Table 8. 7 



FUNDAMENTAL AND DERIVED UNITS. 

 Conversion Factors. 



To change a quantity from one system of units to another: substitute in the corresponding 

 conversion factor from the following table the ratios of the magnitudes of the old units to the 

 new and multiply the old quantity by the resulting number. For example: to reduce velocity 

 in miles per hour to feet per second, the conversion factor is lt~^; I = 5280/1, t = 3600/1, and 

 the factor is 5280/3600 or 1.467. Or we may proceed as follows: e. g., to find the equivalent of 

 I c.g.s. unit of angular momentum in the pd.ft.m. unit, from the Table t g cm2/sec.=.r lb. ft-Vmin, 

 where x is the factor sought. Solving, 4r='ig/lb. X cmVft.^ X min./sec, = i X .002205 X .001076 

 X 60 = . 0001425. 



The dimensional formulae lack one quality which is needed for completeness, an indication of 

 their vector characteristics; such characteristics distinguish plane and solid angle, torque and 

 energy, illumination and brightness. 



(a) Fundamental Units. 

 The fundamental units and conversion factors in the systems of units most commonly used 

 are: Length [/]; Mass [w]; Time [/]; Temperature [&]; and for the electrostatic system, 

 Dielectric Constant [^]; for the electromagnetic system, Permeability [ju]. The formulae 

 will also be given for the International System of electric and magnetic units based on the units 

 length, resistance [r], current [i], and time. 



(b) Derived Units. 



Name of unit. 



(Geometrical and 

 dynamical.) 



Area, surface , 



Volume 



Angle , 



Solid angle 



Curvature 



Angular velocity 



Linear velocity 



Angular acceleration. . . 

 Linear acceleration 



Density 



Moment of inertia 



Intensity of attraction. 



Momentum 



Moment of momentum. 

 Angular momentum .... 



Force 



Moment of couple, 



torque 



Work, energy 



Power, activity 



Intensity of stress. . . . 

 Modulus of elasticity. 



Compressibility 



Resilience 



Viscosity , 



Name of units. 

 (Heat and light.) 



Quantity of heat: 



thermal units 



thermometric units. . 

 dynamical units .... 



Coefficient of thermal 

 expansion 



Thermal conductivity: 



thermal units 



thermometric units 



or diffusivity 



dynamical units .... 



Thermal capacity 



Latent heat: 



thermal units 



dynamical units .... 



Joule's equivalent 



Entropy: 

 heat in thermal units 

 heat in dynamical 

 units 



Luminous intensity.... 



Illumination 



Brightness 



Visibility 



Luminous efficiency. . . . 



Conversion 

 factor. 



o 

 2 

 o 



-2 



-2 

 -2 



O 

 -2 



— I 



-3 



o 



-2 



o 

 -I 



I* 



* For these formula the numbers in the last column are the exponents of F where F refers to the luminous flux 

 For definitions of these quantities see Table 299, page 259. 



Smithsonian Tables. 



