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Unformatted text preview: Chapterﬁ A force is a push er a puiir it is that which
causes an chject tn acceierate. The unit cf force
in the metric system is the Newtcn. Puree is a
vector quantim Every bcdy centinues in its state nf rest er cf
uniferm mntinn in a straight iine unless it is
cempeiieei by a fume tn change that state. The mass of an abject is that nrnperty that
speciﬁes hcw much resistance the Object
exhibits to changes in its veiccity (a measure cf
the inertia ef the ehject). Mass is a scaiar anantity, The unit cf mass in the metric systcrn
is the kiicgrarn. The net three 2? acting an an chjcct cf mass
“in” is cqnai tc the prcauct ni the chi cctﬁs mass with its acceieraticn ii. Read sections 13.1 and i339 Net’s Lew Grmiizee: Every particic (with ncnmzcrn mass) in the
universe attracts every ether particic {with itch
zcm mass) with a three that is directiy
prepcrticnai tn the prcanct of their masses ma
inversely prcpcrtienai t0 the square cf the distance between them That isg I???
nun2 b" i?! Z G 1.2 6/733; Where
G * 6.67Xm'“ NtrtZ/kg2 at» the universal gravitaticnal cchstaht.
r = distance from the center cf mass cf che
particle tn the center cf mass cf the ether particle. The attractive three exerted hy the Earth ch an
ehject is called the gravitationalfcrcc Pg. This three is called the weight ct” the cbj ect, and its
directicn is tc‘ward the center cf the Earth. The
weight of an abject of mass m on the Earth has a magnitude equal tc; Mﬁm
R 2 E gr g £26 The quantity G R: appears sc eften that it is given the name igi cr simply g. This quantity is
alsc called the gravitaticrzaiﬁeid generated by
the Earth at lccaticns near its sarface. The gravitatienai ﬁein g is a reefer quantity with a direerian teward the center at the Earth? and
with a magnitude nefmeé as M
W: 26%
is s R2 E nsing G : same“ NmZ/kg2 ME m 5698x1024 kg (mass nf the Earth) RE : 6.37Xmé m (radius efthe Earth) yieins a Value 0f g x 9.8 m/sZ. One can thus say
that the weight ef an abject ef mass m en the
surface nf the Earth is Egmrng Where g x the aeeeieratien dine tn gravity? aiways direeted inward the center ef the Earth.
New yen knew Where the 9.8 W32 mines frnnm H bedy “A” exerts a farce EB err hody “B”?
thee hedy “B” exerts arr equal: (magnitude) am
eppesite (directien) farce EA err bedy “A”. FAB : FBA Forces always occur in pairs. Censider a Meek of mass m sliding with a speed
v en a horizemsj surface. Let F he the net force
exertee by the herizerltai surfaee err the Neck. The hernia! tersea n9 is (leﬁneu as the
eemnenent ef the force F? that is nemenrtie‘ular
(er normal) tn the herizental surface. Theﬂicz‘iunal forcefis the cempenent 0f the
force F' that is parallel to the hurizontal surface. The are twe “kinds” of frictional fumes: {A} The Kinetie Frictiuual Furceﬁ (sliding) The magnitude 0f the frietiunal farce ﬂ: is
prepartional tn the magnitude ef the nermal a
farce. The eenstant 0f prepertienallty is human as the mefﬁciem usz’neticﬂictien ukt fix ttktt {AhWAY31 : The Statie Frietienal Fereefs the
slipging) The magnituue uf the frictienal three f; is relateu
tn the magnitude 0f the neaal three it. ﬁﬁwn its = the eeefﬁeient of static frietiens The equaiity Sign hams when the surfaces are an
the verge 9f siipping (impending mntien). The
inequality Sign heids when the surfaces are net
en the verge ef siipping. Objeets in Enniiihriunt:
An object is said to he in mechanical
eqniiihrium when twe canni‘tions are met: {a} The netfnree aeting an it is eqnai tn zeree This ensures transfaztenai enaitz’hriam.
Frern 2? n ma we see that if 2F 2 Q 3 then name ::.> t{Exemistant
That is, the abject is (i) at rest and stays at rest
er (ii) the ehj eet meves in a straight Tine with
eenstant veieeityi {h} The net terque aetihg es the ehjeet is zete. This ehsui‘es rammed eqmiz’brmm, Mere eh
this tepie when yth study ehaptet’ m (in
Physics 7B). Strategy fer appiying Newmn’s ans sf
metiem (a) iseiate (eensider) s pert ef the system or the
entire system and draw the threes acting ON its (b) Apply Newmh’s 2rid iaw 0f metien in
eempenem fem; (e) Ssh/e fee shy uttkﬁQth quantities {d} if the seeeierstieh ef the ehj eet is CﬁﬂSiai‘iig
then. we may sppiy the hinemstie equetiehs. New we are ready te d0 ists sf examples. ,. ...
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 Spring '08
 GUERRA
 Physics

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