111 The mag nitu de of centripe tal force
Ill I '
IS . / · WI 1ere F = Cen tripe tal
r
For ce
v = Velocity of bod y
r = radius of circle.
m= mass
IX - ST D PHYSICS SSIGNMENT 7.What is Centripetal acc eler atio n?
When a bod y moves in a circular path then
9.GRAVITATION acceleration generated due to change in
its
velocity is kno wn as centripetal accelera
tion.
(Page - 01) The direction of centripetal acceleration
is
1.What is Gravity ? towards the centre of circle.
The force with which the earth pulls the
objects 8. What is the source of centripetal forc
towards it, is called the gravity or gravitatio e
nal that a plan et requires to revolve arou
force of eart h . nd the
Sun? On wha t factors doe s that force
depend?
2.Give few examples whe re gravitati
onal
force of the earth is responsible: Gravitational force is the sou rce of centripe
tal
I.Atmosphere above the earth. force required to revolve arou nd the sun
. This
II. Rain falling to the earth . force depends on the dist anc e between
the
Ill.Flow of wat er in rivers . planet and sun along with thei r masses.
If this
force becomes zero as a result of the abs
ence
3.What is Gra vita tion ? of centripetal force, the plan et would shif
t to
Gravitation is the forc e of attraction betw move tangentially outwards to the circ ular
een route
any two obje cts in the univ erse .
9.The earth is acted upon by gravitati
4.What is the main diff eren ce between on of
Sun , even though it doe s not fall into
gravitation and gravity ? the
Sun. Why?
Gravitation is the forc e of attraction betw Sur prov ides enough centripetal forc e to
een keep
any two obje cts in the univ erse . the earth in its orbit and the earth provides
centrifugal forc e due to its motion . The se
two
Gravity is the force of attraction between forces bala nce each other which prevents
any the
object and the earth. earth from falling into the sun .
5.What is Centripetal For ce? Write its 10.What is the weight of an object at the
centre of the earth of radius R?
expression.
Centripetal forc e is a forc e which causes At the centre of the earth acceleration due
to
acceleration of a body, mov ing in a circu gravity is zero . Since weight is the product
lar of
path and acti ng towards the centre of the mass and gravity. Weight of an object at
the
centre of the earth will be zero .
circular path .
6. Explain Cen trip etal forc e and write 11.What is Gravitational Constant? Wha
its t is
expression. its value?
i. Whe nev er a bod y mov es in a circular The gravitational constant G is numerica
lly
path , velocity and the direction equal to the force of grav itation which exis
ts
cha nge s at eve ry point. between two bod ies of unit masses kep t
at a
ii. The force that cau ses this unit dista nce from each other The value
of
acceleration and keeps the bod y universa l grav1tat1onal constant G 1s
mov ing along the ci rcular path acting G = 6 67 x 10 ·11 Nm 2 I Kg 2
tow ards the ce ntre .
J
, - -- -· --- -- -- - - ( ,'111 I Ill
(Pago - 02)
ti
12.W hy is Newt on 's law of gra vilali on co llod
the unive rsal law ?
G 1s constant of proportiona lity. It is called
Newton's law of gravit ation 1s called tile universal gravitation constant.
u111versal law because it is applicable to all
2. Write the formula to find the magnitude of
bodie s, wheth er the bodies are big or small, the gravitational force between the earth
wheth er they are celestial of terrestrial. and an object on the surface of the earth.
13. Suppose gravity of earth suddenly (i .M e X m ,,
beco mes zero, then in which direction will F gravitation = - - -2
r
the moon begin to move if no other celestial
body affects it? Where G is gravitational constant
If there is no gravitational pull from the earth,
Me = The mass of the earth
the moon starts to move in a straight line
tange nt to its circular path.
M0 = The mass of the object
r = the distance between the centre of
14.Ex plain briefly how Newton discovered
the Law of Gravitation . of the object and the centre of the earth .
Newt on observed while sitting under an apple
tree that an apple fell down. He asked himself ----------------------------- -·-- ---- ---- ---- -
that if the earth can attract an apple and can it NCER T BOOK QUES TIONS PAGE : 104
also attract the moon ? He then, argued that at
each point of its orbit, moon 'falls' towards the
earth . So it must be attracted by the earth. 1.Wh at do you mean by free fall ?
Now when a body moves along a circular path,
When an object falls with a const ant
its velocity changes at every point, due to acceleration, under the influence of force of
chan ge in its direction i.e., a body moving in gravitation of the earth , object is said to have
circul ar path possesses acceleration. free fall.
The force that produces acceleration (called 2.Wh at is the acce lerati on of free fall ?
centripetal force) keep s the body moving along (Refer ques tion no 8 of exerc ise)
the circul ar path.
In the absence of centripetal force , the body 15.De fine acce lerati on due to gravi ty.
flies along a tangent. Newton reasoned that The acceleration produ ced in the motion of an
the centripetal force provided by the force of object falling unde r the force of gravity is called
attraction of the earth keeps the moon moving acceleration due to gravi ty. It is deno ted by g.
in its orbit by linking the fall of an apple to
16. Wha t is the value of 'g ' if an object is
circular motion of moon , Newton was led to the
proje cted vertic ally upwa rd and dropped
disco very of law of gravitation.
from top.
If an objec t is dropp ed down ward with an initial
2
NCER T BOOK QUES TION S PAGE: 102 veloc ity u=O,t hen a = g = 9.8 ms·
If an objec t is proje cted vertically upward with_
1. State the universal law of gravitation. an initial velocity u, then a = - g = - 9.8 ms··
Every object in the universe attracts every
Note :
other object with a force which is directly
proportional to the product of their masses and If the object will go to a maxim um height h
inversely proportiona l to the square of the where its final veloc ity beco mes zero ( v =O'
distan ce between their centers
•
Ill I '
IS . / · WI 1ere F = Cen tripe tal
r
For ce
v = Velocity of bod y
r = radius of circle.
m= mass
IX - ST D PHYSICS SSIGNMENT 7.What is Centripetal acc eler atio n?
When a bod y moves in a circular path then
9.GRAVITATION acceleration generated due to change in
its
velocity is kno wn as centripetal accelera
tion.
(Page - 01) The direction of centripetal acceleration
is
1.What is Gravity ? towards the centre of circle.
The force with which the earth pulls the
objects 8. What is the source of centripetal forc
towards it, is called the gravity or gravitatio e
nal that a plan et requires to revolve arou
force of eart h . nd the
Sun? On wha t factors doe s that force
depend?
2.Give few examples whe re gravitati
onal
force of the earth is responsible: Gravitational force is the sou rce of centripe
tal
I.Atmosphere above the earth. force required to revolve arou nd the sun
. This
II. Rain falling to the earth . force depends on the dist anc e between
the
Ill.Flow of wat er in rivers . planet and sun along with thei r masses.
If this
force becomes zero as a result of the abs
ence
3.What is Gra vita tion ? of centripetal force, the plan et would shif
t to
Gravitation is the forc e of attraction betw move tangentially outwards to the circ ular
een route
any two obje cts in the univ erse .
9.The earth is acted upon by gravitati
4.What is the main diff eren ce between on of
Sun , even though it doe s not fall into
gravitation and gravity ? the
Sun. Why?
Gravitation is the forc e of attraction betw Sur prov ides enough centripetal forc e to
een keep
any two obje cts in the univ erse . the earth in its orbit and the earth provides
centrifugal forc e due to its motion . The se
two
Gravity is the force of attraction between forces bala nce each other which prevents
any the
object and the earth. earth from falling into the sun .
5.What is Centripetal For ce? Write its 10.What is the weight of an object at the
centre of the earth of radius R?
expression.
Centripetal forc e is a forc e which causes At the centre of the earth acceleration due
to
acceleration of a body, mov ing in a circu gravity is zero . Since weight is the product
lar of
path and acti ng towards the centre of the mass and gravity. Weight of an object at
the
centre of the earth will be zero .
circular path .
6. Explain Cen trip etal forc e and write 11.What is Gravitational Constant? Wha
its t is
expression. its value?
i. Whe nev er a bod y mov es in a circular The gravitational constant G is numerica
lly
path , velocity and the direction equal to the force of grav itation which exis
ts
cha nge s at eve ry point. between two bod ies of unit masses kep t
at a
ii. The force that cau ses this unit dista nce from each other The value
of
acceleration and keeps the bod y universa l grav1tat1onal constant G 1s
mov ing along the ci rcular path acting G = 6 67 x 10 ·11 Nm 2 I Kg 2
tow ards the ce ntre .
J
, - -- -· --- -- -- - - ( ,'111 I Ill
(Pago - 02)
ti
12.W hy is Newt on 's law of gra vilali on co llod
the unive rsal law ?
G 1s constant of proportiona lity. It is called
Newton's law of gravit ation 1s called tile universal gravitation constant.
u111versal law because it is applicable to all
2. Write the formula to find the magnitude of
bodie s, wheth er the bodies are big or small, the gravitational force between the earth
wheth er they are celestial of terrestrial. and an object on the surface of the earth.
13. Suppose gravity of earth suddenly (i .M e X m ,,
beco mes zero, then in which direction will F gravitation = - - -2
r
the moon begin to move if no other celestial
body affects it? Where G is gravitational constant
If there is no gravitational pull from the earth,
Me = The mass of the earth
the moon starts to move in a straight line
tange nt to its circular path.
M0 = The mass of the object
r = the distance between the centre of
14.Ex plain briefly how Newton discovered
the Law of Gravitation . of the object and the centre of the earth .
Newt on observed while sitting under an apple
tree that an apple fell down. He asked himself ----------------------------- -·-- ---- ---- ---- -
that if the earth can attract an apple and can it NCER T BOOK QUES TIONS PAGE : 104
also attract the moon ? He then, argued that at
each point of its orbit, moon 'falls' towards the
earth . So it must be attracted by the earth. 1.Wh at do you mean by free fall ?
Now when a body moves along a circular path,
When an object falls with a const ant
its velocity changes at every point, due to acceleration, under the influence of force of
chan ge in its direction i.e., a body moving in gravitation of the earth , object is said to have
circul ar path possesses acceleration. free fall.
The force that produces acceleration (called 2.Wh at is the acce lerati on of free fall ?
centripetal force) keep s the body moving along (Refer ques tion no 8 of exerc ise)
the circul ar path.
In the absence of centripetal force , the body 15.De fine acce lerati on due to gravi ty.
flies along a tangent. Newton reasoned that The acceleration produ ced in the motion of an
the centripetal force provided by the force of object falling unde r the force of gravity is called
attraction of the earth keeps the moon moving acceleration due to gravi ty. It is deno ted by g.
in its orbit by linking the fall of an apple to
16. Wha t is the value of 'g ' if an object is
circular motion of moon , Newton was led to the
proje cted vertic ally upwa rd and dropped
disco very of law of gravitation.
from top.
If an objec t is dropp ed down ward with an initial
2
NCER T BOOK QUES TION S PAGE: 102 veloc ity u=O,t hen a = g = 9.8 ms·
If an objec t is proje cted vertically upward with_
1. State the universal law of gravitation. an initial velocity u, then a = - g = - 9.8 ms··
Every object in the universe attracts every
Note :
other object with a force which is directly
proportional to the product of their masses and If the object will go to a maxim um height h
inversely proportiona l to the square of the where its final veloc ity beco mes zero ( v =O'
distan ce between their centers
•
