Chapter 1 – Units and Dimensions

Dimensions: Dimensions are the basic concepts of measurement. Ex; such as length, time, T, P, etc.

Units: Units are means of expressing the dimensions.

       Dimensions à Force    Length         Time

                  Units à N          m, ft, cm,     h, min, s,

Basic Units: Units dimensionally independent, used for only one dimension. Ex; kg for mass, s for time,

Derived Units: Derived units are combination of various dimensions.

            Ex; in SI; Pressure: kg/m.s2   Pa(Pascal)

            density: kg/m3, heat capacity: Btu/1bm   ºF

System

B.E

A.E

cgs

M.K.S.

S.I.

Length

foot

foot

cm

m

m

Mass

slug

Ibm

g

kg

kg

Time

second

s

s

s

s

Temp

ºF

ºF

ºC

ºC

ºK

Heat

Btu

Btu

Cal

Kcal

Kcal

Force

Ibf

Ibf

dyne

Newton

N

Amount of Substance

Ibmole

Ibmole

g mole

kg mole

kg mole

   454 g = 1 Ibm       2.54 cm = 1 in       1 ft = 12 in

   (Ib ; pound)   (Btu; British thermal units)

 

Conversion of Units

Ex: Convert 20 gal/h to m3/s.

7.48 gal = 1 ft3        1 h = 3600 s        1 ft = 12 in

35.31 ft3 = 1 m3      1 in = 2.54 cm     1 m = 100 cm

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