note unit1.1
TRANSCRIPT
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DF014PHYSICS
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UNIT 1Physical Quantities
and Measurements1.1 Physical Quantities & Units
1.2 Scalars & Vectors
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1.1
Physical Quantities andUnits
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Learning Outcomes
At the end of this topic, students shouldbe able to:
State basic quantities and their respective SI
units State derived quantities (in terms of basic
quantities) and their respective units andsymbols
Perform conversion between SI units.
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1.1.aPHYSICALQUANTITY Category
Definition
Measured quantity
Basicquantity
Derived
quantity
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Definition:quantity which can be
- observed- measured
2 components:-Basic Quantity-Derived Quantity
PHYSICALQUANTITY
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BASIC QUANTITY
Definition
Quantity Quantitys Symbol
Length l
Mass m
Time t
Temperature T
Electric current I
Amount of substance n
Luminous Intensity Iv
Table 1
which cannot be derived from any
physical quantities.
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DERIVED QUANTITY
Definition
FormulaQuantitys
SymbolDerived Quantity
Fs cosWWork
maFForce
mvpMomentum
m
V
Density
v
t
aAcceleration
eg : (l) (w) (t)VVolume
s
t
vVelocity
Table 2
A physical quantity which can beexpressed in term of base quantity.
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1.1.bUNITS
Category
Definitionstandard size ofmeasurement
of physical quantities.
Base unit
Derived unit
S.I unit
Unitprefixes
Conversionof units
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Definition
standard size of measurement ofphysical quantities.
The common system of units used today :
- S.I unit(System International/metric system)
- cgs unit - UK.
The unit of base quantity is base unit
The unit of derived quantity is derived unit
UNITS
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QuantityQuantitys
SymbolSI Unit
Units
Symbol
Length l meter m
Mass m kilogram kg
Time t second s
Temperature T kelvin K
Electric current I ampere A
Amount of
substancen mole mol
Luminous
IntensityIv candela cd
Base unit
Table 3
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Derived unit
Derived QuantityQuantitys
Symbol
Formula Derived Unit
Velocity v s
t
m s-1
Volume V eg : (l) (w) (t) m3
Acceleration a vt
m s-2
Density m
V
kg m-3
Momentum p mv kg m s-1
Force F ma kg m s-2 @ N
Work W Fs cos kg m2 s-2 @ J
Table 4
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Used for presenting larger and smaller
value.
Example : How to write the readings
below by using unit prefixes?
1. 0.00000000145 m
2. 1234567 g
3. 5000000000 A
4. 1500000000000 J
5. 0.0768921 N
Unit Prefixes
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Prefix Value Symbol
tera x 1012 Tgiga x 109 G
mega x 106 M
kilo x 103 k
deci x 10-1 d
centi x 10-2 c
milli x 10-3 m
micro x 10-6 nano x 10-9 n
pico x 10-12 p
Unit Prefixes
Table 5
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Examples
Change 58000 m to km ????
1 m = 1000 km
58000 m = 58000 (x 10-3 km)
= 58 km
Presents 0.000009 s with unit prefixes.
0.000009 s = 9 x 10-6
s (10-6
= micro = )=9 s
Exercise:
Change a) 1 cm2 to m2b) 360 km h-1to m s-1
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2 2
2 -2 2
2 -4 -2
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3
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SOLUTIONS :
a) 1 cm ? m
1 (cm) = 1 (10 m)
1 cm = 10 m
b) 360 km h ?m s
360(km) 360(10 m)=
(h) (3600s)
= 100 m s
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S.I Units(system international)
The common system of unit
Use in base and derived unit- see Table 3 and Table 4
Also can be written in equivalent units.- see Table 6
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Physicalquantity S.I Units EquivalentUnitsUnits
Symbol
Pressure kg m-1 s-2 pascal Pa
Force kg m s-2 newton N
Power kg m2 s-3 watt W
Work kg m2 s-2 joule J
Frequency s-1 hertz Hz
**Sometimes when we use certain instruments tomeasure physical quantity, the measurement isnot in SI unit.
Examples for Equivalent Units
Table 5
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Examples of unit conversion :
3
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3 -3 3 -9 3
-3
-3 3 -3
-2 3
(10 m)a) 15 km h =15 = 4.17 m s(6060 s)
b) 5 mm = 5(10 m) = 510 m
10 kgc) 7 g cm = 7 = 710 kg m
(10 m)
d) 30 C = 30 + 273 = 303 K