Chapter: Gravitation - Class 9
Introduction
Gravitation is a natural phenomenon by which all things with mass or energy are brought
toward one another. It is the force that gives weight to physical objects and causes them to
fall towards the ground when dropped.
Key Concepts
1. Gravity: The force of attraction between two masses.
2. Universal Law of Gravitation: Every particle of matter in the universe attracts every
other particle with a force that is directly proportional to the product of their masses
and inversely proportional to the square of the distance between their centers.
3. Gravitational Constant (G): A proportionality constant used in the equation of the
law of gravitation.
4. Free Fall: The motion of a body where gravity is the only force acting upon it.
5. Acceleration due to Gravity (g): The acceleration of an object due to Earth's
gravity.
Universal Law of Gravitation
The universal law of gravitation states: F=Gm1m2r2F = G \frac{m_1 m_2}{r^2}F=Gr2m1m2
Where:
● FFF is the gravitational force between two masses.
● GGG is the gravitational constant (6.674×10−11 N m2 kg−26.674 \times 10^{-11} \,
\text{N} \, \text{m}^2 \, \text{kg}^{-2}6.674×10−11Nm2kg−2).
● m1m_1m1and m2m_2m2are the masses of the two objects.
● rrr is the distance between the centers of the two masses.
Importance of the Universal Law of Gravitation
1. Explains the motion of planets and satellites.
2. Describes the formation of tides.
3. Helps in understanding the orbits of celestial bodies.
4. Explains the structure and formation of galaxies.
Free Fall
When an object falls under the influence of gravity alone, it is said to be in free fall. In the
absence of air resistance, all objects fall at the same rate regardless of their mass.
Acceleration due to Gravity (g)
Introduction
Gravitation is a natural phenomenon by which all things with mass or energy are brought
toward one another. It is the force that gives weight to physical objects and causes them to
fall towards the ground when dropped.
Key Concepts
1. Gravity: The force of attraction between two masses.
2. Universal Law of Gravitation: Every particle of matter in the universe attracts every
other particle with a force that is directly proportional to the product of their masses
and inversely proportional to the square of the distance between their centers.
3. Gravitational Constant (G): A proportionality constant used in the equation of the
law of gravitation.
4. Free Fall: The motion of a body where gravity is the only force acting upon it.
5. Acceleration due to Gravity (g): The acceleration of an object due to Earth's
gravity.
Universal Law of Gravitation
The universal law of gravitation states: F=Gm1m2r2F = G \frac{m_1 m_2}{r^2}F=Gr2m1m2
Where:
● FFF is the gravitational force between two masses.
● GGG is the gravitational constant (6.674×10−11 N m2 kg−26.674 \times 10^{-11} \,
\text{N} \, \text{m}^2 \, \text{kg}^{-2}6.674×10−11Nm2kg−2).
● m1m_1m1and m2m_2m2are the masses of the two objects.
● rrr is the distance between the centers of the two masses.
Importance of the Universal Law of Gravitation
1. Explains the motion of planets and satellites.
2. Describes the formation of tides.
3. Helps in understanding the orbits of celestial bodies.
4. Explains the structure and formation of galaxies.
Free Fall
When an object falls under the influence of gravity alone, it is said to be in free fall. In the
absence of air resistance, all objects fall at the same rate regardless of their mass.
Acceleration due to Gravity (g)
