Page 21 - Aerodynamics for Engineering Students

4 Aerodynamics for Engineering Students

Table 1.1 Units and dimensions

Quantity Dimension Unit (name and abbreviation)
Length L Metre (m)
Mass M Kilogram (kg)
Time T Second (s)
Temperature e Degree Celsius ("C), Kelvin (K)
Area L2 Square metre (m2)
Volume L3 Cubic metre (m3)
Speed LT-I Metres per second (m s-')
Acceleration LT-~ Metres per second per second (m s-*)
Angle 1 Radian or degree (")
(The radian is expressed as a ratio and is therefore
dimensionless)
Angular velocity T-l Radians per second (s-l)
Angular acceleration T-2 Radians per second per second (s-~)
Frequency T-I Cycles per second, Hertz (s-' Hz)
Density MLP3 Kilograms per cubic metre (kgm-3)
Force MLT-~ Newton (N)
Stress ML-~T-~ Newtons per square metre or Pascal (Nm-2 or Pa)
Strain 1 None (expressed as %)
Pressure ML-~T-~ Newtons per square metre or Pascal (N m-2 or Pa)
Energy work ML~T-~ Joule (J)
Power ML2TP3 Watt (W)
Moment ML~T-~ Newton metre (Nm)
Absolute viscosity ML-IT-I Kilogram per metre second or Poiseuille
(kgrn-ls-' or PI)
Kinematic viscosity L2T- Metre squared per second (m2 s-I)
Bulk elasticity ML-~T-~ Newtons per square metre or Pascal (Nm-2 or Pa)

1 .I .4 Imperial unitss
Until about 1968, aeronautical engineers in some parts of the world, the United
Kingdom in particular, used a set of units based on the Imperial set of units. In this
system, the fundamental units were:
mass - the slug
length - the foot
time - the second
temperature - the degree Centigrade or Kelvin.

1.2 Relevant properties

1.2.1 Forms of matter
Matter may exist in three principal forms, solid, liquid or gas, corresponding in that
order to decreasing rigidity of the bonds between the molecules of which the matter is
composed. A special form of a gas, known as a plasma, has properties different from

Since many valuable texts and papers exist using those units, this book contains, as Appendix 4, a table of
factors for converting from the Imperial system to the SI system.