The student is cautioned to always check the units  in any equation  written  for a  prob- lem solution, whether in school or in professional practice  after  graduation.  If properly written, an equation should  cancel  all units  across  the equal  sign.  If it does  not,  then you can be absolutely  sure  it is incorrect.  Unfortunately,  a unit  balance  in an  equation  does not guarantee  that  it is correct,  as many  other  errors  are  possible.  Always  double-check your  results.   You might  save  a  life.

1.11 WHAT'S TO COME

In this text we will explore the topic of machine design in respect to the synthesis of mechanisms in  order  to  accomplish   desired   motions   or  tasks,  and  also  the  analysis of these   mechanisms    in  order   to  determine   their  rigid-body    dynamic  behavior. On  the premise that we cannot analyze anything  until  it has  been  synthesized  into  existence,  we will  first  explore   the  topic  of  synthesis   of  mechanisms. Then  we  will  investigate   the analysis  of those  and  other  mechanisms  for  their  kinematic  behavior.  Finally,  in Part  II we will deal with the  dynamic  analysis  of  the  forces  and  torques  generated  by these moving machines. These topics cover  the essence  of the  early  stages  of a design  project. Once the kinematics and kinetics  of a design  have  been  determined,  most  of the  concep- tual  design  will  have  been  accomplished.    What  then  remains  is detailed   design-sizing the parts against failure. The topic of detailed design is discussed in other texts such  as reference   [8].

INTRODUCTION

Vorioble

Force Length Time Mass Weight Velocity

Acceleration Jerk

Angle Angle

Base Units in Boldface —  Abbreviations  in (  )

Symbol ips unit

£ pounds (lb)

/ inches (in)

/ seconds   (sec)

lb—sec2 / in (bl)

W pounds   (lb)

lps unit

pounds (lb) feet (ft) seconds (sec) lb—sec 2 / ( ) pounds (lb)

ft / sec

« / sec2 ft / sec!

degrees (deg) radians (rad)

m / sec! degrees (deg) radians (rad)

Angular veloci Angular acceleration Angular jerk

Torque

Mass moment of inertia Energy

Power Volume

Weight density Mass density

rad / sec

rad / sec! rad / sec 3 lb—ft lb—ft—sec 2 ft—lb

ft—lb / sec ft3

lb / It’ sI / It'

rad / sec rad / sec 2 rad / sec! N—m

N—in—sec! joules watts

REFERENCES

de Jonge, A. E. R. (1942). “What Is Wrong with ‘Kinematics’ and ‘Mechanisms’?”

Mechanical Engineering, 64(April), pp. 273-278.