182. Bosch Automotive Handbook-Bentley Publishers.pdf

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Electronic

Automotive Handbook

1. Edition

Choose a chapter in the table of contents

or start with the first page.

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Basic principles, Physics

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Basic principles, Physics

Quantities and units

SI units

SI denotes "Système International d'Unités" (International System of Units). The

system is laid down in ISO 31 and ISO 1000 (ISO: International Organization for

Standardization) and for Germany in DIN 1301 (DIN: Deutsches Institut für Normung

– German Institute for Standardization).

SI units comprise the seven base SI units and coherent units derived from these

base Sl units using a numerical factor of 1.

Base SI units

Base quantity and symbols

Base SI unit

Name

Symbol

Length

meter

Mass

kilogram

Time

second

Electric current

ampere

Thermodynamic temperature

kelvin

Amount of substance

mole

mol

Luminous intensity

candela

All other quantities and units are derived from the base quantities and base units.

The international unit of force is thus obtained by applying Newton's Law:

force = mass x acceleration

where m = 1 kg and a = 1 m/s 2 , thus F = 1 kg · 1 m/s 2 = 1 kg · m/s 2 = 1 N (newton).

Definitions of the base Sl units

1 meter is defined as the distance which light travels in a vacuum in 1/299,792,458

seconds (17 th CGPM, 1983 1 ). The meter is therefore defined using the speed of light

in a vacuum, c = 299,792,458 m/s, and no longer by the wavelength of the radiation

emitted by the krypton nuclide 86 Kr. The meter was originally defined as the forty-

millionth part of a terrestrial meridian (standard meter, Paris, 1875).

1 kilogram is the mass of the international prototype kilogram (1 st CGPM, 1889 and

3 rd CGPM, 1901 1 ).

1 second is defined as the duration of 9,192,631,770 periods of the radiation

corresponding to the transition between the two hyperfine levels of the ground state

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Basic principles, Physics

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of atoms of the 133 Cs nuclide (13 th CGPM, 1967. 1 )

1 ampere is defined as that constant electric current which, if maintained in two

straight parallel conductors of infinite length, of negligible circular cross-sections,

and placed 1 meter apart in a vacuum will produce between these conductors a

force equal to 2 · 10 –7 N per meter of length (9 th CGPM, 1948. 1 )

1 kelvin is defined as the fraction 1/273.16 of the thermodynamic temperature of the

triple point 2 ) of water (13 th CGPM, 1967. 1 )

1 mole is defined as the amount of substance of a system which contains as many

elementary entities as there are atoms in 0.012 kilogram of the carbon nuclide 12 C.

When the mole is used, the elementary entities must be specified and may be

atoms, molecules, ions, electrons, other particles, or specified groups of such

particles (14 th CGPM 1 ), 1971.

1 candela is the luminous intensity in a given direction of a source which emits

monochromatic radiation of frequency 540 x 1012 hertz and of which the radiant

intensity in that direction is 1/683 watt per steradian (16 th CGPM, 1979. 1 )

1 ) CGPM: Conférence Générale des Poids et Mesures (General Conference on Weights and

Measures).

2 ) Fixed point on the international temperature scale. The triple point is the only point at which

all three phases of water (solid, liquid and gaseous) are in equilibrium (at a pressure of

1013.25 hPa). This temperature of 273.16 K is 0.01 K above the freezing point of water

(273.15 K).

Decimal multiples and fractions of Sl units

Decimal multiples and fractions of SI units are denoted by prefixes before the name

of the unit or prefix symbols before the unit symbol. The prefix symbol is placed

immediately in front of the unit symbol to form a coherent unit, such as the milligram

(mg). Multiple prefixes, such as microkilogram ( Ⱥ kg), may not be used.

Prefixes are not to be used before the units angular degree, minute and second, the

time units minute, hour, day and year, and the temperature unit degree Celsius.

Prefix

Prefix symbol

Power of ten

Name

atto

10 –18

trillionth

femto

10 –15

thousand billionth

pico

10 –12

billionth

nano

10 –9

thousand millionth

micro Ⱥ

10 –6

millionth

milli

10 –3

thousandth

centi

10 –2

hundredth

deci

10 –1

tenth

deca

10 1

ten

hecto

10 2

hundred

kilo

10 3

thousand

mega

10 6

million

giga

10 9

milliard 1 )

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Basic principles, Physics

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tera

10 12

billion 1 )

peta

10 15

thousand billion

exa

10 18

trillion

1 ) In the USA: 10 9 = 1 billion, 10 12 = 1 trillion.

Legal units

The Law on Units in Metrology of 2 July 1969 and the related implementing order of

26 June 1970 specify the use of "Legal units" in business and official transactions in

Germany. 2 )

Legal units are

the SI units,

decimal multiples and submultiples of the SI units,

other permitted units; see the tables on the following pages.

Legal units are used in the Bosch Automotive Handbook. In many sections, values

are also given in units of the technical system of units (e.g. in parentheses) to the

extent considered necessary.

2 ) Also valid: "Gesetz zur Änderung des Gesetzes über Einheiten im Meßwesen" dated 6 July

1973; "Verordnung zur Änderung der Ausführungsverordnung" dated 27 November 1973;

"Zweite Verordnung zur Änderung der Ausführungsverordnung" dated 12 December 1977.

Systems of units not to be used

The physical system of units

Like the SI system of units, the physical system of units used the base quantities

length, mass and time. However, the base units used for these quantities were the

centimeter (cm), gram (g), and second (s) (CGS System).

The technical system of units

The technical system of units used the following base quantities and base units:

Base quantity

Base unit

Name

Symbol

Length

meter

Force

kilopond

Time

second

Newton's Law,

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