Methods used to facilitate work

You have already learnt that machines are used to make tasks easier. Some examples of simple machines are lever, inclined plane, pulley and wheel and axel.More over, you know that energy could be transmitted using endless chains, cog wheels, rods, fluids and air. Complex machines could be assembled using simple
machines. Man uses machines and mechanical devices to fulfil his needs in day today life. Now, let us consider some machines and mechanical devices used by man in the fields of building construction, repairing motor vehicles and agriculture.

Machines used in building construction

You may have seen that machines are used for levelling the sites, digging pits and ditches, piling, masonry and carpentry work in the field of construction

Some machines used in construction sites

The table you prepared for the above assignment may contain mammoty, pickaxe,crow-bar, wheel barrow, claw-hammer, pulley,hand drill, electric drill and chisel as machines. There may be bulldozer, tractor, backhoe, crane, pile driver and concrete mixer machines in your table. Let us now, consider about a few of those machines, or devices.

1. Bulldozer
Bulldozer is used to fell down trees and boulders, to load soil, to push boulders and soil and to level the sites. See the fig  below.

A bulldozer

A tree or a boulder could be fell down by raising the blade of the bulldozer and pushing with it. Land could be bladed and

levelled using the blade of the dozer. To move various parts,
there are joints made in such a way like the elbow joint of man (E.g 3:2.3 and 3.2.4) There should be relative motions of the
steel bars of a bulldozer for raising and lowering of various things. Those steel bars are riveted to each other using bolts. Such a joint is shown in fig 3.2.3. Suppose the load at C is to
be raised. For this, the bar AC should be moved away from the bar AB. In other words, the angle BAC should be increased. To do this, the length of the jack fitted to the points D and E should be increased. This is done by pumping oil into
the cylinder of the jack. The operator of the bulldozer does this by pulling a lever. Here, this machine acts as a lever of 3rd order, just like the elbow joint of man (Fig 3.2.4). Force is
supplied to the hydrolic jack, which acts as the effort, by transmission of fluid.

2. Backhoe machine                          

Backhoe machine is used to cut ditches for foundations and to dig holes for piles. For this purpose, there is a narrow claw - like cutting tool at the end of a long arm. The movement of this part is done in the same way like the blade of bulldozer.There are two endless broad iron chains, instead of tyres, in most of the backhoes. These chains increase the grip between the machine and the ground. Hence it increases the friction. More over, the wide surface area of the chain decreases the pressure on the ground. Therefore, the machine does not sink into the soil.

3. Pile driver

When storied buildings are constructed, large concrete piles are sunk into the soil to hold the weight of the building. In unstable soils, these piles are sunk to reach the bed rock. To drive the pile into the soil, heavy load is lifted by a crane, and dropped on to the pile head under gravity. This heavy load is known as pile driver.

There are pulleys and pulley systems in the crane for the lifting of pile driver. If the pressure excerted by the pile on the soil is increased, it will easily sink into the soil. For this purpose, the bottom of the pile is pointed. The function of this pointed part is similar to an inclined plane. A large amount of kinetic energy is released due to the heavy mass of the pile driver and the high velocity of the falling pile driver. This kinetic energy is exerted on to the pile head. As a result, pile sink into the soil (Fig 3.2.7).This process is very much similar to sink a wedge in soil. (The steel cap on the pile head prevents damaging the pile)

Velocity

Speed does not refer to the moving direction of the object. The term velocity isused to indicate both the direction and the magnitude of the object.The velocity of an object could be represented by using the
following equation.

The SI unit for velocity is metres per second (m s-1)Velocity is the displacement per unit time or is the rate of change of displacement.Since displacement has a direction, the direction of velocity is also in similar to
that of the displacement. That means, velocity has a magnitude and a direction.Therefore, velocity is a vector quantity.
Refer to the diagram given in Fig           
3.1.3. It shows two vehicles with the
velocities of 40 km h-1 travelling in the
opposite directions.
Are the two velocities same?
clarify your answer.
Though the magnitudes of the two velocities are same, the directions are
different. Therefore, the velocities are not equal to each other.
Acceleration and deceleration
According to the experience of travelling by vehicles we know that the speed of a vehicle changes from time to time. The driver can increase the speed by pressing onthe accelerator and he can decrease the speed by using the brakes.When a vehicle starts and drive ahead, its speed will increase. It is called 'Acceleration'.
Acceleration
The following table shows the change of velocity of a train which started its motion from rest, with time

 Note that in the above example,
• The train starts from rest.
• Velocity has increased uniformly.
• Every second, the velocity has increased by 3 m s-1
.
Thus, the object has accelerated at 3 metres per second in every second.Acceleration of an object could be represented by the following equation.

SI unit for acceleration is metres per square second (m s-2)
Acceleration is defined as the change of velocity per unit time or as the
rate of change of velocity. Acceleration is a vector quantity.
When a driver presses the accelerator, the velocity of the vehicle is increased as well. When a car drives away from the traffic lights, its velocity gradually increases.Then it is said that the vehicle is accelerating.Refer to the velocity between 2nd and 5th seconds in the table 3.1.1












Deceleration
What happens when you apply brakes on a moving vehicle. The vehicle will slow down. This is the opposite of acceleration. It is known as deceleration.
e. g. The speedometer of a vehicle indicates 54 km h-1 at point A. After
applying brakes it arrives at point B at a speed of 36 km h-1 in 4 seconds. Assume that the velocity has decreased uniformly.

Energy, work and force

Linear motion

Observe the things around you. Some of the objects you see are stationery.For example, buildings, statues and rocks. Some of the objects are moving. A fanrotating, vehicles moving on the road and birds flying are some examples of moving objects. If you observe the motion of the moving objects more closely, you will be
able to observe the nature of their motion more clearly (fig 3.1.1). The rotating fan shows a rotational motion. Motion of planets around the sun is referred to as revolution.The motion of a pendulum bob is an oscillation. A runner of 100 metres running along a straight track undergoes a linear motion. In this chapter let us
understand some concepts related to the linear motion.

Distance and Displacement
Assume that you are walking to school. The length of the path that you moved on your way is known as ‘distance’. Therefore, the length moved by a moving object is the distance travelled by it.Consider the linear motion of a motor vehicle shown in fig 3.1.2. The vehiclemoves 4 km to the East, 2 km to the South and then 4 km to the west.

The magnitude of the distance moved by the motor vehicle   = (4+ 2 + 4 ) km
                                                                                           = 10 km
But, when considering the direction of motion of the vehicle, at the beginning it moved to the East, then to the South and finally to the West. Hence, it does not show the motion in a definite direction. Therefore, the quantity of distance has a magnitude but no definite direction.Such quantities which have a magnitude but no direction are called scalar quantities. Accordingly, distance is a scalar quantity.Now let us consider the quantity called displacement.Refer to the fig 3.1.2 again. Although the vehicle moved 10 km from the starting
point to the final point, the change in the position of the object is only 2 km towards the south direction.
Quantities with both a direction and a magnitude are known as vector quantities.Accordingly displacement is a vector quantity.
Solved problem 1
A student walks 2 km along a linear path to the West then turns around and walks 2 km along the same path to the East. Find the distance and the displacement of the student.
Distance travelled      = 2 km + 2 km      = 4 km
Displacement            = 0 km

Solved problem 2
A motor car travelled 10 km along a straight road to the East, turned around and travelled 7 km to the West.
Find the distance and the displacement of the car.
Distance travelled                          = 10 km + 7 km            = 17 km
Displacement                                = 3 km to the East

Speed

The rate of the change of distance is known as the speed. If the distance travelled per unit time is low the speed of the object is low. If the distance travelled per unit time is high, the speed of the object is high. Recall your experience of travelling in a bus. If you observe the speedometer you will realize that the speedometer reading is changing from moment to moment. The reading of the speedometer of the bus at a given time
shows its speed. If the speedometer reading is constant for a given period of time, we say that the bus has travelled at a constant speed.If an object moves equal distance in equal time intervals, it is said that the object
moves at a constant speed. The speed of an object could be given by the following equation

        Speed =          Distance travelled
                                  Time taken        

The speed of an object is the distance travelled in a unit time .The SI unit of speed is metres per second. (m s-1).
Average Speed
Vehicles do not always travel at same speed. Sometimes they travel faster sometimes slower. Therefore we have to refer an average speed rather than the speed.The average speed of an object could be calculated by using the following equation

Average speed =                                  Total distance moved
                                                                Total time taken   
SI unit for average speed is also metres per second.e.g. The average speed of a van travelling 60 m in 6 s could be calculated as follows,

Therefore the average speed of the van is 10 m s-1 If the distance travelled are long, we indicate the speed in kilometres per hour(km h-1) Speed has a magnitude but no direction. Hence, it is a scalar quantity.

Leo Constellation

If you raise your eyes upwards in the sky along
the two indicator stars of the Great Bear constellation,you will see a sickle shaped bright constellation. To the east of this Constellation, three bright stars can be seen at the corners of the right angled triangle. This sickle and the triangle together form the Leo constellation.The brightest star in the Leo constellation is Regulus. At this time, a slanted cross on the southern side of the sky will be visible.This constellation is called the Southern
Cross.Two bright stars will be seen closer to the southern cross and east of it. Out of these, further away from the Southern cross is the Alpha Centauri. It is the brightest star of the Centaurus constellation sorrounding the Southern Cross. If this is examined with the telescope, it is
found to be made up of three stars.Out of the three stars the star closer to Earth is Proxima Centauri. It is the closest of the stars that are visible to the Earth.


Do you know?
The distance from the earth to the stars and the distance between stars is
measured in units called light years. A light year is, the distance that light travels in one year, which has a speed of 300000 kilometres per second.
That is 300000 x 60 x 60 x 24 x 365 kilometres.

Proxima Centauri is at a distance of 4.2 light years and Sirius is at a distance of 8.7 light years from the earth.

Ursa major

At the above mentioned months and time the Great Bear or Ursa Major composed of seven bright stars is visible high up in the sky to the north direction. The four stars forming a rectangle
depicts the body of the bear, while the remaining three will depict the tail. In some countries this constellation is
termed as Big dipper or as Saptharishi (Seven rishis).The two stars on the side of the head in the rectangle of great bear are called ‘indicator stars’.Connect these two stars by an imaginery line and
extend this line about five times downwards. It will lead you to the Pole star or Polaris which is a bright star.The special feature about this star is that its position never changes. Even in Sri lanka this star is found very low down in the horizon. But as you proceed to the countries in the North direction of the earth, it moves up from the horizon and in the north pole it is right on top of the sky.The reason for this star to remain stationery is because it is located directly above the North pole on the axis of rotation of the earth. Hence it is useful for navigators and for people travelling in deserts in the night. By this they can identify the North direction as well as the lattitude where they are. Pole star is situated in the constellation called little Bear or Ursa Minor.This is at the end of the bear’s tail.

Gemini/Canis major/

 Gemini


Once you identify the head of orion, north of it and slightly to
the East, two bright stars close to each other are visible. They are Castor and Pollux. These two stars indicate the heads of the twins in the Gemini constellation










Canis major

Now connect the three stars in the belt of orion and took along the line towards
the east. Now, you will observe the brightest star in the sky. This is Sirius. It belongs to the constellation Canis Major .

Taurus Constellation.

 Now, look at the north direction the  west of the orion. You will see a group

of stars in the shape of a letter ‘V’. The bright red star in the ‘v’ is Alpha centori or Aldebaran. This is supposed to depict one eye of an ox which is about to attack
orion

The face of the ox is denoted by the five stars in the
shape of letter ‘V’. If you examine closer you would be
able to find the two stars fairly apart at the end of the
horn of the ox. In the Taurus constellation there is a very
attractive star group called pleiades. When observed
with the telescope pleiades constellation appears as to consisting of more than two hundred stars. The maximum number of stars that can be observed by the naked eye
is nearly nine. The brightest star of this group is Tori

Observe the sky around 8 p.m. in the months of February and March. You can identify the brightest star sirius. As you go on observing from the top to down you will be able to identify the second brightest star Canopus in the sky. If you examine it carefully you will see that its colour changes constantly. If you can connect the stars Sirius and Canopus by an imaginery line and extend that line downards you are getting close to the south pole of the sky. By this you can identify the south direction of the sky in the night.
Given below are some constellations you will see in the mid - night sky in the months of February and March. They can be observed in the months of May and June around 8 p.m. in the night.

constellation

Orion

In the months of February and March around 8 p.m. in
the night this constellation which forms a pattern resembling a
hunter will be seen in the sky . It has seven very bright stars. The two stars on his shoulders and the two stars on his knees appear as four corners of a square. The belt of the hunter is made up of three bright stars. The head is indicated by three stars which are not very bright. The case of the sword hanging from the belt contains three small stars. Now, you can build up an imaginary picture of the hunter. Since the head of orion is directed to the north direction, this constellation helps
to identify the North. The betelgeuse star indicating the right shoulder be named as a (alpha) orionis. This is a giant red star. The star indicating the left leg is b (beta) orionis or Rigel is a blue giant star. These two stars are among the brightest twenty stars in the sky.
About Orion...According to Greek mythiology orion is an expert warrior and a hunter. He was the son of god Neptune, who was the God of the oceans. The other Gods who noted his talents were jealous and killed him using a poisonous scorpion. But Goddess Diana placed him among the stars in the sky and made him immortal. At the sametime she placed the scorpion on the opposite side of the sky so that it cannot get closed to orion. Even today, when orion sets in the western sky, scorpion rises up in the eastern sky.

Do you know? The Greek alphabet

Identifying star patterns

One of the items in the educational trip
organised for the students of grade 9 in Saman Vidyalaya was a visit to the planetarium.All students entered the hall of the planetarium and took their seats. They were observing the roof of the planetarium. It was a white hemisphere.
The hall became gradually dark accompanied by lovely music. The
‘Planetarium sky’ got lit up by stars one by one, till the white area was completly filled with stars. The lecturer of the planetarium started his lecture. “We
welcome all of you to our planetarium today. First of all, let us identify the 4 directions of our planetarium sky.”
Having said this, he directed the special torch he held in his hand up to the planetarium sky. A small arrow appeared in the sky. He directed the torch to the letters N, S, E, W
and drew the attention of the audience to them. Students observed that all the stars appearing were moving from the east to the west direction. The lecturer explained that the stars in the night sky showed as if they
appeared to move from the east to the west because the earth is rotating from the west to the east. This is similar to what we observe when we are travelling in a vehicle, the trees and houses on either sides of the road appear to move backwards.

Do yo know ?

In a planetarium, it is possible to view the sky on any

day, at any time and at any place. This is done by an

instrument called the Universal Projector. This

instrument is mounted on a stage at the centre of the planetarium. From here it is possible to observe the

eclipses of the sun and the moon, meteorite rains, comets as well as the view of the solor system to a person observing it from outside, and the view observed if one were to travel in a space craft in a journey through the solar system.To observe these views get into the web www.starrynight.com. You can obtain compact disc containing all these information from the Arthur C.Clerk Centre.

To study about the star patterns, observing the night sky is a ‘must’. The instructions you have to follow are given below.
• Select a day close to new moon (Amawaka) day.
• Cover the face of your torch with a red 
   coloured cellophane paper.
• Stand on a stage during observations in order to protect yourself from snakes,
   poisonous animals and thorny bushes.
• Be prepared for sudden changes of weather.
• Get a photocopy of the star maps provided in this book and use them.
• Keep a note book and a pencil.
• It is better if you use a compass to identify directions. If not, use the direction of the buildings 
  and trees you noted during the day. Once the star patterns are
identified they will help you to identify directions.The imaginery pictures built up by joining the stars observed in the night sky are known as constellations. These pictures may be of natural objects or characters from
mythology. under image shows some constellations that can be seen in the sky in the months of February and March around 8 p.m. in the night.

about the solar system

A star speckled night sky filled the minds of men with awe, not only in the past but
also at present. From the ancient time, man has observed stars and planets appearing
in the night sky and he has come up with various theories about them. Accordingly,
astronomy can be considered as the oldest science in the world.
It was the Greeks who introduced Astronomy as a science of studying the sun,
the moon and the stars. There is evidence to prove that they used the knowledge from
predecessors in Egypt and the Middle eastern countries for this purpose.
In the distant past, celestial bodies were venerated as Gods. The first philosopher
to attack the myths regarding these objects was a Greek scientist Thales (640 B:C).
According to his theory the earth is flat. It floats on the ocean like a ship. The sun, the
moon and the stars are balls of fire revolving around this flat earth.
The idea of a flat earth was rejected by the great philosopher and mathematician
Pythagorus (580- 500 B:C) who declared that the earth is a sphere. His name became
immortalised with the famous pythagorus theorem.
Another Greek philosopher Aristotle (384-322 B:C) also supported the idea of
a spherical earth and explained it more clearly. He stated that the edge of the shadow
of the earth falling on the moon during an eclipse being a part of a sphere is an
evidence of the spherical nature of the earth.
He further stated that if a person were to travel a certain distance from a point in
any direction the change of the ascending angle of a star is the same, as evidence for
the spherical shape of the earth.
The view of Aristotle was that the sun, the moon and the planets revolve round
the earth. This incorrect idea of a geo - centric (earth - centered) model prevailed for
about 2000 years.
The first astronomer who put forward the heliocentered idea (sun - centred) was
the Greek (national) Aristorcus of Samos (310-250 B:C) who stated that the earth
revolves round the sun.
He also stated that the stars appear to rise and set each day because of the rotation
of the earth. However, the heliocentred idea was not accepted due to lack of evidence.Although Aristotle presented this idea of a geo-centric model, it was further
established on a mathematical basis by Claudius Ptolemaeus (100-178 A:D) who also
named as Ptolemy. Ptolemy was also responsible for building up maps of the earth and
the celestial bodies.
Ptolemy was succesful in compiling a book called Almagest which was a
collection of all knowledge available at that time. He indicated the presence of 48
constellations in that book out of which 47 are still known by their original names.
His view was that the earth is at the centre of the universe and that the sun, the
moon and the planets known at that time revolved round the earth in crystal spheres.
The views of Aristotle and Ptolemy were accepted by the powerful religious
athorities at that time. Presenting any views against them was an act that could be
punished by law.The helio-centric model, that is, the universe and the other planets revolve around
the sun was strongly advocated by Polish Astronomer Nicolaus Copernicus
(1473- 1543 A:D). This was a radical and a courageous effort. This became a radical
effort because at that time it was believed that the earth we live in, moves through
space was an extremely novel idea. It became a courageous effort since at that time
speaking against the geo-centred idea that was accepted by the religious authorities
was an anti-religious crime that could be punished by law.
Copernicus argued that the sun is at the centre of the universe and that planets
revolve around it in mega circular orbits. He also stated that the further away a planet
is from the sun, the longer time it takes to revolve around the sun. As evidence for his
theory he showed that the closest planet to the sun being Mercury takes about 2
months, while the Saturn takes about 30 years to revolve around the sun, which is the
planet farthest from the sun known at that time.
This novel idea of Copernicus led to an intellectual revolution at that time. That is
why Copernicus is known as “the great man who rotates the earth”. However, his ideas
which contradicted the religious teaching, and therefore the book which contained his
ideas was published after his death.(A crater in the moon is named after Copernicus too)

After Copernicus, great astronomers such
as Tycho Brahe, Johannes Kelper and Gallelio
Galili continued to follow him and to improve
the field of astronomy as a science.
Tycho Brahe (1546 -1602 A:D) was also
a pioneer in constructing instruments
for studying about stars. He was able to record
the movement of nearly 700 stars and the solar
system correctly. He rendered a valuable
service at that time by correcting some of the
existing data on astronomy.
Brahe did not accept the helio-centric model
of Copernicus. He stated that the five planets
then discovered revolved around the sun and
that the sun and these planets revolved around
the earth once a year. (The ‘Tycho’ crater on
the moon is named after this astronomer)
Although Brahe’s ideas on the movement of planets were incorrect, the information
he gathered formed the ground work for later astronomers. Johannes Kelper made use
of his observations and measurements to establish the ideas of Copernicus in later years.
Johannes Kelper (1571-1630 A:D), a German astronomer was able to formulate
three laws of planetory motion.
The ideas of Kelper’s laws of planetary motion can be summerised as follows:
• Every planet moves in an elliptical orbit which keeps the sun at one focus.
• The planets which revolve around the sun in their orbits move faster when it is
closer to the sun, and move slowly when it is far away from the sun.
• The length of the year of the planets which are close to the sun is shorter than that
which are far of the planets away from the sun.