2. 1M! design of thiS fOC~et and gant:)' structure requires 11
basIc ~nowledge of both statics and dynamiCS. which form the
subject matter of engineering mechanil::s.
3. General Principles CHAPTER OBJECTIVES To provide an
introduction to the basic quantities and idealizations of me A and
8 arc W/lill((lf, i.e.. bolh h:l'c the lI:lmc line of aClion. the
parallelogram law reduces 10 an /I/g~b",ir or l"CI,llIr mltfirioll
R = A + 8. as shown in fig. 2-5. :. , Addillon of rolti JC~' '"tOB
Fig. 2- 5 Vector Subtraction. The resultant of the tfiffrrmCl'
between Iwo VCC;[ors A and nof lhe same I)'PC may be expressed as
R' = A - II = A + (-8 ) This vtClor sum is shown graphically in
Fig. 2-6. Subtraction is therefore defined as 11 special case of
addition. so the rules of "CClor addition also apply 10 vector
subtract;oll. I 2.2 VECtOR OPRATlONS Triangle OOIImunioo '9
19. 20 CH"'PfE~ 2 FORCE VECTORS The p~talkloglam bw muse he
used.o determine .he rcsullall'
20. 2.3 V{CTOR AOOl110N 01' FO!tCs " , """""-------" ", ,>,
Addition of Several Forces. If more than twO forces arc to be
added. successive applications of the parallelogmm law can be
carried out in ordt'r to obtain the resultant force. For example.
if three forces Fl' ."2. FJ act at a point 0, Hg. 2-9. the
resultant of any IWOof the forces is found. say. + F!-:lIId then
this resultant is added to the third (orce. yielding the resultant
of all three forces: i.e.. "If = (Fl + F2)+FJ. Using the
parallelogram law 10 add morc Ihan t.....o forces. as shown here.
oflen requires extensive geometric and trigonometric c:deulalion 10
determine Ihe numeric..l ' ~Iues for the magnitude and direction of
the result~nl. InSlead, problems of Chis type are easily solved by
using lhe "reCltlOgular- component method." which is e.~plained in
Sec. 2.4. "b~ r~suhan1 fore
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