Gravity, or gravitation, is a natural phenomenon by which all things with mass or energy—including planets, stars, galaxies, and even light—are brought toward one another. On Earth, gravity gives weight to physical objects, and the Moon's gravity causes the ocean tides.

1. GRAVITATION
Represented by- Radiate

2. INTRODUCTION
(Greek Civilization)
1. Socrates:
 He is Greek philosophers.
He is the first time started observing stars, suns and other
heavenly bodies.
2. Plato:
He was a student of Socrates and Plato also started
observing the same type of phenomena in the sky by
following the method or concept by the Socrates. ‘He followed
the path of Socrates’.
He was a great philosophers.

4. INTRODUCTION
3. Aristotle:
He was a student of Plato.
Alexander learnt from the Aristotle. He was a teacher of
Alexander.
He observed the sky, the motion if the sun, moon and
stars.
After the observation; He said that, The stars, moon, sun
and planets revolve around Earth.(without having
telescope)
This concept is named as Geocentric Model of Solar
System.
Till the time of Aristotle the planets also discovered. (4-5
planets observed)

5. INTRODUCTION
(Egyptian Civilization)
4. Ptolemy (King of Egypt):
He also supported Geocentric models.
He was the person who developed first geographical map.
He gave the concept that Earth is the sphere.
He worked on the concept of Birth of star.
These concept followed for long time.

6. Ptolemy

7. INTRODUCTION
5. Copernicus:
He was challenge the concept of given by Ptolemy.
He was challenges because, He was not able to understand
eclipse by Geocentric models.
He said that, if we have Geocentric model then eclipse
can never happen.
Since He was priest. He was not consider as philosophers.
After He died, his writing were made public, He declined
Geocentric model. But He never shows his concept to
anyone.
He suggested a new concept that Sun Centric Model,
because He was able to explain the concept of eclipse by
using this model.
He suggested circular orbits.

8. Copernicus

9. INTRODUCTION
[Denmark (Europe)]
6. Tycho Brahe (King of Denmark):
He was a person, who gave birth to the concept of
Astrology.
He said that planetary motion affect the human life.
He basically the two models of solar system.
He said that Sun revolve around the earth. Then He was
said that other planets revolve around the sun.
Moon revolve around the earth.
He also studied the high and low tides in the ocean.

10. Tycho Brahe

11. INTRODUCTION
(German)
7. Kepler (A German Mathematician):
He suggested the perfect model of Solar system by
Kepler law.
Three laws of Kepler;
a. First laws- Sun is centre and all planets revolve around the
sun in Elliptical orbit with sun at one of its Foci.

12. INTRODUCTION
b. Second law-
 Same area is swept is same time.
 then A1/t1 = A2/t2
 If t1 = t2
 then A1 = A2
c. Third law- T2∝ r3
Where, T= Time to complete one revolution
r= Average radius
If the average radius is increase the time period will
also increase.
The planets which has more distance from the sun will
have a bigger time period or will take more time to
complete one revolution.

13. Kepler

14. INTRODUCTION
(Italy)
8. Galileo:
He gave the concept of Displacement, Velocity,
Acceleration. He calculated the value of acceleration
due to gravity (g).
He challenge the concept that heavy body falls fast.
After demonstration, all bodies fall on earth with same
acceleration & at same time if they fall from same
height (climb in lining tower of pizza).
[Note- Air resistance do not play any role in gravitation]
He also developed pendulum clock. He also discovered
a telescope.
Galileo become blind during watching the sun on
telescope.

15. Galileo

16. INTRODUCTION
[(U.K.) LONDON]
9. Issac Newton:
 After Galileo, Newton followed and started the work from the
same point.
 He stated the work, where Galileo left them.
 He is the rebirth of Galileo.
 He discovered laws of motion.
 It was believed that these laws are applicable only to objects
present on earth.
 He said that, earth apply a force on every objects toward
itself.
 He apply this concept on moon’s motion.
 He then applied the same concept on other heavenly bodies.
 By using this concept, He successfully explained the motion of other
heavenly bodies. ‘Newton’s Law of Gravitation’ or ‘Universal
Law of Gravitation’.
 So Newton not able to give reason for existence of this law.

17. Issac Newton

18. Newton’s law of gravitation
This law states that, each and every body in the
universe which has some mass, attracts other
bodies towards itself. This is known as Universal
law of gravitation.
But the force applied by each body depends on its mass
and its distance from the other body.
Newton said two points-
1. Law of product of masses: F12
F ∝ m1m2 r
m1 F21 m2
2. Inverse square law:
F ∝ 1/r2 ; F ∝ m1m2/r2

19. Notes-
1. He said that, In the universe two bodies are attracting
each other towards themselves but the force of
attraction between them is directly proportional to
the product of their masses and it is inversely
proportional to square of distance between them. So it
simply means if distance become twice the force will
reduce by 4 times.
2. F ∝ m1m2 , It means consider this example of apple and
earth what will happen; the force between the earth and
apple it is directly proportional to mass of apple and
mass of earth. If the apple has more mass then force
would be more.
 F = G m1m2/r2 ; Universal equation of Gravitation

20. Free Fall
When you throw a ball upwards:-
The ball will reach some height.
After reaching some height the ball stop.
Then it will start falling on the ground.
While the falls on the ground, the force of Gravitation would be
applied.
Definitions- When an objects falls under the influence of
earth’s gravitational force only, then we call it as Free
Fall.
We have ignored the influence of air of any such particle.
In free fall the object will fall straight on the ground.
In free fall the earth will attracts object towards its centre.
F=ma; where, F= Force due to gravitation
a= Acceleration due to gravitation
In free fall the velocity of object will increase.