01 Physical Quantity

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Physical

QuantityA quantity that can be

measured and consists of anumerical magnitude and a unit.

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Physical Quantity

Base

Quantity

Derived

Quantity

A unit that is not

combined with one

another or more

physical quantities.

A combination of two

or more base

quantities.

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Base Quantities

BaseQuantity

Symbol SI UnitSymbol for

the unit

Length l Metre m

Mass m Kilogram kg

Time t Second s

Temperature T Kelvin KElectrical

current I ampere A

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Derived Quantity

A combination of two or more base quantities.

Physical

quantitySymbol Relation with base quantity Formula SI units

Volume V Length (m) X Length (m) X Length(m) V = l3 m3

Velocity v Displacement (m) / Time (s) v = s/t ms -1

Density Mass (kg) / Volume (m3) = m/V kg m-3

Force F Mass (kg) X Acceleration (m s-2) F = ma N

Electric

charge Q Current (ampere) X time (s) Q = It C

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The values of measurement in scientific

studies normally involve numbers that areeither very large or very small.

Such number are difficult to record or to

read off.

Speed of light:

=300 000 000 ms-1

The distance between the Sun and Mars

=227 800 000 000 m

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Scientific Notation

The form in the scientific notation is

nM 10

1300000000

ms8

103

m320000000000.011

102.3

Standard form

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Prefixes

Prefixes are used in the metric system toindicate fractions or multiples of SI units.

For measurement whose magnitude isvery large, prefixes such as kilo, Mega,

Giga and Tera are used.

For measurement whose magnitude is

very small, prefixes such as centi, milli,

micro, nano and pico are used.

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Prefixes

Prefix Symbol Standard Form Example

Tera- T 1012 Terametre (Tm)

Giga- G 109 Gigabyte (GB)

Mega- M 106 Megawatt (MW)

kilo- k 103 Kilometre (km)

hecto- h 102 Hectometre (hm)

deka- da 101 Dekametre (da m)

deci- d 10-1 Decimetre (dm)

centi- c 10-2 Centimetre (cm)

milli- m 10-3 Milligram (mg)

micro- 10-6 Microwatt (W)

nano- n 10-9 Nanosecond (ns)

pico- p 10-12 Picometre (pm)

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Complete the following:

Quantity StandardForm

Prefixes Form

(a) 28 000 000 000

bytes

Megabytes

(b) 3675 000g kg

(c) 0.000 000 24s s

(d) 0.000000031 8m cm

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2. Convert each of the following measurements

into metres, m.

(a)1.55 X 10 -1 Tm

(b)1.55 X 10-3 Mm

(c)1.55 X 10-3 dm

(d)1.55 X 104m

(e)1.55 X 10 pm

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Scalar

Quantity

Vector

Quantity

Physical quantity

that has magnitude

but no direction

Physical quantity

that has magnitude

and direction

Physical

Quantity

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ScalarQuantity

VectorQuantity

Examples:

LengthMass

Time

temperature

DisplacementWeight

Velocity

Acceleration

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20N

30N

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20N

50N

30N

Resultant force