# International System of Units (SI)

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International System of Units (SI)

Common system of units for use in the communication of data. It is a precise and unambiguous system for the description of a large number of physical and chemical properties.

Base Units:
1) Metre (length)
2) Kilogram (mass)
3) Second (time)
4) Ampere (electric current)
5) Kelvin (temperature)
6) Mole (amount of substance)
7) Candela (luminous intensity)
All other units are derived from these quantities.

Units commonly used in biomechanics:
Linear velocity (speed)  metre per second (m/s)
Linear acceleration  metre per second squared (m/s2)
Moment of inertia  kilogram metre squared (kg.m2)
Density  kilogram per cubic metre (kg/m3)
Force  Newton (N), (kg.m/s2)
Moment of force (torque)  Newton metre (N.m)
Pressure, stress  Pascal (Pa), (N/m2)
Energy, work  joule (J), (kg.m2/s2)
Power  watt (W), (J/s)
Linear momentum  Newton second (N.s or kg.m/s)

Prefixes:
1 000 000 000 109 giga G
1 000 000 106 mega M
1 000 103 kilo k
100 102 hecto h
10 101 deca da
0.1 10-1 deci d
0.01 10-2 centi c
0.001 10-3 milli m
0.000 001 10-6 micro μ
0.000 000 001 10-9 nano n