MEASUREMENT
MEASUREMENT
Measurement
is the determination of the
dimensions,quantity or capacity of an item.
To measure physical quantities such as
mass,time,length etc we use UNITS.
A unit is a fixed quantity used as a standard for
measurement.
Fundamental Quantities
Derived Quantities
The physical quantities
which do not depend upon
other quantities are called
fundamental quantities.
Fundamental quantities are
mass, length, time,
temperature, luminous
intensity, current and
amount of substance
Units of physical quantities
which may be derived from
fundamental units are called
derived units.
Unit of area( area = length
× breadth) Unit of
Velocity(displacement/time)
Systems of Units :
There are following principle system of
units:
 C.G.S System : length ? centimeter (cm),
mass ? gram (g) time ? second (s).
 F.P.S System : length ? foot (ft), mass ?
pound (lb), time ? second (s).
 M.K.S. System: length ? meter (m), mass ?
kilogram (kg), time ? second (s)
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SI UNITS…
MASS
Mass of a body is defined as the quantity
of matter in the body.
 We express mass of an object in gram (g)
kilogram (kg) , tonne , quintal etc
 The SI unit of mass is kilogram.
 Mass of an object does not change from
place to place.
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UNITS OF MASS
Some of the commonly used units of mass
and conversions are :
 1 tonne = 10 quintal
 1 quintal = 100 kg
 1 kg = 1000 g
 1 g = 1000 mg
Measurement of mass
Beam balance
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A beam balance consists of a horizontal beam ,
supported at its centre.
Two pans of equal masses are suspended from both the
ends of the beam.
The object is kept on one pan and the standard masses
on the other.
When both the pans are equally loaded , the beam is
horizontal and the pointer points vertically up at the
center.
Physical balance
Physical balance
Physical balances are utilized for precision
mass measurement .
 A physical balance can measure accurately
upto a milligram.
 It is provided with a box of standard
masses ranging from 1mg to 100g.
 It works on the same principle as that of
a beam balance.
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WEIGHT
Weight is the force exerted on a body by
gravity.
 This is often expressed in the formula
W = mg, where W is the weight, m the
mass of the object, and g gravitational
acceleration
 The SI unit of weight is Newton(N)
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Measurement of weight
Spring balance
Measurement of weight
A spring balance is used to measure
weight of a body
 It consists of a spring fixed with a pointer
at the upper part and a hook at the lower
end to suspend the body
 The extension produced in a spring is
directly proportional to the gravitational
force acting on it.
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Comparison between mass and
weight
MASS
Amount of matter present
in the body
SI unit is kg
Measured using a beam
balance
Does not vary with place
WEIGHT
Gravitational force on a
body
SI unit is Newton (N)
Measured using a spring
balance
Weight varies with place
DENSITY
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The density of a material is its mass per
unit volume.
The symbol most often used for density is ρ
(the lower case Greek letter rho).
ρ =m/V
where ρ is the density, m is the mass, and V
is the volume.
The SI unit of density is kg/m3
Density of different substances
Question???
Equal masses of iron and common salt
have different volumes.
Determining the density of a
irregular solid
For an irregular solid like a stone, volume
can be found using a graduated measuring
cylinder.
 The measuring cylinder is half filled with
water and the initial water level is noted
 Then the stone is immersed in water with
the help of a thread and the reading of
the water level is noted
 The mass of the stone is determined
using a physical balance
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Thus the density of the stone is found using
formula
D=M/(Final volume-Initial volume)
RELATIVE DENSITY
Relative density, or specific gravity, is
the ratio of the density (mass of a unit
volume) of a substance to the density of a
given reference material.
 It tells us how dense or heavy is the
density of a substance with respect to
water
 Relative density has no units
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Measurement of relative density of a
liquid
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The relative density of a liquid can be
determined with the help of a relative
density bottle
Relative density bottle
It is a small, thin walled glass bottle with a
stopper having a fine hole.
 The mass( m1 ) of the empty bottle is
determined using a physical balance.
 The liquid whose density is to be
measured is filled into the bottle and its
mass( m2 ) is determined.
 Now clean the bottle thoroughly and find
the mass of bottle when it is filled with
water(m2 )
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Calculating RD
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RD=Density of liquid
Density of water
=Mass of liquid/Volume of liquid
Mass of water/Volume of water
= (m2 – m1 ) / (m3 – m1 )
Practical application of relative
density
Looking at the RD of different substances
we can find whether an object or a liquid
sinks or floats in water.
 If a substance‘s RD is less than one it
floats in water.
 If a substance‘s RD is more than one it
sinks in water.
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HYDROMETER
Hydrometer is a device designed to float
on a liquid
 There are special hydrometers for liquids
lighter and denser than water, for testing
the purity of milk, for testing the
concentration of acids in batteries.
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Reference
http://www.convertunits.com/
 http://www.easyunitconverter.com/
(conversion)
 http://www.aasd.k12.wi.us/staff/boldtkathe
rine/MathResources36/Math_Measurement.htm#LENGTH
(interactive)
 http://www.syvum.com/cgi/online/serve.cg
i/squizzes/physics/measure1.tdf?0 (quiz)
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