1 Introduction
© 2007 The McGraw-Hill Companies, Inc. All rights reserve.
 
© 2007 The McGraw-Hill Companies, Inc. All rights reserve.
 
the conditions of rest or motion of bodies under the
action of forces$
- Statics - (ynamics
" Mechanics is an applied science - it is not an abstract
or pure science but does not ha)e the empiricism
found in other en%ineerin% sciences$
" Mechanics is the foundation of most en%ineerin% sciences
and is an indispensable prere*uisite to their study$
 
© 2007 The McGraw-Hill Companies, Inc. All rights reserve.
 
Fundamental Concepts
" Space - associated #ith the notion of the position of a point P %i)en in
terms of three coordinates measured from a reference point or ori%in$
" Time - definition of an e)ent re*uires specification of the time and
 position at #hich it occurred$
"  Mass - used to characteri,e and compare bodies e$%$ response to
earth.s %ra)itational attraction and resistance to chan%es in translational
motion$
"  Force - represents the action of one body on another$ force is
characteri,ed by its point of application ma%nitude and direction i$e$
a force is a )ector *uantity$
/n Ne#tonian Mechanics space time and mass are absolute concepts
independent of each other$ Force ho#e)er is not independent of the
other three$ 0he force actin% on a body is related to the mass of the body
and the )ariation of its )elocity #ith time$
 
© 2007 The McGraw-Hill Companies, Inc. All rights reserve.
 
"  Newton’s First Law& /f the resultant force on a
 particle is ,ero the particle #ill remain at rest
or continue to mo)e in a strai%ht line$
"  Newton’s Third Law& 0he forces of action and
reaction bet#een t#o particles ha)e the same
ma%nitude and line of action #ith opposite
sense$
an acceleration proportional to a non,ero
resultant applied force$
22
 R
© 2007 The McGraw-Hill Companies, Inc. All rights reserve.
 
and force$
as basic #nits may be defined
arbitrarily$ 0he fourth unit referred
to as a derived #nit  must ha)e a
definition compatible #ith Ne#ton.s
2nd 4a#
am F  =
0he basic units are len%th time and
mass #hich are arbitrarily defined as the
meter 5m6 second 5s6 and 3ilo%ram
53%6$ Force is the deri)ed unit
( )        
   =
=
force #hich are arbitrarily defined as the
foot 5ft6 second 5s6 and pound 5lb6$
Mass is the deri)ed unit
sft1
© 2007 The McGraw-Hill Companies, Inc. All rights reserve.
 
#hat is to be determined and a fi%ure
sho#in% all *uantities in)ol)ed$
"  Free'(ody )iagrams&
the bodies in)ol)ed #ith a clear
indication of all forces actin% on
each body$
applied to e8press the conditions of
rest or motion of each body$ 0he
rules of al%ebra are applied to sol)e
the e*uations for the un3no#n
*uantities$
computed results are correct
substitutin% %i)en data and computed
results into pre)iously unused
-   always apply e8perience and physical
intuition to assess #hether results
seem 9reasonable:
© 2007 The McGraw-Hill Companies, Inc. All rights reserve.
 
"umerical Accuracy
" 0he accuracy of a solution depends on 16 accuracy of the %i)en
data and 26 accuracy of the computations performed$ 0he solution
cannot be more accurate than the less accurate of these t#o$
" s a %eneral rule for en%ineerin% problems the data are seldom
3no#n #ith an accuracy %reater than <$2=$ 0herefore it is usually
appropriate to record parameters be%innin% #ith 91: #ith four di%its
and #ith three di%its in all other cases i$e$ +<$2 lb and 1$; lb$
" 0he use of hand calculators and computers %enerally ma3es the
accuracy of the computations much %reater than the accuracy of the
data$ >ence the solution accuracy is usually limited by the data
accuracy$