Newton's Lesson 10

8/10/2019 Newton's Lesson 10

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NEWTONS LESSON 10

ELEVATOR PHYSICS

What are the forces at play on our bodies during the ride?

During the upward acceleration?

Normal force exceeds we!"#$ a%d #"e &od' feels "ea(' &eca)se #"e floor of

#"e ele(a#or s *)s"%! )s )* "arder #"a% )s)al+

During constant velocity between floors?

No %e# force o% o)r &odes a%d #"e rders feel rela#(el' %ormal+

During downward acceleration?

Normal force s less #"a% o)r we!"#$ a%d #"e &od' feels l!"# &eca)se #"e

floor s %o# *)s"%! )s )* as "ard as # ord%arl' does a%d #"ere s less force

o% #"e soles of o)r fee#+

W"a# 'o) feel$ we call # 'o)r apparent weight$ s %o# #"e *)ll of !ra(#'

dow% o% 'o)$ ra#"er what you feel as your weight is the floor pushing up on

you+

, I% o#"er words$ #"e a**are%# we!"# 'o) feel s ac#)all' #"e %ormal force of

#"e ele(a#or floor ac#%! o% 'o) -.a**are%#/ .N+

, T"e %ormal force c"a%!es d)e #o

#"e mo#o% of #"e ele(a#or floor+


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If 'o) are accelera#%! )* -.%e# 0 'o)r Apparent weight will be greater+

-Examples????: Accelera#%! as 'o) !o from res# a%d asce%d$

decelera#%! as 'o) come #o a s#o* a# #"e !ro)%d floor

If 'o) are accelera#%! dow% -.%e#2 0 'o)r apparent weight will be

smaller+

-Examples????: 3ecelera#%! as 'o) come #o a s#o* a# #o* of #"e

rde$ accelera#%! as 'o) !o from res# a%d desce%d dow%

W"e% 'o) are a# res# or mo(%! a# co%s#a%# s*eed -.%e# /0 'o)r apparent

weight will be your normal weight+

Exam*le4

If 'o) %ormall' we!" 506 N$ w"a# s 'o)r a**are%# we!"# f 'o) are % a%

ele(a#or #"a# s slow%! dow% a# #"e ra#e of 1+67 m8s9:

.rs#$ draw a free &od' da!ram a%d de#erm%e #"e drec#o% of accelera#o%4

Accelera#o% s dow%ward as #"e drec#o% of mo#o% s )* &)# #"e o&;ec# s

slow%! dow% a%d com%! #o a res#$ #"erefore #"ere s a% accelera#o%

dow%ward+

Seco%d$ de#erm%e #"e mass of #"e o&;ec# )s%! #"e .!4

.!/ m!

m / .!8! / 5068


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T"rd$ de#erm%e a% e@)a#o% #"a# re*rese%#s #"e forces ac#%! o% 'o)4

.%e#/ .! .N51+B-1+67 / 506 .N

.N/ 506 11=+5>69 / 7=5 N$ )*

Exam*le4

A lam* "a%!s (er#call' from a cord % a% ele(a#or w"c" s desce%d%! w#"

a% dow%ward accelera#o% of a/9+00m8s9+ T"e #e%so% % #"e cord s

.T/10+0N+ W"a# s #"e mass m of #"s lam*:


Accelera#o% s dow%ward+

Seco%d$ de#erm%e a% e@)a#o% #"a# re*rese%#s #"e forces ac#%! o% #"e lam*4

.%e#/ .! .TmB-9+00 / mB-


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Exam*le4

A 1900+0 ?! roc?e# *rod)ces D0000+0 N of #"r)s#+ W"a# s #"e s*eed of #"e

roc?e# >7+0 s af#er la)%c":


Accelera#o% s )*ward+

Seco%d$ de#erm%e a% e@)a#o% #"a# re*rese%#s #"e forces ac#%! o% #"e roc?e#

a%d f%d #"e accelera#o% of #"e roc?e#4

.%e#/ .#"r)s# .!1900-a / D0000 1900B-


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NEWTN!" #E""N $% &'EW()

1+ W"a# s #"e accelera#o% of a% ele(a#or a# res#:9+ W"a# s #"e %e# force w"e% #"e ele(a#or #ra(els a# a co%s#a%# (eloc#':

D+ W"e% do mos# ele(a#ors accelera#e d)r%! #"er mo#o%:

>+ W"e% s #"e %e# force o% #"e ele(a#or %o# 0+0 N:

Elevator at (est or 'oving at *onstant +elocity4

7+ W"e% a *erso% s#a%ds o% a &a#"room scale w"le o% #"e ele(a#or$ w"a# s "s we!"#w"e% #"e ele(a#or s a# res#:

6+ Fo(%! a# co%s#a%# s*eed:

5+ W"a# s #"e %e# force ac#%! o% #"e *erso%:=+ W"a# s #"e accelera#o% of #"e *erso%:

Elevator Accelerating ,pward4

+ W"e% wo)ld #"e *asse%!er feel we!"#less o% a% ele(a#or:

17+ W"' does #"e *asse%!er feel we!"less: -H%#4 w"a# s #"e (al)e of #"e %ormal force:

16+ W"a# "a**e%s #o #"e *asse%!er w"e% #"e ele(a#or accelera#es dow%ward a# a (al)e!rea#er #"a% +0m8s9

HINT4 Ha(%! #ro)&le co%(er#%! .N%#o ?!: W"e% was #"e las# #me 'o) saw a

&a#"room scale !(e a read%! % New#o%s: Yo) ca% c"a%!e #"s %#o a read%! %

?lo!rams &' remem&er%! #"a# #"e scale weGre )s%! "as %o dea w"a# s !o%! o%+++ #s#ll #"%?s #Gs s##%! % someo%eGs &a#"room w"ere !ra(#' s a %ce co%s#a%#


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90+ A ;e# accelera#es (er#call' )* a# =+7 m8s9+ W"a# force does #"e ex"a)s# !as exer# o%

#"e >>00 ?! ;e#:

91+ A 9+00 ?! *e%d)l)m "a%!s % a% ele(a#or+ Calc)la#e #"e #e%so% % #"e s#r%!s)**or#%! #"e *e%d)l)m f #"e ele(a#or mo(es4

a+ w#" Kero (eloc#'

&+ dow%ward a# a co%s#a%# (eloc#' of 9+7 m8sc+ )*ward a# a co%s#a%# (eloc#' of 9+7 m8s

d+ dow%ward a# a co%s#a%# accelera#o% of 9+00 m8s9

e+ )*ward a# a co%s#a%# accelera#o% of 9+00 m8s9

99+ A ma% meas)res #"e accelera#o% of a% ele(a#or &' )s%! a s*r%! &ala%ce+ He fas#e%s

#"e scale #o #"e roof$ a%d s)s*e%ds a mass from #+ T"e scale reads


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15+ .N1=+ .N1 ?!90+ =+1 x 10>N91+ a+ 1


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S%ce #"e ele(a#or s a# res#$ 'o)r accelera#o% s 0 m8s 9+ S%ce 'o)r accelera#o% s 0 m8s9$

Newton0s 1irst #awsa's #"e %e# force o% 'o) m)s# &e 0 New#o%s+

S%ce #"e %e# force o% 'o) s 0 New#o%s$ #"e )*ward forces a%d dow%ward forces o% 'o)

m)s# &ala%ce exac#l'+ T"erefore #"e scale m)s# *)s" o% 'o) w#" a force of -1a New#o%s$ a%d #"e scale m)s# read -1& New#o%s+

2uestion 3: .f you let go of the apple4 what does it do?

Answer:

T"e a**le wo)ld &e % free fall$ so #s accelera#o% rela#(e #o #"e ear#" s 10 m8s9

dow%ward+ S%ce 'o) are a# res# rela#(e #o #"e ear#"$ #"e a**leGs accelera#o% rela#(e #o

'o) wo)ld &e10 m8s9also$ so #"e a**le wo)ld a**ear #o fall ;)s# as # does a%'w"ere else

o% #"e ear#"+

-art 5: The Elevator Accelerates ,pward/

T"e ele(a#or$ -w#" 'o) %sde &e!%s

#o accelera#e )*ward from res# a# 9

m8s9+

2uestion 6: What will the scale

read now?

Answer:

T"ere are 9 forces ac#%! o% 'o)+

-Com*le#e #"e da!ram+ Yo)r we!"#

*)lls dow% w#" a force of 700

New#o%s+ T"e scale *)s"es )* w#" a

force of -Da -see &elow New#o%s+

S%ce 'o)r accelera#o% s 9 m8s9)*ward$ New#o%Gs Seco%d Law sa's #"a# #"ere m)s# &e a

%e# force *)s"%! 'o) )*ward$ a%d #"e %e# force "as a ma!%#)de .%e#/ ma+ So #"e %e#

force o% 'o)$


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S%ce #"e ele(a#or s mo(%! w#" co%s#a%# (eloc#'$ 'o)r accelera#o% s -7& m8s9+

S%ce 'o)r accelera#o% s -7c m8s9$ New#o%Gs .rs# Law sa's #"e %e# force o% 'o) s

-7d New#o%s+

S%ce #"e %e# force o% 'o) s -7e New#o%s$ #"e scale m)s# *)s" o% 'o) w#" a forceof -7f New#o%s$ a%d #"e scale m)s# read -7! New#o%s+

2uestion 9: .f you let go of the apple4 what does it do?

-art D: The Elevator "lows Down While ;oing ,p+ W"e% s #"e %e# force o% #"e ele(a#or %o# 0+0 N:

Elevator at (est or 'oving at *onstant +elocity4

7+ W"e% a *erso% s#a%ds o% a &a#"room scale w"le o% #"e ele(a#or$ w"a# s "s we!"#w"e% #"e ele(a#or s a# res#:


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6+ Fo(%! a# co%s#a%# s*eed:

5+ W"a# s #"e %e# force ac#%! o% #"e *erso%:

=+ W"a# s #"e accelera#o% of #"e *erso%:

Elevator Accelerating ,pward4

+ W"e% wo)ld #"e *asse%!er feel we!"#less o% a% ele(a#or:

17+ W"' does #"e *asse%!er feel we!"less: -H%#4 w"a# s #"e (al)e of #"e %ormal force:

16+ W"a# "a**e%s #o #"e *asse%!er w"e% #"e ele(a#or accelera#es dow%ward a# a (al)e

!rea#er #"a% +0m8s9

HINT4 Ha(%! #ro)&le co%(er#%! .N%#o ?!: W"e% was #"e las# #me 'o) saw a

&a#"room scale !(e a read%! % New#o%s: Yo) ca% c"a%!e #"s %#o a read%! %

?lo!rams &' remem&er%! #"a# #"e scale weGre )s%! "as %o dea w"a# s !o%! o%+++ #s#ll #"%?s #Gs s##%! % someo%eGs &a#"room w"ere !ra(#' s a %ce co%s#a%#


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m / .N8 !

/ ->00-=+7 / .#"r)s# >>00B-


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&+ co%s#a%# (eloc#' mea%s #"ere s %o accelera#o% a%d #"erefore %o .%e##"erefore #"e

#e%so% % #"e s#r%! wo)ld e@)al #"e we!"# of #"e *e%d)l)m / 1


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9D+ A fs" "a%!s from a s*r%! scale s)**or#ed from #"e roof of a% ele(a#or+ If #"e ele(a#or

"as a% )*ward accelera#o% of 1+9 m8s9 a%d #"e scale reads 900+0 N$ w"a# s #"e #r)e force

of !ra(#' o% #"e fs": -& %der w"a# crc)ms#a%ces wll #"e scale read 170 N a%d w"a#wo)ld &e #"e accelera#o% of #"e ele(a#or: -c W"a# wll #"e scale read f #"e ele(a#or

ca&le &rea?s: -1+= x 109N$ 1+7 m8s9$ :

A%swer4

a+ .rs#$ draw a free &od' da!ram a%d de#erm%e #"e drec#o% of .%e#o% #"e ele(a#or4

Seco%d$ de#erm%e a% e@)a#o% #"a# re*rese%#s #"e forces ac#%! o% #"e fs" a%d de#erm%e

#"e .!4

.%e#/ .T .!

m-1+9 / 900 m-+0me#er clff w#" a "orKo%#al

s*eed of 9=+0 m8s+ W"a# ds#a%ce from #"e &o##om of #"e clff does #"e &all la%d: Please

s"ow 'o)r wor? % a% or!a%Ked fas"o% -ls#%! ?%ow% a%d )%?%ow% (al)es -9D+5 m

A%swer4

dxf/ ::: d'/ 1>+0 m


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(x/ 9=+0 m8s

ax/ 0 m8s8s -#r)e for all *ro;ec#les

('/ 0+0 m8s -#s la)%c"ed "orKo%#all'

a'/ +0 / 0 0+7-7

Now #"e # (al)e ca% &e com&%ed w#" #"e (xa%d ax(al)e a%d )sed % a% "orKo%#al

e@)a#o%

dfx dx/ (x , #

dfx 0 / 9=+0-0+=>7

dfx/ 9D+66 / 9D+5 m


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ANSWER MEY .OR ELEVATOR WORMSHEET

A+ Ele(a#or A# Res#

1+ W"a# does #"e scale sa':

a+ scale *)s"es w#" a force of 8%%New#o%s -#o &ala%ce #"e Ear#"Gs*)ll

&+ scale sa's 8%%New#o%s -e@)al #o #"e scaleGs *)s"

9+ W"a# does #"e a**le do:

Q+ Ele(a#or Accelera#es *

D+ W"a# does #"e scale read: To com*le#e #"e force da!ram 'o) %eed #o a%

)*ward force o% 'o) d)e #o #"e scale+ T"s force #)r%s o)# #o &e 600

New#o%s see &elow+

a+ #"e scale *)s"es w#" a force of 9%%New#o%s$ s%ce w"e% #"escaleGs force s com&%ed w#" #"e Ear#"Gs force -we!"# / 700

New#o%s #"ere "as #o &e a 100 New#o% force -)*ward lef# o(er

#"e %e# force+


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&+ 9%%New#o%s -same as *ar# a

c+ 9%%New#o%s -same as #"e force #"e scale exer#s

>+ W"a# does #"e a**le do:

T"e a**le wo)ld &e % free fall$ so #s accelera#o% rela#(e #o #"e ear#" s

10 m8s9dow%ward+ S%ce 'o) are accelera#%! a# 9 m8s9)*ward rela#(e #o

#"e ear#"$ #"e a**leGs accelera#o% rela#(e #o 'o) wo)ld &e 10 m8s 9 9

m8s9/ 19 m8s9$ so #"e a**le wo)ld a**ear #o fallfaster%sde #"e ele(a#or

#"a% # does % %ormal free fall o% #"e ear#"+

To #"e occ)*a%#s of #"e )*wardl' accelera#%! ele(a#or$ #

appears that gravity is stronger$ s%ce #"e'seem to weigh more-w"': a%d o&;ec#s fall fas#er #"a% %ormal+

C+ Ele(a#or a# Co%s#a%# Veloc#'

6+ W"a# does #"e scale read: To com*le#e #"e force da!ram$ 'o) %eed #o add

a% )*ward force o% 'o) d)e #o #"e scale+ T"s force #)r%s o)# #o &e 700New#o%s see &elow+

a+ T"e scaleGs force o% 'o) s 8%%New#o%s+ -see &elow

&+ Yo)r accelera#o% s %m8s9-s%ce 'o)r (eloc#' s co%s#a%#

c+ %m8s9-same as *ar# &d+ T"e %e# force m)s# &e %New#o%s -f #"e accelera#o% s 0 m8s9+

e+ %New#o%s -same as *ar# d

f+ T"e scaleGs force m)s# &e 8%%New#o%s s%ce # m)s# exac#l'

&ala%ce 'o)r we!"# -700 New#o%s so #"a# #"e %e# force s 0New#o%s+

!+ T"e scale reads 8%%N -same as #"e scaleGs force+

5+ W"a# does #"e a**le do f 'o) le# !o: T"e a**le wo)ld &e % free fall$ so #saccelera#o% rela#(e #o #"e Ear#" wo)ld &e


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f+ $%%N -same as *ar# e

!+ $%%N -same as *ar# e

"+ T"e scaleGs force s 7%%New#o%s$ s%ce # m)s# com&%e w#" 'o)rwe!"# -700 New#o%s #o lea(e a %e# dow%ward force of 100

New#o%s+

+ T"e scale reads 7%%New#o%s -same as scaleGs force


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Newton's Lesson 10

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