Units


Units framework

The BIPM manages the International System of Units (SI ) wherein seven base units have been defined, from which all other units can be derived :

SI Base units
Quantity Dimension Base unit
Name Symbol
Time T second s
Length L metre m
Mass M kilogram kg
Electric current I ampere A
Temperature Θ kelvin K
Amount of substance N mole mol
Luminous intensity J candela cd
Unit multiples
Multiple Fraction
Factor Name Symbol Factor Name Symbol
1024 yotta Y 10-24 yocto y
1021 zetta Z 10-21 zepto z
1018 exa E 10-18 atto a
1015 quadrillion peta P 10-15 femto f
1012 trillion tera T 10-12 pico p
109 billion giga G 10-9 nano n
106 million mega M 10-6 micro μ
103 thousand kilo k 10-3 milli m
102 hundred hecto h 10-2 centi c
101 ten deca da 10-1 deci d

Kinetic energy

Kinetic energy
Quantity Definition Unit Formula
Velocity Rate of change of on object's position in function of time.
Speed is the scalar absolute value (magnitude) of velocity.		 m/s
Acceleration Rate of change of the velocity of an object with respect to time. m/s2
Force A force causes an object with mass to accelerate. newton N \( N = kg \space m \space s^{-2} \)
Weight Force acting on the object due to gravity.
The Earth's gravitational accelaration (free fall in a vacuum) has a conventional standard value of 9.80665 m/s2, the effective one however depending on latitude and altitude.		 newton N \( W = F_g = m \space g = 9.80665 N \)
Energy Work required to move a force over a distance. joule J \( J = N m = kg \space m^2 \space s^{-2} \)

Electricity

Electricital energy
Quantity Definition Unit Formula
Charge Physical property of matter that causes it to experience a force when placed in an electromagnetic field. Corresponds to the electric mass. coulomb C
Current Stream of charged particles moving through an electrical conductor. It expresses the intensity of the electric flux. ampere A \( A = C \space s^{-1} \)
Potential difference The electric potential energy per unit charge. Pressure of the electric flow or electromotive force. volt V \( V = J \space C^{-1} \)
Power Amount of energy transferred or converted per unit of time. The rate at which electrical work is performed when a current flows across an electrical potential difference. watt W \( W = V \space A = J \space s^{-1} \)
Energy Electrical work performed when a current flows across an electrical potential difference during some elapsed time. joule J \( J = W \space s = C \space V \)

Units of measure

Units of measure