This document discusses Newton's law of universal gravitation. It begins by stating the aims of understanding force of gravitation and deriving the mathematical law. It then defines gravity as a force that causes every object in the universe to attract each other. The key points are that Newton's law states that the gravitational force between two objects is directly proportional to their masses and inversely proportional to the square of the distance between them. The document derives the gravitational formula and notes that gravitational force is very small between everyday objects, which is why we do not notice it.

1. GRAVITATION

2. Aims
By the end of this unit we will come to:
• Know about Force of Gravitation.
• Understand and derive the mathematical Law of Gravitation.

3. Force of Gravitation
• There exists a force due to which everybody of the universe attracts
every other body.
• This force is called force of gravitation.

4. Self-Assessment Questions
1.Force with which everybody attracts every other body is called:
(a) force of friction (b) retarding force
(c) force of gravitation (d) none of them
Answer:
(c)
force
of
gravitation

5. LAW OF GRAVITATION
• According to Newton's Law of Universal Gravitation:
“Everybody in the universe attracts every other body with a force
which is directly proportional to the product of their masses and
inversely proportional to the square of the distance between their
centres.”
Two Points
1. A force which is directly proportional to the product of their masses
2. Inversely proportional to the square of the distance between their
centres.

6. Derivation of Formula
In SI units its value is 6.673  10-11 Nm2 kg-2.
Note: Due to small value of G, the gravitational force of attraction between
objects around us is very small and we do not feel it.
1 2
2
1 2
2
1 2
2
1
F m m
F
d
Oncombining abovetwoequations
m m
F
d
m m
F G
d





7. Self-Assessment Questions.
1. The Universal law of gravitation must apply to?
(a) The earth and the apple (b) Any pair of bodies
(c) The earth and the moon (d) The planets around the Sun
Answer:
Any
pair
of
bodies

8. Assignment
1. State Newton's law of gravitation.
2. Write Mathematics form Newton's law of gravitation
3. Explain the law of gravitation.
4. Why do we do not feel gravitational force of attraction between
objects around us