bent without cracking.
h. Ductility The
property possessed by metal when it can draw out or stretched without cracking.
i. Toughness When a metal can resist bending,
breaking or stretching, that metal can be said to possessed toughness.
ASS. FOR EVALUATION
1. State all defects in timber?
2. Define technology?
3. State the three types of iron ore?
4. What is an alloy?
5. What is smelting in metal work?
6. What is the composition of the
following metals:
a.
Steel
b.
Brass
c. Gliding metal
d. Copper
Toughness and Ductility in metal
means what?
SOLUTION
1. *
Shakes
* Knot
* Thunder shake
Bow warping
* Warping
Cup warping
* Pitch pocket
* Checks
* Diagonal grain
2. a) Technology is defined as the
systematic knowledge and action usually of industrial process but applicable to
any re current activity or practicable task.
b) Technology can also be define as the use of scientific knowledge to develop and
produce goods and services useful to man.
3. * Limonite
* Magnetite
* Hematite
4. An alloy is the mixture of two or
more miters
5. Smelting is the process of heating a
metallic ore to melting point and separating the metal from impurities in ore.
6. * Steel - iron
and Carbon
* Brass - Copper
and Zink
* Gilding Metal - 90%
Copper and 10% Zink
* Copper - Pynites
7. Toughness: - When a copper can resist bending, Stretching, the is said to be tough
8. Ductility: - The property possessed by metals when it can drawn or stretched without cracking
4.0 PLASTIC
AND CYRAMIC
Metals can be Bert defined any thing
that as weight, can be touch, seen, occupy space and use for various
construction works.
The major groups of material in
technology are:
* Plastic
* Ceramics
* Wood Non- metallic materials.
* Glass
e.t.c
* Metallic materials
Clay
is a material which exist naturally in many part of
the world. When it is wet it can easily be moulded into different
shapes and sizes.
What
ever is constructed with clay, mud cement is called ceramics.
Plastics means that which can shape or moulded when
it is subjected to heat. However, plastic and ceramics have many different
characteristics that make it necessary for us to separate them.
1. While moist, clay or mud can be
moulded or shaped at low temperature, plastics are
moulded or shaped at very high temperature.
2. Although plastics are non –
metallic like ceramics, they are derived from organic materials obtained from
petroleum.
3. Plastics do not break easily like
ceramics however; they are not as strong as metal.
4. Plastics are much higher than
metal and ceramics.
There are two types of plastics: -
a. Thermoplastics
b. Themosets
Those plastics which when heated they
become soft and begin to flow like a liquid again are called thermoplastics.
Themosets are plastic materials,
which we cannot soften it to liquid form by heating. An example is the button
of your shirt. If you put a button in to the fire it gets burnt but does not
change in to liquid.
Energy is the ability to do work. Work
is said to be done when a force mores in the direction of the force. Energy and
work have the same unit as or called joule (j).
The principle of conservation of
energy states that energy can neither be converted from one form to another.
Forms of Energy:-
These are various form of energy,
these are:
Electrical energy.
Mechanical energy.
Chemical energy.
Heat energy.
Light energy.
Nuclear energy.
Sound energy.
Solar energy.
N.B
5.1 MECHANICAL
ENEGY: -
This can be sub – divided
in to two major forms: -
(a)
Kinetic
energy
(b)
Potential
energy
Kinetic energy is the
energy possessed by a moving object e.g. object that
posse the kinetic energy are those that can be change their position: motor
car, aeroplane e.t.c.
The potential energy is the
energy possess by a body at static position.
When a stone was thrown
up it possessed potential energy at maximum light, as soon as it begins to fall
back, the potential energy is converted to kinetic energy.
5.2
CHEMICAL ENERGY: -
This is the energy stored
in the molecules of substance. A fuel is any substance that borne to produce
heat. Examples are petrol and kerosene. This burn in air as a result of burning
the chemical energy started in this converted to heat. In a motorcar, the
chemical energy stored in the petrol is cionvewr4ted to heat, which in turn is
converted to mechanical energy used to drive the vehicles.
5.3
SOLAR ENERGY: -
This is form of energy
that came to use from the sun. To day we have solar energy heaters, which
convert solar energy to heater energy. Solar energy
calculators and watches that convert the solar energy to electrical energy.
The plants make use of the solar energy to manufacture their own food.
Drilling is the operation hole making a hole in a material. It must not
be confused with boring which is the operation of enlarging a hole, which has
been previously made. A drill does not produce a very accurate hole. When an
accurate hole is required reaming or boring must follow the drilling operation.
6.1 SCREW
THREAD: -
The
pitch is the distance measured from a point on one thread to the same point on
the next thread. When a bolt has single continuous thread the pitch is the
distance that the nut moves in one complete revolution. The pitch is usually
given millimeters.
A screw thread may have a fine pitch
or a coarse pitch. When the pitch is fine the nut moves only a short distance
for each turn of the screw, whilst with a coarse pitch the nut’ greater locking
power than coarse threads and hence are used for screws which are subject to
vibration.
A thread is groove winding round a
cylindrical object and is used for fastening. Four types of screws thread and
their uses are:
(a) Vee – thread is used
for general engineering.
(b) Square – thread is used for machines and power
transmission.
(c) Buttress – thread is used for quick release
mechanisms.
(d) ACME – thread is used in transmission of power
and motion.
Drill is a cutting tool used in
boring a cylindrical hole in a metal or material. It is fitted to and powered
by a drilling machine. Some of the comm. on types of drills are:
(a) Twist drill.
(b) Flat drill.
(c) Combination drill.
(d) Counter drill.
Part of drill: Cutting lip, body,
neck, shark and tang.
Types of drilling machines are:
(a) Hand drilling machine.
(b) Sensitive drilling machine.
(c) Multiple – spindle-drilling machine.
(d) Radial drilling machine.
(e) Back geared drilling machine.
Tap is a hand tool used in cutting
internal threads. It is normally held by a tap wrench for this operation.
Die is used in cutting external
thread by hand method. It is fitted to a diestock.
ASSESSMENT FOR EVALUATION
1. State the difference between kinetic
energy from potential energy?
2. State the principle of conservation
of energy?
3. Define material and explain plastic
material?
4. Define the following: Drilling and
Boring?
5. List the types of thread used in
technology?
6. Draw a drill and label it parts?
SOLUTION
1. Kinetic energy is the energy
possessed by a moving BODY. If a body is in motion, the body is said to possess
kinetic energy.
2. The principle of conservation of energy
stated that energy could neither be created nor destroyed. Energy can only be
change from one form to another.
3. Material can be defined as anything
that has weight, can be seen, touch, occupied spaces and used for various
construction works.
4. Drilling is the operation of making a
hole in a material.
Boring is the operation of enlarging
a hole which has been previously made.
5. Vee – thread, Square thread, Buttress
thread, and ACME – thread.
7.0 INTRODUCTION TO ELECTRICITY & MAGNETISM
Atom
is the smallest particle of a element, structurally it
has proton and neuron in it nucleus.
Water can be separated in to hydrogen
and oxygen gases, and common salt into chloride and sodium, and sugar into
carbon and water. But, could never obtain simpler substances
from hydrogen, oxygen, carbon and sodium. These simple substances are
called elements. Such substances as water of more than one element are called
compounds.
Atoms of different element may
combine to form compounds. For example, two hydrogen atoms may combine with one
oxygen atom and form a molecule of water. A molecule is the smallest particles
into which a compound of atoms can be divided and still keep its quantities.
As early started, electrons goes
round the nucleus of atoms but, if the electrons are far away from the nucleus,
the force of attachment will become weak and these electrons would fall away as
free electrons.
Electrically all materials are
classified into conductors and insulators. Conductors are materials that
allowed electric current to flow through it while, insulators are materials
that don’t allowed electric current to flow through it. The possibility of
current flowing through conductors is because of the many free electrons while,
negligible number of it is found in insulator
If you rub two different materials
together electrons may be forced out of their orbits from one material into the
other material and retained there. These materials are then said to be
electrified.
The material, which captures or gains
the electrons, acquires a positive charge and material, which loses electrons,
acquires a negative charge. This is the distribution of electric charge and is
called static electricity. In the case where the excess electrons, which make
up the negative charge move across very rapidly to the material with fewer
electrons the actual transfer, or crossing over of the electrons from the
negative charge is called an electrical discharge.
A magnet is a metallic object made of
iron or steel that has the property of attracting other metallic objects.
Substances that can be attracted by a
magnet are said to be magnet to attract magnetic substances is called magnetism.
All magnets which do not depend on electrical energy to keep this property are
called permanent magnets while; magnets which are made by passing an electric
current through a coil of wire are called electro magnets.
If you sprinkle iron fillings on a
magnet, you will notice that the iron fillings are not attracted uninformally
to the whole surface but rather tend to cluster at each end of the magnet. The
two ends are called the poles of the magnet.
Some substances are not magnetic and
they are equally made up of atoms because, the direction of the magnetic field
around a moving electron depends upon the direction of the electron, that is
whether clockwise or anti-clockwise, around the nucleus.
So, if half of the electrons of an
atom rotate in one direction, and the other half in the other direction, the
magnetic fields will cancel each other out, leaving no resultant field around
the atom. Hence the atom becomes non-magnetized.
If more electrons rotate in one
direction than in other direction, the atom will have a resultant magnetic
field and will be magnetic.
8.0 RELATIONSHIP BETWEEN ELECTRICITY &
MAGNETISMS
Microphones
and loudspeakers use at public meetings are few instruments that work on the
combined principles of magnetism and electricity.
Electric current flows will always
produce some form of magnetism. If electric current flow through a conductor
the conductor acted like a magnet.
If two conductors run side by side,
and currents flow through them in the same direction, then the two conductors
attract each other; if the current flow in opposite direction, the conductors
will repel each other. The attraction and repulsion in both cases are due to
the magnetic lines of force produced when there is current flow. These magnetic
forces are quite different from electric forced between charges at rest. Two
static negative charges repel each other.
Magnetic lines of forces are
developed at every point along a current carrying conductor. The fields consist
of concentric circles in a plane perpendicular to the conductor. These magnetic field so formed are not very useful. In fact
in some cases they are considered as a disturbance. For example, if you are in
a car with its radio on and you happened to pass under a high voltage
transmission line you will notice that for some seconds the sound of the radio
is distorted. It is the magnetic lines of force from the high voltage
transmission lines that caused the interference.
Electro magnetism is the generation
of magnetism when electric current flows through a conductor and no magnetism
when there is no current flow.
1. More in an orderly way in the
workshop; never dash or run. Always look around you before moving to ensure
that no obstacles are there.
2. If it is necessary to carry a chisel
or gouge in the workshop, carry it with the cutting edge low and facing
downwards.
3. Replace all unnecessary tools in
their respective places.
4. Never lean a sash cramp or length of
wood against a bench, cupboard or wall.
5. When using chisels and gouges always
keep both hands behind the cutting edge.
6. When using saws ensure that the free
hand is not in front of or below the saw.
7. When carrying length of timber in the
workshop carry them in an upright position.
8. Never place work or timber in an
unsafe position on cupboards or shelves.
9. When using machines ensure that the
proper guards are in position.
10. Makes certain that you know the positions of
the safety buttons in the workshop, which cut of the power of every machine.
11. Never throw anything in the workshop.
12. Use the tools in an unhurried and orderly way.
13. Make certain that you know the fire drill.
14. Should any kind of accident or injury occur
inform the teacher immediately.
15. Never leave any tools projecting over the
bench or turn round quickly with care in your hand.
Food
production is of primary importance to every nation. In this country up to half
of the workforce may be engaged in agriculture but the productivity remain low. The use of crude farming tools is just one of
the reasons. Mechanization will go along way in to improving our agriculture
produce. Devices used are different operations like planting, harvesting,
storage and preservation.
10.1 PLANTING
Planting
involves ploughing (tilling) and sowing of the crops.
Ploughing
is the process of loosening and aerating the soil. It can be alone manually
using hoes. Ploughs are now available. They can be drawn by animals (e.g.
horse) or tractor. In fact the tractor can be used in powering most of the
machines used in the farm.
Sowing
of seeds is done using machetes or piece of stick. A machine called auto-fed
jab planter has been developed to sow seeds and meter fertilizer.
10.2 HARVESTING
Tools
used in harvesting depend on the crops. Grains can generally be harvested by
hand picking. Trolleys and wheelbarrows for carrying can facilitate picking and
colleting harvested items.
Harvesting
of farm potatoes, cocoyams and cassava involves digging the soil to pull out
the tubers and removing of the soil.
Combine
harvesters are machineries used in the cutting, gathering, and threshing of
grains.
10.3 STORAGE
Food harvest at one period is needed at other periods. Also food produced in one area is eaten in other areas. This calls for storage facilities.
Before
food can be stored safely, it is dried to some degree. The aim of storage is to
keep food away from insects rats; rain e.t.c.Yam tubers are stored in the
barns. The barn shelters yam from direct heat of the sun and allows circulation
of air.
Grains
are stored in sacks and silos. Kola nuts are stored in fresh leaves to retain
their moisture.
10.4 PRESERVATION:
Some
food items cannot be stored for a long time for instance meat and fish.
Spoilage a these items are caused by micro – organisms
like bacteria, fungi e.t.c. These organisms need moisture and warm temperature
for rapid growth. They are killed by excess heat.
Preservation can be achieved by
controlling the temperature, reduced the moisture (drying), keeping the food
out of reach of the organisms, or adding chemical that kill them.
Common methods of preservations are:
(a) Drying: This can be done by exposing the food
to the sun or using artificial drier. Examples of food that can be dried are
pepper, fish, and vegetables.
(b) Smoking: This is the process of drying meat
or fish by burning firewood or charcoal.
(c) Salting: This is the process of using dry
meat and fish. High concentration of salt kills micro-organisms. Sugar can be
used in a similar way in preserving fruits.
(d) Pasteurization: This is the process of
heating milk to a relatively high temperature below boiling point for a long
time. This kills most of the organisms. Pasteurized milk can be preserved in
the refrigeration.
(e) Canning and bottling: The food items ceiled
in a can/bottle and heated to a very high temperature to kill the micro –
organisms. Examples of food items ceiled in a can are tomatoes, fish, meat,
vegetables, and juice e.t.c.
(f) Refrigeration and freezing: This is the
process of reducing the temperature of the food to reduce the activities of
micro – organisms. Examples of food preserved by refrigerators are meat, fish,
vegetables, fruits, and juice e.t.c.
11.0 DRAWING EQUIPMENTS AND MATERIALS
Neatness
and accuracy are essential in all geometrical and technical drawing, and in
order to achieve a high standard in both there directions it is important that
the right equipment is used in the correct manner.
A good and accurate drawing means
communicating because, drawing is a universal language. To communicate by
drawing, it involved constant practice with the aid of drawing instruments and
materials listed below:
1. Drawing board.
2. Drawing paper.
3. Tee – square.
4. Chips.
5. Protractor.
6. Scale rule.
7. Pencils.
8. Set – Square.
Drawing board:
This should be of good quality wood, smooth and not too soft.
Drawing boards are various sizes; the most suitable size is A2 – 420 x 594mm. Specially fitted metal edges protect the vertical sides of
the board and allows the Tee – Square to more up and down easily. The board and
should be kept clean and in good condition. The board should be use for drawing
and not for any other purpose.
Tee – square:
Is used for drawing parallel lines across the
paper and assist in the drawing of angles and parallel lines with the aid of
the set – stock.
Drawing pencils:
Two types of pencil are
required, a 2H for drawing lines and HB for lettering and dimensioning.
Set – square:
Are triangular instrument used for vertical
and diagonal lines across the paper. Suitable sizes being set – squares (60o
and 45o) 200mm.
Chips:
To begin drawing, the paper is placed squarely
on the board and secured by means of spring steel drawing chips. It is possible
to with paper without removing the chips.
Protractor:
Is an instrument graduated from left to right
or from right to left (0o – 180o) used for measuring angles.
Scale rule:
It is flat and straight
instrument graduated in cm, dm, mm or inch, used in drawing a straight line or determined
the length of a straight line.
Drawing paper:
It varies in relation to
the size of the drawing board, usually from quarter to full imperial. Suitable
metric sizes of drawing paper are: A2, A3 A4. Apart from size, we have the
tracing paper and the trans – parent cloth backed
drawing paper.
Machine
is any device by means of which a force applied at one point can be used to
overcome a force at same other point.
12.1 LEVER:
Simplest form of lever in common use
is a steel know as a crowbar but, the term lever may
be applied at any rigid body which is pivoted about a point called the fulcrum.
A force called the effort is applied at one point on the lever and this
overcomes a force called the load at same other point.
12.2 PULLEYS:
Pulley is a wheel with a grooved rim,
and there may be several mounted in a frame work called a block. The effort is applied
to a rope, which passes over the pulleys.
Single fixed pulley: This is often
used for the purpose of raising small loads contained in a bucket or basket to
the top of a building during construction or repair work. The tension is the
same through out the rope. So that, neglecting the weight of the pulley
bearings, we have,
Load
= effort
And mechanical advantage = load
Effort = 1
In this case, although the effort
applied is equal to the load raised, we obtain the greater convenience and ease
of being able to stand on the ground and pull downwards, instead of having to
have the load upwards from the top of the building.
12.3 INCLINED PLANE:
The velocity ratio is given by,
Velocity ratio = dist. moved by
effort = length of plane (L)
dist. moved by
load height of plane (h)
Thus, for a “perfect” inclined plane,
load x distance load moves =
effort
x distance effort moves.
Therefore mechanical advantage = load = l
effort h
A
gear is a wheel fixed in machines to make different parts move at different
directions.
Gears are used to transmit power from the point where such power is being developed to a point where it is used to do work. Gears are used to harness efficient engine speeds from slow speed tasks such as in car pulling through sand or mud, climbing a for the automobile transmission system.
13.1 DRIVES
Belt Drive:
The transmission of motor and power by belt is achieved by the use of pulleys. The application of endless belt and pulleys is now limited to the dynamo, fan and water pump.
Chain
Drive
This is a more positive drive employing a sprocket, a chain wheel and a air wheel is the driver.
Gear Drive:
Belts may slip and the chain may stretch or be noisy in operation but a gear drive supersedes all. Gear drives are used for the automobile transmission system.
13.2 VELOCITY RATIO
The
velocity ratio (V.R) of two rotating shafts can be defined as the number of
turns of one shaft as the other shaft makes only one revolution. V.R of belt
is given as:
V.R
= revs
of driver pulley = dia of driver
pulley
revs of
driver pulley dia
of driver pulley
V.R of chains is given as:
V.R = revs of sprocket = no.
of teeth in chain
Revs
of chains wheel no. of teeth in
sprocket
V.R of gear wheel is given as:
V.R = revs of driver gear = no.
of teeth in driver
Revs of driven gear no.
of teeth in driver gear.
Example 1.
The
fan – alternator pulley of a crankshaft or a certain engine is 300mm diameter
and the driven pulley on the alternator is 200mm. If the engine speed is
3000revs/min, calculate the speed of the alternator?
V.R = revs of driver pulley = dia of driven pulley
Revs
of driven pulley dia
of driver pulley
: . V.R = 3000 = 200
x 300
200 x
= 3000 x 300
200
= 900 000
200 x 900
000
200 200
: . alterternator speed
x = 4500 revs / min
Example 2.
An engine uses a timing chair drive
and has a grakhaft sprocket of 23 teeth driving a
chair eheal on the crankshaft also of 46 teeth. If
the engine speed is 3000 revs / min, what is the speed of the crankshaft?
V. R = revs of sprocket
= no of teeth in chair
wheel
Revs
of chair wheel no of teeth in sprocket
: . V.R = 3000 = 46
x 23
46x = 3000
x 23
46x = 69000
46x = 69000
46 46
: . Camshaft Speed x = 1500 revs /min
Example 3.
The
timing gear wheal of a petrol engine crankshaft has 27 teeth and the meshing
gear wheel on the crankshaft has 54 teeth. If the speed of the crankshaft is
found to be 1200 revs / min, calculate the actual speed of engine.
V. R = revs of driver gear = no
of teeth in driver gear
Revs
of driver gear no
of teeth in driver gear
: . V.R =
x = 54
1200 27
27x = 1200 x 54
27x = 64800
27x = 64800
27 27
: . Engine speed x = 2400 revs/mm
The
word “force” generally denotes a push or a pull. We cannot describe force as we
can describe some material object such as an apple. We can only say what force
can do. When a body is acted upon by a resultant force it will begin to move.
If the body is already moving a force may alter its speed or alter its
direction of motion or else bring it to rest. We therefore define force as
follows:
Force is that which changes a body
state of rest or of uniform motion in a straight line.
The limit of force is called the
Friction is the name given to the
force, which opposes the relatives sliding motion of two surfaces in contact
with one another.
The two types of frictions are:
Static friction and
sliding friction.
If a wood block is place on a flat
surface table and force applied on it, at first the wood block will continue to
remain at rest since an equal increase but opposite directed force of friction
comes into action at the under surface of the block. At this point the
frictional and the force of pull are in equilibrium.
If we continue to increase the force
of pull, a stage will be reached when the block just begins to slip. At this
point, the friction brought into play he’s reached its maximum value for the
two surfaces concerned, and this is called the static friction.
Sliding friction is the less
force-applied o on the wood block as it continues slips at a steady speed.
14.1 DISADAVANTAGES OF FRICTION
(a)
Causing
extra effort – friction always tends to prevent movement of one part over
another. Extra effort is therefore needed to cause movement. This is one reason
why no mechanism or machine can be 100% efficient.
(b)
Wear – friction causes wear between two
moving surfaces. In some cases it can cause moving parts to seize up.
(c)
Heat generation – friction often causes heat
to be generated in moving parts. In many cases this heat has to be removed by
using a cooling liquid.
14.2 THE EFFECTS OF FRICTION
It
will be seen that actual contact between the faces of the two blocks takes
place on only a few very small area. Even when quite small forces hold the
surfaces together very high pressures are created on the area in contact ( this is rather like a young lady who is comparatively
light in weight walking across a floor in stiletto heels. The small area in
contact with the floor causes a high pressure at the contact points cause the two surfaces to be cold – welded together which
causes a further resistance to movement. Before on surface greater enough will
slide over the other a force greater enough to shear the cold welds must be
applied. If the two surfaces are made from different metals particles of the
soften material will be transferred to the harder material. This wear takes
place on the surface of the soften material.
14.3 LUBRICATION
While,
friction is highly essential in some circumstances, it is a great nuisance in
other. In a car engine, for example, oil under pressure is supplied
continuously to all bearing surfaces. Failure of the oil supply will allow
metal – to – metal contact and the resultant friction often raised the
temperature and causes the bearing and pistons to wear away or “seize up”.
14.4 CO
– EFFICIENT OF FRICTION
T
ratio of the static and sliding friction to the force pressing the surfaces together
are called the coefficients. Coefficient letter “μ”. Thus,
μ =
F
R
Where F = force of friction
R
= force of pressing surfaces together.
Example 1.
The main horizontal retarding force
applied to a motor vehicle to bring it to the point of skidding is 60&5N.
The mass of the vehicle is 1 tone. What is the coefficient of friction between
the types and road?
Vertical downward force = mass x
gravity force
= 1x 1000 x 9.81
Coefficient of friction = horizontal force
downward
force
= 6085N
1 x 1000 x 9.81
= 0.6203
Example 2.
A block of steel having a mass of
10kg is placed on a horizontal surface. A force of 19.62N is needed to just
keep the block moving steadily.
Calculate the coefficient of
friction.
The weight of the block is:
Weight = 9.81 x
mass of block
=
9.81 x 10 kg
= 98.1
Where force = 19.62 N
The coefficient of friction is μ
= F
W
: . μ = 19.62
98.1
= 0.2
When
two lines meet they formed n angle.
An acute angle is less than 90o;
an Obtuse angle greater than 90o is an angle greater than 180o
but less than 360o.
Angles are measured in degree. There
are 360o in a circle. Angles can be constructed and measured with measuring
instrument.
15.1 CONSTRUCTION
To
bisect a given angle:
(i)
Draw
the given angle A B C
(ii)
With
center A and by convenient radius draw an arc to cut AB of D and AC at E.
(iii)
With
center D and any radius draw an arc.
(iv)
With
center E and the same radius draw an arc to intersect the previous one F.
(v)
Join
AF. This is the bisector.
To construct an angle of 45o
(i)
Construct
a right angle BAC.
(ii)
Bisect
the right angle to obtain angle 45o.
To construct an angle of
60o
(i)
Draw
a line AB.
(ii)
Indicate
point C any where on AB.
(iii)
With
center C and any convenient radius draw an arc to cut AB at D.
(iv)
With
center D and the same radius draw arc to cut the previous one at E.
(v)
Draw
a line from C through E (line CF). FCB is the required 600 angle.
To construct an angle of
30o
(i)
Construct
an angle of 60o.
(ii)
Bisect
the 60o angle.
(iii)
Angle
ABC is the required 300 angle .
To construct angle of 15o
(i)
Construct
an angle of 30o.
(ii)
Bisect
the 30o angle.
(iii)
Angle
1,2,3 is the required 150 angle.
15.2 TRIANGLES
A
triangle is a plane rectilinear figure with 3 sides and 3 angles.
A right – angled triangle has 1 angle
90o. The side opposite the right angle is called hypotenuse.
An isosceles triangle has 2 equal
sides and angles.
A scalene triangle has 3 unequal
sides and angles.
15.3 CIRCLE
A
circle is a plane figure bounded by a curved line called the circumference,
which is always equal distance from the center, meting the circumference at the
ends.
A radius is a straight line drawn
from the center to the circumference.
An arc is any part of the
circumference.
A chord is any straight line drawn
across the circle, meeting the circumference at both ends.
A tangent is a straight line, which
touches the circumference. it is always at right
angles to the radius.
A segment is part of a circle bounded
by an arc and a chord.
A sector is part of a circle bounded
by two radii and an arc.
A quadrant is part of a circle
bounded by two radii at right angles and an arc.
15.4 QUADRILATERALS
There
are plane figure with four sides e.g. square,
rectangle, Rhombus, parallelogram, trapezium, trapezoid and deltoid.
15.5 POLYGONS
A
polygon is a plane rectilinearly figure with more than
four sides.
Regular polygons have equal sides and angles.
A pentagon has 5 sides, a hexagon 8,
a heptagon 7, an octagon 8, nonagon 9 and a decagon 10.