understanding gravity - physics form 4
TRANSCRIPT
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-Acceleration Due to
Gravity.-Gravitational Field.
-Gravitational Field
UNDERSTANDING
GRAVIT
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!et"# te#t your $e$ory %
I& you thro' an o()ect* 'hat 'illha++en,
The o()ect 'ill &alling do'nWhat i# Ne'ton"# Second !a',Ne'ton #tated the relation#hi+
(et'een &orce* $a## andacceleration.
F$a
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The a++le #tory
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GRAVITIntroduce# (y Sir I#aac Ne'ton.()ect# &all (ecau#e they are
+ulled to'ard# the Earth (y the
&orce o& gravity.
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keeps things on the
earth.
pull of gravitational forc
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brings things down to earthwhen they are thrown upwards.
e pull of gravitational for
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holds the moon in itsorbit round the Earth.
e pull of gravitational for
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keeps things on the earth.brings things down to earthwhen they are thrown
upwards.holds the moon in its orbitround the Earth.
force, F/
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A00E!ERATIN DUE T GRAVIT
Figure #ho'# a #tro(o#co+ic+hotogra+h o& a (all &allingunder gravity
The di#tance (et'een t'o#ucce##ive i$age#increa#e#* #ho'ing that the
(all are &alling 'ithincreasing velocity , i.e.*&alling 'ith an acceleration
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The acceleration o& o()ect# &alling &reely i# 1no'na# the acceleration due to gravity, g = 10 ms
!2value &ro$ e3+eri$ent4.
There&ore* F $g
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A00E!ERATIN DUE TGRAVIT
n the late 56thcentury* GalileoGalilei dro+# t'o o()ect o&
di7erent $a## &ro$ the !eaningTo'er o& 8i#a and &ound out thatthe o()ect &all 'ith the #a$e
acceleration 2hit the ground atthe #a$e ti$e4 .
Thi# e3+eri$ent to di#+rove
Ari#totle9# theory o& gravity* 'hich
http://en.wikipedia.org/wiki/Aristotlehttp://en.wikipedia.org/wiki/Aristotle -
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The !eaning To'er o& 8i#a 2Italy4
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()ect# 'ith di7erent $a##'ould &all 'ith sameacceleration a##u$ing thatthere i# no air re#i#tance
In other 'ord#* gravitationalacceleration i# independentof mass.
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:!E inventedvacuu$ +u$+ tore$ove air.
In vacuu$* (oth
o()ect# reach the(otto$ o& thecylinder at the
#a$e ti$e.In at$o#+here* a
+iece o& ti##ue
+a+er doe# not
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E3+eri$ent in the $oon to te#t Galelio"# #tate$ent
:UT; WE 0ANT D thi# te#t in the earth
(ecau#e there are air re#i#tance 'hicho o#e# the ullin &orce o& ravit .
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A freefalling o()ect i# ano()ect &alling under the &orce o&gravity only.
A &ree-&alling o()ect doe# notencounter other &orce# li1e airresistance or friction that
'ould o++o#e it# $otion
FREE FA!!
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!et"# #ee the e7ect o& air re#i#tance'ith $a1ing our o'n #$all +arachute
"hysics behind the parachute #
Every o()ect 'ill &all do'n 'ith
acceleration o&
.The +arachute e3+erience# the air
re#i#tance and o++o#e# the +ulling &orce o&gravity.
Air re#i#tance e3+erience# (y an o()ectde+end# on it# #ha+e.
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$ravitational %eld is a regionaround the Earth in which an
ob&ect e'periences a force
towards the centre of the earth.
F()*E (F$)+-TF()*E (F
$)+-T
F()*E (F
$)+-T
F()*E (F$)+-T
GRAVITATINA! FIE!D
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The gravitational %eldstrength i# de?ned a# the
force acting on unit mass inthe ?eld.
The gravitational ?eld #trength
at the surfaceo& the Earthi#/. kg1.
g = F2m /
F Gravitational &orce
GRAVITATINA! FIE!DSTRENGT@
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WEIG@T* WThe 'eight o& an o()ect i#de?ned a# the gravitational&orce acting on the o()ect.
F $a
W $g3nit is the same as force, E'ample # ! kg = !0
g is thegravitationalaccelerati
on
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EAB8!E 5A $ar(le i# dro++ed &ro$the to+ o& a (uilding and
ta1e# > # to reach the#ur&ace o& the Earth. Whati# the height o& the(uilding ,
2>C $4
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A roc1 ha# a $a## o&>C.C 1g and 'eight o&
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SUBBAR