force 2.7.2.8

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2.8 Gravity

8/17/2019 force 2.7.2.8


Form 4© COPYRIGHT BY SUPER EDUCATION GROUP (JO

2.8 Grav!"

PREPARED BY JJ #R$EON Pa%& '© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)

8/17/2019 force 2.7.2.8


Safety features in vehicles

Cra r&!a*! +oor ,--ar

A*!-o/0 1ra0& "!&m (ABS)

Tra/!o* /o*!ro- 1m,&r

3*+/r&&*

Ar 1a%

H&a+ r&!

Crm,-& o*&

2.8 Grav!"

2.7 BEING AWARE OF TE NEE! FOR SAFET" FEAT#RES IN $EI%&ES

I'()rtance )f safety features in vehicles

Safety features I'()rtance

Pa++&+ +a1oar+Increases the time interval of collision so the impulsive force

produced during an impact is thereby reduced

R11&r 1m,&r Absorb impact in minor accidents, thus prevents damage to the

car.

Sa!!&r,roo5 6*+/r&&* Prevents the windscreen from shattering

Ar 1a% Acts as a cushion for the head and body in an accident and thus

prevents injuries to the driver and passengers.

Sa5&!" &a! 1&-!

Prevents the passengers from being thrown out of the car. Slows

down the forward movement of the passengers when the car

stops abruptly /suddenly.

S+& 1ar * +oor

Prevents the collapse of the front and back of the car into the

passenger compartment. Also gives good protection from a side

on collision.

Fro*! /rm,-& o*&

R&ar /rm,-& o*&

!rumple upon impact and lengthen the period of the time for the

car to stop. Impulsive force is reduced.

Protect passengers from rear impact

A*! 7 -o/0*% 1ra0*%

"!&m (ABS)

"nable the driver to #uickly stop the car without causing the

brake to lock.

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Reinforced passenger compartment

8/17/2019 force 2.7.2.8


2.8 Grav!"

2.8 #N!ERSTAN!ING GRA$IT"

Acceleration due to gravity.

1. An object will fall to the surface of the earth because………………………………...2. The force of gravity also known ………………………………………………………...

The earth’s gravitational force tend to pull everything towards its centre.

3. hen an object falls under the force of gravity only! ………………………………...

………………………………………………………………………………………………

". The acceleration of objects falling freely ………………………………………………

#. The $agnitude of the acceleration due to gravity depends ………………………...

………………………………………………………………………………………………Gravitational field

1. The region around the earth is ………………………………………………………….

2. The object in gravitational field …………………………………………………………

3. The gravitational field strength is defined ……………………………………………..

". The gravitational field strength! g can be calculate as%

#. At the surface of the earth! …………….

………………………………………………………………………………..

&. This $eans ……………………………………………………………………………………………..

'

PREPARED BY JJ #R$EON Pa%& © COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)

It pulled by the force of gravity.

as earth$s gravitational force.

the object is said to be free

falling

is known as acceleration due to gravity.

on the strength of the gravitational

%eld

. the gravitational %eld of the earth.

is on the force of gravity.

as the gravitational force acting on a & kg

mass.

. g ' ( . where, ( ) gravitational force

m m ) mass of an object

g ' *.+ kg& that an object of mass & kg will e-perience a

gravitational force of *.+ .

8/17/2019 force 2.7.2.8


2.8 Grav!"

Example 1. (an you esti$ate the gravitational force act to your body)

$ass * &+ kg! g * ,.- kg/1! 0 * )

Solution ) ( ' mg ' 01 *.+1

' 2++.0

Example 2, A satellite of $ass &++ kg in orbit eperiences a gravitational force of "-++ . (alculate the

gravitational field strength.

3iven ) m ' 00 kg. ( ' 4+00 , g ' 5

g ' (

' 4+00 .

' + kg&

m 00

E*a'(le +,

A !o*& r&-&a&+ 5rom r&! a*+ 5a-- *!o a 6&--. A5!&r '.2 9 ! ! !& 1o!!om o5 !&

6&--.

(a) 3a! !& v&-o/!" o5 !& !o*& 6&* ! ! !& 1o!!om:

(1) Ca-/-a!& !& +&,! o5 !& 6&--.

Wei-ht

'. T& 6&%! o5 a* o1;&/! +&<*&+ ====================..

2. For a* o1;&/! o5 ma m9 !& 6&%! /a* 1& /a-/-a!& a >


3iven ) u ' 0 ms&, t ' &.6 s, a ' g ' *.+ ms6

a1 v ' 5 v ' u 7 at

' 0 7 *.+1&.61

' &&.8 ms&

b1 9epth ' s ' 5 s ' ut 7 : at 6

' 01&.61 7 : *.+1&.616

' 8.02& mas the gravitational force acting on the object.

weight, ; ' mg

where, g ' acceleration due to gravity.

8/17/2019 force 2.7.2.8


2.8 Grav!"

Differences between Weigt and !ass

Weigt !ass

epends on the gravitational field strength ndependent fro$ the gravitational field strength

4ector 5uantity 6calar 7uantity

8nit ewton 9: 8nit; <ilogra$ 9kg:

Fr&& 5a-- S!+"

At vacuu' state At N)r'al State

T&r& *o Ar r&!a*/& Bo! !& /o* a*+ !& 5&a!&r 6-- 5a--

1&/a& o5 %rav!a!o*a- 5or/&. T& /o* a*+ !& 5&a!&r 6-- 5a--

5r&&-"

Ar r&!a*/& a?&/!&+ 1" !&

r5a/& ar&a o5 a 5a--&* o1;&/!.O*-" %rav!a!o*a- 5or/& a/!*%

o* !& o1;&/!.

T& 5&a!&r !a! a a -ar%&r r5a/&

ar&a 6-- av& mor& r&!a*/&Bo! 6-- r&a/ !& 1o!!om a! !&

am& !m&

T& /o* 6-- r&a/ !& 1o!!om <r!.

E*a'(le T& ma o5 a

&-/o,!&r @ 0%. 3a!

!& 6&%! o5 !& &-/o,!&r

6&* ! -a*+ o* !& ,&a0 o5 a

mo*!a* 6&r& !& %rav!a!o*a- <&-+ .8 N 0%':

; ' mg

' 00 - *.8+

' 2+ +

Example 2" A coconut tree 2.+s to fall to the ground. hat is

a: its speed just before is strike the ground

b: the height of the coconut tree.


8/17/2019 force 2.7.2.8


2.8 Grav!"

Example # " A rock has a $ass of 2+.+kgand weight of ,+.+ on the surface of the planet.

a: hat is the gravitational field strength on the surface of the planet)

b: hat are the $ass and the weight of the rock on the surface of the earth where its gravitational field strength

is ,.-kg/1 .

E*ercise

)l/ t0) st)nes 0ith /i1erent sies at the sa'e hei-ht an/ then /r)( 3)th

st)ne si'ultane)usly fr)' the sa'e hei-ht.

(a) 3a! a,,&* !o 1o! !o*&:

(1) D&/r1& o6 !& v&-o/!" /a*%& +o&.

(/) Com,ar& !& !m& !a0&* 5or !& !o*& !o r&a/ !& oor.

(+) Ar& !& a//&-&ra!o* o5 !& !o*& *&*/&+ 1" !&r ma&:

PREPARED BY JJ #R$EON Pa%& @© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)

8/17/2019 force 2.7.2.8


2.8 Grav!"

Activity + Which )ne reaches the -r)un/ 4rst5

)l/ a -)lf 3all an/ a (iece )f (a(er

at the sa'e hei-ht an/ /r)( the'

si'ultane)usly.

Re(eat 0ith a -)lf 3all an/ a (iece

)f (a(er 0hich is cru'(le/5

(a) 3/ o1;&/! r&a/& !& oor <r!: (/) 3/ o1;&/! r&a/& !& oor <r!:

(1) E,-a* 6". (+) E,-a* 6"


8/17/2019 force 2.7.2.8


2.8 Grav!"


8/17/2019 force 2.7.2.8


2.8 Grav!"


8/17/2019 force 2.7.2.8


2.8 Grav!"

&ift

'. 3&* a ma* !a*+*% *+& a* &-&va!or9 !&r& ar& !6o 5or/& a/!*% o* m.

a. H 6&%!9 (3) 6/ a/!*% +o6*6ar+.

1. Norma- r&a/!o* (R)9 a/!*% * !& o,,o!& +r&/!o* o5 6&%!.

2. T& r&a+*% o5 !& 1a-a*/& &a- !o !& *orma- r&a/!o* (R).

. F%r& 1&-o6 o6 !& 5orm-a !o /a-/-a!& !& r&a+*% o5 !& 1a-a*/& a! +?&r&*!

!a!o*.


8/17/2019 force 2.7.2.8


2.8 Grav!"

6ulley

PREPARED BY JJ #R$EON Pa%& ''© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)

8/17/2019 force 2.7.2.8


2.8 Grav!"

PREPARED BY JJ #R$EON Pa%& '2© COPYRIGHT BY SUPER EDUCATION GROUP (JOHOR JAYA)

8/17/2019 force 2.7.2.8


2.8 Grav!"


8/17/2019 force 2.7.2.8


2.8 Grav!"

2.8 Grav!a!o*a- For/&

&!o* ' (SP# 2')

Figure 17 is a stroboscopic photograph shows two steel balls in a state of free- fall. Bothballs are dropped

simultaneously from the same height..

$a% =bserve the photograph and state two si$ilarities between the position

of the balls.

>2 $?

$c% a$e one physical 5uantity which

causes the balls to fail.

>1 $?

$d% @ased on the positions of the free/ falling balls! there is a physical

5uantity that is constant.

$i% a$e the 5uantity.

>1 $?

$ii% hat is the value of the 5uantity and its unit)

>1 $?

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8/17/2019 force 2.7.2.8


2.8 Grav!"


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force 2.7.2.8