Gravitation

CLASS 9 PHYSICS

1. GRAVITATION
PHYSICS

2. CENTRIPETAL FORCE
★IN CIRCULAR MOTION , THE DIRECTION KEEPS CHANGING.
★BECAUSE OF THE CONTINUOUS CHANGE IN DIRECTION , THE VELOCITY ALSO KEEPS ON
CHANGING.
★A FORCE CALLED CENTRIPETAL FORCE ACTS UPON THE OBJECT WHICH IS IN CIRCULAR
MOTION .
★THE FORCE IS GENERATED FROM THE CENTRE OF THE CIRCULAR PATH.
★WITHOUT CENTRIPETAL FORCE,AN OBJECT CANNOT MOVE IN CIRCULAR MOTION.
★FOR EG: MOTION OF MOON AROUND THE EARTH.

3. NEWTON’S UNIVERSAL LAW OF GRAVITATION
★ACCORDING TO NEWTON’S UNIVERSAL LAW OF GRAVITATION ,THERE IS A FORCE OF
ATTRACTION BETWEEN EVERY TWO OBJECTS IN THE UNIVERSE.
★THE FORCE OF ATTRACTION BETWEEN ANY TWO OBJECTS IN THE UNIVERSE IS DIRECTLY
PROPORTIONAL TO THE PRODUCT OF THEIR MASSES. F∝ m1m2
★THE FORCE OF ATTRACTION BETWEEN TWO BODIES IS INVERSELY PROPORTIONAL TO THE
SQUARE OF THE DISTANCE BETWEEN THEM. F∝1/R^2 .

4. DERIVATION OF THE EQUATION [ F= G * m1m2 /R^2 ]
F ∝ m1m2……...1
F ∝ 1/ R^2……….2
BY EQUATION 1 AND 2
F ∝ m1m2 / R^2

F = G * m1m2 / R^2

5. UNIVERSAL GRAVITATIONAL CONSTANT
‘ G ‘ IS CALLED THE UNIVERSAL GRAVITATIONAL CONSTANT.
THIS VALUE WAS FIRST GIVEN BY HENRY CAVENDISH


6.67* 10 ^-11= G
G= F * R^2 / m1m2
[ G = Nm2 / kg^2 ]
[ G = Nm^2 * kg^2 ]
G

6. APPLICATIONS OF UNIVERSAL LAW OF GRAVITATION
IT EXPLAINS :
➢EARTH’S GRAVITATIONAL FORCE [ g ]
➢MOVEMENT OF MOON AROUND EARTH
➢REVOLUTION OF ALL PLANETS AROUND THE SUN .
➢THE REASON OF TIDES AND WAVES BECAUSE OF THE SUN AND MOON .

7. EQUATIONS OF MOTION UNDER THE EFFECT OF GRAVITY
1.V = U + AT V = U + GT
2.S = U T+ ½ AT^2 S = UT + ½ GT^2
3.V^2 = U^2 + 2AS V^2 = U^2 + 2GS
EQUATIONS OF MOTION UNDER SPECIAL CONDITIONS
1.INITIAL VELOCITY IS ZERO 2. WHEN THE OBJECT MOVES UPWARD
➔V = GT #V = U - GT
➔S = ½ GT^2 #S = UT - ½ GT^2
➔V^2 = 2GS #V^2 = U^2 - 2GS

8. FREEFALL
WHEN AN OBJECT IS DROPPED DIRECTLY FROM A CERTAIN HEIGHT ,IT GETS
ATTRACTED TOWARDS THE SURFACE OF THE EARTH BECAUSE OF EARTH’S GRAVITY .
THIS FALLING OF AN OBJECT TOWARDS THE EARTH’S SURFACE UNDER THE EFFECT OF
EARTH’S GRAVITATIONAL FORCE IS CALLED AS FREEFALL.

9. ACCELERATION DUE TO GRAVITY [ g ]
WHEN A BODY GOES UNDER FREEFALL , AN ACCELERATION IS PRODUCED IN IT BECAUSE OF
THE GRAVITATIONAL FORCE OF ATTRACTION OF EARTH . THIS ACCELERATION IS CALLED AS
ACCELERATION DUE TO GRAVITY. IT IS DENOTED BY ‘ g ‘ .

MASS
VELOCITY
ACCELERATION
MASS
VELOCITY
ACCELERATION DUE TO GRAVITY
HORIZONTAL
VERTICAL

10. ACCELERATION DUE TO GRAVITY [ g ]
1.ITS SI UNIT IS M/S^2.
2.ITS VALUE IS 9.8 M/S^2.
3.ITS VALUE IS NOT CONSTANT I.E. ITS VALUE CHANGES FROM PLACE TO PLACE.
4.THIS VALUE IS INDEPENDENT OF THE MASS OF THE FALLING OBJECT.
5.THIS VALUE IS MAXIMUM AT THE POLES AND MINIMUM AT THE EQUATOR.
6.THE VALUE OF g IS ZERO AT THE CENTRE OF THE EARTH.

11. VERTICAL MOVEMENT OF AN OBJECT AND THE RESULTANT
FORCE


F = M * A

F = M * G
F = M * A

F = M * -G

12. MASS VS. WEIGHT


1.IT IS THE MEASURE OF THE AMOUNT OF 1. THE FORCE ACTING ON A BODY DUE TO
MATTER IN A BODY. ACCELERATION DUE TO GRAVITY.
2.MASS IS DENOTED BY “M”.
3.THE SI UNIT IS KG [ KILOGRAM ].
4.IT DOES NOT CHANGE UNDER GRAVITY.
5.IT IS A SCALAR QUANTITY.
6.MASS CAN NEVER BE ZERO.




2. WEIGHT IS DENOTED BY “W”.
3. THE SI UNIT IS N [ NEWTON ].
4. IT CHANGES UNDER THE EFFECT OF
GRAVITY.
5. IT IS A VECTOR QUANTITY.
6. WEIGHT CAN BE ZERO.

13. RELATIONSHIP BETWEEN “ G “ AND “ g “.


F = G* Mm / r^2
m * a = G* Mm / r^2
∴ g = G * Mass of EARTH / Radius of EARTH^2

14. GRAVITY VS. GRAVITATION








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15. “ g “ VS. “ G “









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16. GRAVITY OF MOON [ GRAVITATIONAL FORCE OF MOON ]


g-e =GRAVITY OF EARTH
g-m =GRAVITY OF MOON
g-m≈g-e/6

> WEIGHT DEPENDS UPON GRAVITY.SO,
Wm ≈ We/6

17. MORE ON EARTH


MASS OF EARTH = 6 * 10^24 Kg
RADIUS OF EARTH = 6 * 10^6 Km

18. KEPLER’S THREE LAWS OF MOTION