3. forces f2013 ave

18
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  Forces always act in pairs, acting on two different objects "#$%&'

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Page 1: 3. Forces F2013 Ave

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!

"#$%&'

(#)%&*+',"#$%&(-+&.#$/ #1 1#$%&'"$&& 2#3/ 34-.$-56784942$485

(:-*+&$, ;

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C:-+ 4' 1#$%&D

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;

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E I 1#$%& 4' - *8': #$ - *899 &G&$+&3 #) -)

#2J&%+K $&'89+4). 1$#5 +:& 4)+&$-%+4#) 2&+F&&)+F# #2J&%+'K '8%: -' +:& *&$'#) -)3 +:& %-$+H

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=

E L4)%& +:& 4)+&$-%+4#) 4' 2&+F&&) +F# #2J&%+'K+:&$& -$& +F# 1#$%&'K #)& #) &-%: #2J&%+

E I 589& -**94&' - 1#$%& #) - %-$+K -)3 +:& %-$+-**94&' - 1#$%& #) +:& 589&K '4589+-)&#8'9/M NF4+:+:& '-5& 5-.)4+83& 28+ 4) #**#'4+& 34$&%+4#) OH – Forces always act in pairs, acting on two different objects

"#$%&'

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P

Broad Categories of Forces:E Contact forces , $&784$& *:/'4%-9 %#)+-%+

2&+F&&) +F# 4)+&$-%+4). #2J&%+'H

E Contact free forces , $&784$&no %#)+-%+2&+F&&) +F# 4)+&$-%+4). #2J&%+' -)3 -%+' #Q&$- 34'+-)%&

E R:&'& 1#$%&' 5-/ 2& 9#). $-).& 1#$%&'

E (#)+-%+ 1$&& 1#$%&' -$& -9'# %-99&3field forces

"#$%&

@

E <$#*&$+4&' #1 1#$%&', S "#$%& 4' - *8': #$ - *899 +:-+ #)& #2J&%+ &G&$+' #)

-)#+:&$H S "#$%& &4+:&$ 4' - %#)+-%+ 1#$%& #$ 4' - %#)+-%+ 1$&&

1#$%&H S "#$%& 4' - Q&%+#$K :-Q4). 2#+: 5-.)4+83& -)3

34$&%+4#)H S "#$%&' -$& *-4$&3H RF# 4)+&$-%+4). #2J&%+' &G&$+ -

1#$%& #) &-%: #+:&$K -+ +:& '-5& +45&H S "#$%&' -$& -334+4Q&H R:& &11&%+ #1 +F#

'4589+-)&#8' 1#$%& #) - '-5& #2J&%+ 4' +:& '-5&-' +:& )&+ 1#$%& #1 +:& +F# 1#$%&'H

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T

C:-+ 3#&' - 1#$%& 3#D

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E C:&) /#8 U4%U - 2-99K /#8$ 1##+ &G&$+' - 1#$%&#) +:& 2-99 F:49& +:& +F# -$& 4) %#)+-%+! K%:-).4). +:& Q&9#%4+/B N+:& '*&&3 -)3V#$ +:&34$&%+4#)O #1 +:& 2-99H

E ! ,?? "#$%& 4' -) 4)+&$-%+4#) 2&+F&&) +F##2J&%+'H

E B,?? "#$%& N&G+&$)-9O %:-).&' +:& Q&9#%4+/Kcauses acceleration K #1 +:& #2J&%+H

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211 s

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E ^_ Y_R L`Z< RaZL LR6< _\ b_XCZcc [6 c_LR "_\ Ra6 \6LR _"Ra6 R6\de

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y x A A A

cos A A x

sin A A y

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A tan y x A A A ,

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iy y F R

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ix x F R

21 F F R

I '45*9& F-/ +# 14)3 +:& $&'89+-)+ #1 +F#Q&%+#$' 4' 14)34). +:& %#5*#)&)+' #1 4+H!H "4)3 +:& G -)3 / %#5*#)&)+' #1 &-%:Q&%+#$HBH G?%#5*#)&)+ #1 $&'89+-)+ 4' +:&'855-+4#) N-9.&2$-4%-99/O #1 G?%#5*#)&)+' #1 Q&%+#$'H;H /?%#5*#)&)+ #1 $&'89+-)+ 4' +:&'855-+4#) N-9.&2$-4%-99/O #1 /?%#5*#)&)+' #1 Q&%+#$'H

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B;

<$-%+4%&, R#+-9 "#$%& #) -) #2J&%+E Z) +:& 14.8$& 2&9#FK 1#$ F:-+ Q-98& #1 F499

( f I g [ :-Q&, N at home O

-H I 54)4585 Q-98&2H I 5-G4585 Q-98&%H "4)3 ( 1#$ f AW#H

IfP

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BP

<$-%+4%&, R#+-9 "#$%& #) -) #2J&%+E "#$ +:& Q&%+#$' 4) 14.8$&K "4)3 +:& 5-.)4+83&

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C B A D

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at home

BT

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E "8)3-5&)+-9 "#$%&' S %#)+-%+?1$&& 1#$%&'

S %-))#+ 2& &G*9-4)&3 -' -)/ %#5*#)&)+ #1#+:&$ 1#$%&'

E (#)Q&)4&)%& "#$%&' N)#)?18)3-5&)+-9O S (-) 2& &G*9-4)&3 4) +&$5' #1 18)3-5&)+-9

1#$%&'

B>

"#$%&"8)3-5&)+-9 +/*&' #1 1#$%&', _)9/ 1#8$ +/*&',

E i$-Q4+/ N9#). $-).& O S the force between masses S holds planets and stars together, makes things fall, etc

E 69&%+$#5-.)&+4% N9#). $-).& O S the force between charges, magnets, S responsible for all familiar “everyday” forces (except

gravity)

E L+$#). N':#$+ $-).& O S holds atomic nuclei together

E C&-U N':#$+ $-).& O S Beta decay (radioactivity)

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BA

"#$%&

E +:& 1#$%& +:-+ -++$-%+' #)&5-'' +# -)#+:&$

E I)/ +F# #2J&%+' &G&$+.$-Q4+-+4#)-9 1#$%& #) &-%:#+:&$H

g F

g F

i$-Q4+-+4#)-9 1#$%& Ni$-Q4+/O,

;W

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E \&'*#)'429& 1#$ U&&*4). +:& 6-$+: -)3 *9-)&+'#$24+4). +:& L8)H

;B

"#$%&E Y&F+#)j' 9-F #1 8)4Q&$'-9 .$-Q4+-+4#),

E C:&$&,

– m1 -)3 mB -$& +:& #2J&%+' 5-''&'K – r 4' +:& 34'+-)%& 2&+F&&) +:&5K – G 4' +:& 8)4Q&$'-9 .$-Q4+-+4#)-9 %#)'+-)+H

2

21

r

mmG F 22111067.6 kg m N G

;;

"#$%&Y&F+#)j' 9-F #1 8)4Q&$'-9 .$-Q4+-+4#),

• An attractive gravitational force betweentwo objects is proportional to the product oftheir masses and inversely proportional tothe square of the distance between them.

2

21

r

mmG F

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;=

"#$%&6G-5*9&,E RF# =W U. #2J&%+' -$& *9-%&3 -+ +:& 34'+-)%& #1

=W %5 1$#5 &-%: #+:&$ %&)+&$H C:-+ 4' +:& 1#$%&#1 .$-Q4+/ #1 &-%: -%+4). #) +:& #+:&$D

2

21

r

mmG F

22111067.6 kg m N G

;@

C&4.:+E C:-+ F& %#55#)9/ %-99 F&4.:+ 4' $&-99/

+:& 1#$%& #1 .$-Q4+/ -%+4). #) - 2#3/

E Y&-$ +:& 6-$+:k' '8$1-%&,

E where g is the acceleration of an object dueto gravity. On the Earth, it is approximately

constant everywhere on the planet.

mg R M

Gm R M m

G F w E

E

E

E g

)(22

mg w

;T

"#$%&6G-5*9&,E (-9%89-+& +:& .$-Q4+-+4#)-9 -%%&9&$-+4#)K g d K -+

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2

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mmG F 22111067.6 kg m N G

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g mw

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=!

"#$%&E i$-Q4+-+4#)-9 I%%&9&$-+4#)

E On the Earth surface, it 4' -**$#G45-+&9/%#)'+-)+ &Q&$/F:&$&H

E I' /#8 $4'& -2#Q& +:& 6-$+:k' '8$1-%& +:&.$-Q4+-+4#)-9 14&93 F&-U&)'K '# g 3&%$&-'&'H

28.9

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g

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2

21

r

mmG F 22111067.6 kg m N G

=>

"#$%&

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611&%+ #1 .$-Q4+-+4#)-9 1#$%&,

<811/?1-%& -)3 24$3?9&. 9##U

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N&9&%+$4% l 5-.)&+4% 1#$%&O #) &-%: #+:&$H

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P!

"#$%&E (#89#52k' c-F

E C:&$&, – q1 -)3 qB -$& +:& 5-.)4+83&' #1 +:& %:-$.&' N4)

%#89#52 m(nOK – r 4' +:& 34'+-)%& 2&+F&&) +:&5K

– k 4' +:& (#89#52 %#)'+-)+H

2

21

r

qqk F 2291099.8 C m N k

PB

"#$%&(#89#52k' c-F

• An electric force between two charges is proportional to the product of the magnitudeof their chrges and inversely proportional tothe square of the distance between them.

2

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qqk F

P;

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5-'' #1 5 f !H@T G !W ? BT U.K 4) - )8%9&8' -$&'&*-$-+&3 -**$#G45-+&9/ 2/ BH= h !W ?!P 5H(#5*-$& +:& &9&%+$4% 1#$%& -)3 .$-Q4+-+4#)-9 1#$%&2&+F&&) +:&5H

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2291099.8 C m N k

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"#$%&

Convenience Forces

E I99 )#)?18)3-5&)+-9 N%#)Q&)4&)%&O 1#$%&' -$&contact forces H

E I+ +:& 54%$#'%#*4% 9&Q&9K +:& %#)+-%+ 1#$%&'-$& &9&%+$#5-.)&+4% 1#$%& 4) )-+8$&H

• They are the result of the interaction between thecharged particles that are contained in atoms and

molecules, which make molecular bonds betweenthem.

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"#$%&Convenience ForcesE 6Q&$/ 1#$%& /#8 -$& 1-5494-$ F4+:K #+:&$ +:-)

.$-Q4+/K 4' - 5-)41&'+-+4#) #1 +:& &9&%+$#5-.)&+4%1#$%& 2&+F&&) -+#5',

S Surface ForcesENormal forceEForce of Friction

S Tension S Spring force S Drag S Viscous force

@!

"#$%&L8$1-%& "#$%&,

E R:& '8$1-%& 1#$%& :-'+F# m%#5*#)&)+'n,

n

A F

g F

f

E Normal force , 4' *&$*&)34%89-$ +# +:&'8$1-%&' 4) %#)+-%+

E Force of friction , 4' *-$-99&9 +# +:& '8$1-%& #1

%#)+-%+

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+# +:& %#)+-%+ '8$1-%& 2&+F&&) +F# #2J&%+'@;

I 29#%U #) - +-29&,

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E R:& )#$5-9 1#$%& F499 2& -'9-$.& -' )&%&''-$/ +# :#93 +:&29#%U N8)+49 +:& +-29& 2$&-U'O

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"#$%&E "$4%+4#),+:& 1#$%& +:-+ $&'4'+' +:& 5#+4#)

#1 -) #2J&%+ -%$#'' -)#+:&$

S I%+' *-$-99&9 +# +:& %#)+-%+ '8$1-%&K 4)34$&%+4#) #**#'&' 5#+4#)

L+-+4% 1$4%+4#)E "$4%+4#),

`4)&+4% 1$4%+4#)

fric F v

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L+-+4% "$4%+4#),E _*&$-+&' F:&) R:&$& 4' )# $&9-+4Q& 5#+4#)

2&+F&&) +F# %#)+-%+4). '8$1-%&

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"#$%& #1 "$4%+4#)

W"

sf A F

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E d-.)4+83& #1 L+-+4% "$4%+4#),

E Where: s is coefficient of static friction,N is normal force

E equal to Applied force :

"#$%& #1 "$4%+4#)

N f s Max s

,

AFf

g m

N N f s s

A s F f TP

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5#Q4). *-'+ #)& -)#+:&$

E Z+ *#4)+' 4) +:& 34$&%+4#) +:-+ #**#'&' +:&5#+4#)H

"#$%& #1 "$4%+4#)

k f

v

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E d-.)4+83& #1 `4)&+4% "$4%+4#) ,

E Where: k is coefficient of kinetic friction,N is normal force

E It points in the direction that reduces therelative motion between the two surfaces

E R:4' 1$4%+4#) 4' F:&) +:& +F# '8$1-%&' -$&-9$&-3/ 5#Q4). $&9-+4Q& +# &-%: #+:&$

"#$%& #1 "$4%+4#)

N f k k AF

f

g m

N

TT

E "#$%& #1 L+-+4% "$4%+4#),E has a maximum value.E The maximum value is proportional to the

normal force the surfaces exert on eachother.

E Always is equal to applied force

E "#$%& #1 ̀ 4)&+4% "$4%+4#) ,E is approximately independent of velocityE Is smaller than the maximum static friction

force.E is also proportional to the normal force.

"#$%& #1 "$4%+4#)K <$#*&$+4&'

T>

"#$%& #1 "$4%+4#)

TA

E R&)'4#) , +:& m*8994).n 1#$%&K #)& #2J&%+ *899'#) -)#+:&$ S $&'89+' 1$#5 +:& '+$&+%:4). #1 5#9&%89-$ 2#)3'

"#$%&

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>;

L*$4). "#$%&E a##U&k' c-F,

"#$%&

x

F:&$&• x 4' +:& %:-).& 4) 9&).+: #1 '*$4). 1$#5 4+'

8)'+$&+%:&3 N#$ 8)%#5*$&''&3O 9&).+:K• k 4' +:& '*$4). %#)'+-)+

xk F

>=

a##Uk' c-FE Z1 /#8 '+$&+%: - '*$4).K :#F :-$3 4+ *899' /#8 2-%UD

E R:& 1#$%& &G&$+&3 2/ +:& '*$4). 4' F s = - k x S x 4' +:& *#'4+4#) #1 +:& 29#%U F4+: $&'*&%+ +# +:& &784942$485

*#'4+4#) N x f WOH

S k 4' +:& '*$4). %#)'+-)+ #$ 1#$%& %#)'+-)+ -)3 5&-'8$&'+:& '+411)&'' #1 +:& '*$4).H

E Applied force on the spring is: F App = k x

>T

"#$%&Drag Force

2

21

Av D R

R: drag forceD: drag coefficient : density of medium A: cross-sectional area

of the objectv: relative velocity withrespect to the medium

I 1#$%& +:-+ #**#'& +:& 5#+4#) +:$#8.: 947843' -)3 .-''&'

>>

"#$%&Viscous Force

rv F vis 6

F vis : Viscous force : viscosity of liquid

r: radius of sphericalobject

v: relative velocity withrespect to the medium

a#F $&'4'+4Q& +:& 19843 4' +# 19#F

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>A

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