Page 14 - Thomson, William Tyrrell-Theory of Vibration with Applications-Taylor _ Francis (2010)

The SI System

of Units

THE SI SYSTEM OF UNITS

The English system of units that has dominated the United States from historical
times is now being replaced by the SI system of units. Major industries throughout
the United States either have already made, or are in the process of making, the
transition, and engineering students and teachers must deal with the new SI units
as well as the present English system. We present here a short discussion of the SI
units as they apply to the vibration field and outline a simple procedure to convert
from one set of units to the other.
The basic units of the SI system are

Units Name Symbol
Length Meter m
Mass Kilogram kg
Time Second s
The following quantities pertinent to the vibration field are derived from
basic units:
Force Newton N ( = kg • m/s^)
Stress Pascal P a(= N/m^)
Work Joule J (= N • m)
Power Watt W (= J/s)
Frequency Hertz H z(= 1/s)
Moment of a force N • m (= kg • mVs^)
Acceleration m/s^
Velocity m /s
Angular velocity 1/s
Moment of inertia (area) X
Moment of inertia (mass) kg • (kg • cm^ x 10““*)