UNITS

There are seven fundamental units in SI system

Energy has numerous form; such as heat, work, kinetic energy, potential energy, electric energy, chemical energy and atomic energy. All forms of energy are measured by Joule (1 J = 1 N.m)

The unit of any quantity is based on the definition of that quantity. As example is the specific heat, which is defined as the quantity of heat required to increase one kilogram of a substance by one degree Celsius.

Specific gravities of some substances at 0 oC

Viscosity is a property by virtue of which the fluid resists shear stressUnit of viscosity is determined based on Newton’s law of viscosity:

t = m du/dy which implies that: [m] = [t] / [du/dy] = Pa.sec = kg/m.s

Thermal conductivity is a property defined based Fourier law of heat conduction:

Q (Watt) = - k (W/m.K) A (m2) Dt (K)/Dx (m).

Convection heat transfer coefficient is defined based heat transfer by convection:

Q (Watt) = h (W/m2.K) A (m2) Dt (K).

Stefan-Boltzmann coefficient is defined based heat transfer coefficient by radiation:

Q (Watt) = s (W/m2.K4) . A (m2) . T14 T2

4) (K4)

The candela ( or ; symbol: cd) is the SI base unit of luminous intensity; that is, power emitted by a light source in a particular direction, weighted by the luminosity function (a standardized model of the sensitivity of the human eye to different wavelengths, also known as the luminous efficiency function). A common candle emits light with a luminous intensity of roughly one candela.

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( ) 540يساوي ) محددة شدة وعند ، هرتز مليون [...] 1/683مليون•] ) قياس ) وحدة ]Candelaشمعة

• • The candela ( or ; symbol: cd) is the SI base unit of luminous intensity; that

is, power emitted by a light source in a particular direction, weighted by the luminosity function (a standardized model of the sensitivity of the human eye to different wavelengths, also known as the luminous efficiency function). A common candle emits light with a luminous intensity of roughly one candela. If emission in some directions is blocked by an [...]