For educational Purpose

2. • Definition for Gravitation
• Acceleration Due to Gravity
• Variation Of “G” With Respect to Height And Depth
• Escape Velocity
• Orbital Velocity
• Gravitational Potential
• Time period of a Satellite
• Height of Satellite
• Binding Energy
• Various Types of Satellite
• Kepler’s Law of Planetary motion

5. • The rotation of the earth around the sun or that of the moon
around earth is explained on the basis of this law.
• The tide are formed in ocean due to the gravitational
force of attraction between earth and the moon.
• The value of g can be used to predict the orbits and time
period of an satellite.
Attraction Force between two bodies

6. • The Gravitation force between two masses is independent
of the intervening medium.
• The mutual gravitational forces between two bodies are
equal and opposite i.e. Gravitational Forces obey Newton’s
third law of motion.
• The gravitational force is an conservative force.
• The law of gravitation holds only for point masses.
• The gravitational force between two point masses is a
central force. Its magnitude depends only on r and has no
angular dependence .
• The Gravitational force between two bodies is independent
of the presence of other bodies.

7. • Consider an Elevator freely falling from North pole to
South pole through the center of earth. Describe its
motion??
• For answer Press Enter ..

13.  The Variation of g with respect to Depth and Height
(graph).
 The Variation of g with respect to height will never be
zero. It will increase after certain height.
 The Variation of g with respect to depth will be zero
when the body is placed at the center of earth.

15. Gravitational field
• Gravitational field . Two bodies attract each other by the
gravitational force even if they are not in direct contact. This
interaction is called action at a distance. It can best
explained in terms of concept of field. According to the field
concept.
– Every mass modifies the space around it . This modified space is called
gravitational field
– When any other mass is placed in this field , it feels a gravitational force of
attraction due to its interaction with the gravitational field
• The space surrounding a material body within which its
gravitational force of attraction can be experiences a force of
attraction towards the centre of earth

16. Gravitational Potential Energy
A
dx
B
P
x
r
R
O

18. • If we throw a ball into air , it rises to a certain height and falls
back. If we throw it with a greater velocity , it will rise higher
before falling down. If we throw with sufficient velocity , it will
never come back . i.e. It will escape from the gravitational pul
of the earth.
• The minimum velocity required to do so is called escape
velocity.
• Consider the earth to be a sphere of mass M and radius R
with centre O.

21. • Can you tell why moon has no atmosphere ??
• For answer press enter
• Due to the small value of g. The escape velocity in the
moon is 2.38 km/s . The air molecules have thermal velocity
is greater than the escape velocity and therefore air
molecules escape.

22. Satellite
Artificial Natural
Geostationary Polar

23. • Satellite is an body which continuously revolves on it own
around and a much larger body in a stable orbit.
• Natural satellites : A satellite created by nature is called
natural satellite . example : moon.
• Artificial satellite : A man made satellite is called an artificial
satellite. Example Chandrayaan .
• World’s Frist satellite was SPUTNIK-1.

24. • Principle for launching a satellite : Consider a high tower
with its top projecting outside the earth’s atmosphere.
• Lets throw a body horizontally from the top of the tower with
different velocities.
• As we increase the velocity of horizontal projection , the
body will hit the ground at point farther and farther from the
foot of the tower.
• At certain velocity the body will not hit the ground , but
always be in a state of free fall under the influence of the
gravity.
• Then the body will follow a stable circular orbit . And that
body is called satellite.

25. Click on the video

26. • Orbital velocity is the velocity required to put
the satellite into its orbit around earth

27. Vo
R R+h
h

30. • A satellite which revolves around the earth in tis equatorial
plane with the same angular speed and in the same
direction as the earth rotates about its own axis is called a
geostationary or synchronous satellite.

31. • It should revolve in an orbit concentric and coplanar with
the equatorial plane of the earth.
• Its sense of rotation should be same as that of the earth ,
i.e From west to east.
• Its period of revolution around the earth should be exactly
same as that of the earth about its own axis , i.e 24 hours
• It should revolve at a height of exactly 35930 km.

32. • In communicating radio,T.V and telephone signals across
the world.
• In studying the upper regions of the atmosphere.
• In Forecasting weather.
• In studying meteorites.
• In studying solar radiation and cosmic rays.
• And used in GPS (Global positioning System).

33. • A satellite that revolves in a planar orbit is called a polar
satellite. Eg IERS (Indian earth resources satellites)
• Uses of Polar satellite
– Polar satellites are used in weather and environment monitoring.
– Spying
– Study topography of other celestial
bodies

36. • Law of orbits (first law) : Each planet revolves around the
sun in an elliptical orbit with the sun situated at the one of
the two foci.

37. • Law of areas (second law) : The radius vector drawn from
the sun to a planet sweeps out equal areas in equal
intervals of time i.e the areal velocity ( area covered per
unit time) of a planet around the sun is constant.

38. P’
planet
sun