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| Length,Time, Weight Measuring Instruments |
LENGTH:
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| Length Page in my Physics-World Software |
When we
talk about a length we always compare one measurement with another.If you say
you are taller than someone else you mean that the distance from the soles of
your feet to the top of your head is greater than that distance on the other
person. If you wanted to find out if you are taller than a pen friend in
another town it would not be possible to compare your heights by standing side
by side .Instead you would both use a scale such as a ruler or a tape measure
to compare heights.In this case you would each compare your own height with a
standard length - a foot or metre.It would impossible to use this method if the
standard of lenght in one place was different from the standard in the other.So
it is most important to make sure that the standard length is the same
everywhere.
YARDS AND
METRES:
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| British Imperial System. |
The
imperial British system of measurement of length was based on the yard but in
1963 the yard was defined in terms of the meter.
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| Imperial standards of length 1876 in Trafalgar Square, London. |
The first
accurate standard yard was made in 1878 .It was a bronze bar exacly one yard
long kept by the government.This was called the primary standard. From it
lengths a yard long were measured onto other rods.These rods kept in the laboratories throughout the country, were called secondery standards.
In 1963
the yard was defined in terms of metre, one yard being equal to 0.9144 metre.
The metre is the standard unit of length used in Europian countries.
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| Metric Imperial US Customary Units. |
In 1927
the metre was redefined as the length of a platinum iridium bar kept in
Paris.This bar was also found to vary in length in tiny amounts. So in 1960 a
new type of definition was internationally agreed.This is based on the
wavelength of the light emitted by atoms .This length never varies ; the same
atom under the same condition always emits light of indentical wavelength.The
atom chosen is an isotope of gas Krypton.The metre is now defined as
1,650,763.73 wave-length emitted by this atom under certain conditions.
Astronomers
sometimes use another method of measuring of lengths when discussing the
distance of stars .This is the lightyear and is an enormous distance.It is the
distance travelled by light in one year .Light travels at a velocity of 300
million metres per second . As there are about 31.5 millions seconds in a year
, one light year is 9460 million million metres of about 6 million million
miles.
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| CALLIPER & MICROMETER |
CALLIPERS
& MICROMETER:
Callipers
are used for measuring diameters, either internal or external. The distance
between the jaws of the callipers is read on a scale marked on the instrument.
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| Callipers are used for measuring diameters, either internal or external |
A
micrometer is an instrument for measuring small distances very accurately. It
consists of a sleeve which rotates on a screw inside it .
3D Animation Showing the Work of CALLIPERS & MICROMETER
As the sleeve is rotated it moves forward until the tip of the micrometer just touches the object being measured. The width of the object is then given on the scale.
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| A micrometer is an instrument for measuring small distances very accurately |
As the sleeve is rotated it moves forward until the tip of the micrometer just touches the object being measured. The width of the object is then given on the scale.
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| Scale and Protector |
ELECTROMAGNETIC
SPECTRUM:
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| The electromagnetic spectrum |
The
electromagnetic spectrum . Radio wave have much longer wavelengths than light
waves which in turn have greater wavelengths than x-rays and gamma rays . The
visible part of the spectrum is very narrow compared with other parts.
TIME:
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| Time Page in my Physics-World Software |
In
ancient times,before clocks were invented,people knew that the seasons came and
went at regular intervals. The sun also rose and set regularly creating night
and day. Far back in prehistory, people realized that time could be measured
using these regular events. The length of time between the appearance of two
summers was called a year. The time between one sunrise and the next was called
a day.Another way of measuring time was by noting the occurrence of a new
moon.This happens at regular intervals of about 30 days.When some one said
"many moons have passed" he or she meant that that the moon had waxed
and waned many times.The word month comes from the word moon.
We know
know that these regular events are due to movements of the earth and moon.The
moon waxes and wanes as it moves round or orbits the earth. A day is the time
taken for the earth to spin round on its own axis it is also travelling around
the sun. A year is the time that its takes for the earth to make one complete
circuit of the sun.A year is the time that its takes for the earth to make one
complete circuit of the sun.It actually takes us 365(1/4) days to travel
completely round the sun.So every fourth year we have a leap year of 366
days.The extra day occurs as the 29 th February.This avoids the calendar
getting out of step with the movements of the earth and sun.
A day is
divided into 24 equals divisions of an hour.Each hour is divided into 60
minutes and each minute into 60 seconds.
MEASURING
DEVICES OF TIME:
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| Picture of Sundial |
One of
the first devices used to measure time was a Sundial.As the earth spins round
on its axis a shadow cast by the sun gradually moves round.This movement was
mapped out and used for telling the time.Other method of
measuring depend on the processess that occur at regular rates. A simple
example is burning down of a candle .If you have two similar candles you can
make a candle clock.Measure the time it takes for the first candle to burn down
a measured distance. It take say 3 hours to burn 3 cm. You now know the 1 cm is
burned in one hour.Mark your second candle with 1 cm marks. If you now light your second candle
you able to tell how much time has passed by seeing how many marks heve
disappered.Another regular process used to measure time is the passing of sand
through a small hole .An egg timer works in this way. A larger version of the
egg timer is called an hour glass.
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| Pendulum Clock |
The next
regular process use to measure time was
the swing of pendulum.This is the weight at the end of a stick or
string.Pendulums of the same length will always take the same time to swing
from one side to the other.No matter howfar they travel.To obtain different
periods of swing you need pendulums of different lengths .A pendulum about 25
cm long swings both way in a second. A 1 metre pendulum takes roughly twice as
long (about 2 seconds) . The pendulum of Big Ben in the houses of
parliament.London is 4 metres long .It takes 4 seconds to swing back and forth.
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| Fashion Watches Quartz Watches Wrist Watches Lady's Watches Jewelry Watches. |
The
clocks that scientists us to measure time are based on the vibrations of atoms . These vibrations are very regular and
atomic clocks are correct to one second in 3000 years.Quartz digital watches
measure time by counting the atomic vibrations of a quartz crystal.
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| Quartz digital watches |
EARTH
ORBIT:
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| Earth travels round the sun it creates night and day |
As the
earth travels round the sun it creates night and day .When one half of the
earth is in darkness the other half is in the sunlight . As the earth moves
around the sun it is also spinning on its own axis. Taking about 24 hours to
complete an entire revolution.As the sun`s ray shinestedily from one direction,
the spin of the earth has the effect of creating day and night on the earth
surface. It takes the earth 365 days, 5 hours, 48 minutes and 46 seconds to
complete each orbit around the sun. The earth travels around the sun . The
earth travels around the sun at a speed of 106 000 kph (66 000 mph).
SEASON:
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| Four Seasons |
MARCH 21
ST-- Spring in the northern hemisphere and autumn in the southern.
JUNE 21
ST -- The north pole is tilted towards
the sun and it is in summer in the northern hemisphere, winter in the summer.
SEPTEMBER
23 RD-- Autumn in the northern hemisphere and spring in the southern
hemisphere.
DECEMBER
21 ST -- The south pole is tilted towards the sun it is summer in the
southern hemisphere.
WATCH:
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| Fashion Watches Quartz Watches Wrist Watches Lady's Watches Jewelry Watches. |
A quartz
digital watch keeps time by counting the atomic vibrations of small quartz
crystal. In watches and small clocks the pendulam is replaced by a hairspring .
This makes a balance wheel is kept in the motion by the impulse it receives
from the mainspring through the escape wheel.
VELOCITY
AND ACCELERATION:
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| Velocity and Acceleration Page in my Physics-World Software |
Imagine
two towns that are 60 miles apart. Two cars drive the distance between these
towns.One goes all the way at 60 miles per hour (mph) and the other goes at 30
mph.Obviously the one that travels faster will get there more quickly.
VELOCITY:
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| Car Velocity |
When we
say that a car moves at 60 mph we mean that it takes it one hour to travel a
distance of 60 miles.Therefore it its get from one town to the other in one
hour.The second car only travels at 30 mph so that in one hour it has gone 30
miles so that in one hour it has gone 30 miles .Its take 2 hours to go the 60
miles .We said that the speed or velocity of the first car is greater than that
of the second car. In one hour the first car travels 60 miles whereas the
second car only travels 30 miles.Velocity measures the distance that some thing
moves in a certain times, or how fast it moves.Besides miles per hour velocity
is also measured in metres per second or kilometres per hour.
It is
quite easy to work out how fast something moves.If a car travels 100 miles in 4
hours how far does it travel in one hour? The answer is 100 divided by 4
(100/4) , or 25 miles.In other words the car`s velocity is 25mph.
Next time
you travel by car you can work out the average speed for the journey.Find out
from the mileometer how far you have travelled.Velocity is equal to distance
divided by time,so divide this distance by the length of time you have been
travelling. A motorway journey of 110 miles may take 2 hours.The average speed
is 55mph.For a town journey you may only go 20 miles in 1 hour so your velocity
is 20 mph.
Look at
the speedometer during this journeys. Sometimes it may read 60 mph,sometimes 30
mph . It may even read 0 mph when you are stuck in a traffick jam.This is
because the speed of a car changing all the time .The speedometer shows how
fast the car is moving at any point.The speed of a car over a whole journey is
the average speed.
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| Various Speed of Different Cars |
Average
velocity is:
s
v =
-----
t
(here v =
velocity, s = distance covered by an object,
t = time taken to cover the distance)
ACCELERATION:
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| Velocity and Acceleration |
When a
car is standing still it does not have any velocity at all. As it starts to
move it goes faster and faster.This is called acceleretion.If a car goe from 0
miles per hour to 50 miles per hour it has accelereted.A racing car can move
from 0 miles per hour to 50 mph very quickly . An old car may take much longer
to reach this speed.The racing car has more acceleretion.Acceleretion is the
rate at which something changes its speed.The opposite of acceleretion is
called deceleration-the rate of slowing down. If we assume that an moving
object at time t0 present at A point where its velocity is v0 then at the time
t moving object present at B point where it velocity is v then the average
acceleration of an object is:
v - v0
f =
----------------
t - t0
HI-SPEED
CARS:
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| High Speed Racing Car |
Most
ordinary car can reach a speed of between 70 and 100 mph , but cars powered by
jet engines can go much faster.In the 1983 the British driver Richard Noble
raised the world land speed 633.4 mph .
ANIMAL
SPEED:
Animals
show wide difference in the speeds at which they can travel .A snail can move
at about 1 millimetre per second(3.9 yard per hour). The fastest land animal is
the Cheetah which has been known to move at 26 metres per second (60 mph) over
short distance. A race horse can gallop 40 mph. The fastest speed ever measured
for a man running was almost 27 mph.
RELATIVE
VELOCITY:
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| Picture of Relative Velocity among the A, B , C cars |
Two car
named A and B coming to each other from opposite direction at a velocity of 50
km/hr and 60 km/hr respectively.In respect of A and B car`s drivers, both of
them assume that other car is more faster than his car. In this instance one
car`s driver assume that other car
coming toward his car in a velocity of 50 km/hr + 60 km/hr = 110 km/hr .
This is (110 km/hr) the relative velocity in respect of each A and B car. If
another car name C come into velocity of 70 km/hr in the same direction of car
A (50 km/hr) and overtake it . After this incident driver of A car assume that
car C come into very slow velocity of 70 km/hr - 50 km/hr = 20 km/hr and move in front of the car A .
Driver of car C assume that car A move backward at a velocity of 20 km/hr.
WEIGHT:
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| Weight Page in my Physics-World Software |
Pick up a
brick in one hand and block of wood of about the same size in the other. The
brick will feel heavier.It has more weight than the wood. The earth is pulling
the brick with a larger force.It does this because the brick has more mass than
the block of wood.In other words the
total amount of matter in the brick is greater than in the wood. We can see and
feel that different materials have different masses even if they are the same
size.The mass of a cube of gold would be nearly 20 times the mass of an ice
cube of the same size.
3D Animation Showing the Use of Weight Scale
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| Weighing Scale |
DENSITY:
The
lightness or heaviness of a substance for a given volume is called density.It
depends on how tightly the molecules in the substance are packed.
We say
that brick has greater density than wood .The stony particles of brick are
heavy nad are packed more tightly than the fibres of wood.
Imagine a
lift. When the lift is empty, its density is low. As the lift begins to fill with
people its density increases until it is full.It is then that its density is
greatest. Its size has remained the same throughout but its mass has increased.
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| Different affects of water density on Different Materials |
Density
is the mass of a certain volume of material.If a cube is 1 cm by 1 centimetre(1
cm3) . 1 cm3 of water weighs 1 gram.We say
its density is 11.3 g per cm3 .The
molecules of air are not very tightly packed and so its density is very low
,about 0.0012g per cm3.
Imagine a
peice of material to be made up of little cubes of the same size.If you know
how many of these cubes there are and weight of just one of them .You can work
out the weight of the piece.The number of small 1 centimetre cubes is the total
volume of the piece.
Equal
weights of different material may have different volume.If you have a pair of
old balance scales,put an iron kilogram weight on one side .Measure a kilogram
of sugar on the other.You can see that a kilogram of sugar has a much larger
volume than 1 kg of iron .This is because sugar has amuch lower density than
iron. Measure Kilograms of other materials and see how their volumes vary .The
smaller the volume for a given weight ,The greater the density.
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| Steel ships have an overall density of less than 1 kg per cm3 because their inside contain so much air.They can therefore float in water |
Materials
less dense than water can float.Icebergs which have a density less than that of
water can float in it.Steel ships have an overall density of less than 1 kg per
cm3 because their inside contain so much air.They can therefore float
in water. A peice of solid steel does not float .A peice of solid steel does
not float.People are about the same density as water so they can float or swim
without sinking.
The
density of a material is very important.We would not want to use a very dense
material to make an aeroplane because it would make the plane too heavy.So an
alloy , or mixture of metals is used The alloy consists mainly of mainly of
aluminum because it is not very dense.Other metals in this mixture give it
strength.Model aeroplanes are made up of balsa wood which also has very low
density.Lead is used as the sinker on the end of a fishing line because it is
very dense.
SINK &
FLOAT:
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| Sink and Float |
Some
materials sink in water because their densities are greater than the density
than water.Others will float . This shows that they are less dense than water.
Weight some objects that look the same size ,if they have different weights
then they have different densities.
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