Maharashtra State Board: Class 10, 11
Definition: Gravitation
"Every particle of matter in the universe attracts every other particle with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them. The direction of the force is along the line joining the particles."
or
The force by which the Earth attracts objects towards its centre is called gravitational force.
Maharashtra State Board: Class 10, 11
Formula: Gravitation
Newton’s Universal Law of Gravitation:
F = \[G\frac{m_1m_2}{r^2}\]
where:
Maharashtra State Board: Class 11
Introduction
- Gravitation is the force of attraction that exists naturally between all material objects.
- Sir Isaac Newton discovered this force when he observed an apple falling vertically downward.
- He concluded that Earth attracts objects towards its center, causing them to fall vertically.
- This attraction applies not only to objects on Earth but also to celestial bodies like the Moon and planets.
- Gravitation is key to the Earth, Moon, and planets moving in their respective orbits.
Maharashtra State Board: Class 11
History/Origin
- Newton discovered the gravitational force after observing the falling apple.
- Indian astronomer Aryabhatta (476–550 A.D.) described Earth’s rotation and the orbits of the Moon and planets.
- Kepler formulated three laws describing planetary motion based on observations by Tycho Brahe.
- Newton explained these planetary motions using gravitation, providing the reason for the elliptical orbits of planets.
Maharashtra State Board: Class 11
Characteristics
- Gravitational force is always attractive.
- Has an infinite range.
- Acts along the line joining the centers of two masses.
- Does not depend on the medium between the objects.
- It is much weaker than other fundamental forces.
- Obeys Newton’s third law of motion (action = reaction).
- Causes celestial bodies to revolve in orbits due to centripetal force.
Maharashtra State Board: Class 11
Understanding Gravitation
- Newton proposed that the force causing an apple to fall acts on all objects, even at great distances like the Moon.
- This force keeps the Moon in orbit around Earth and planets around the Sun.
- The force magnitude decreases with the square of the distance, explaining why planets follow elliptical orbits.
- Kepler’s laws of planetary motion—laws of orbits, areas, and periods—describe these motions scientifically.
- Gravitation compels matter to coalesce, forming planets, stars, and other celestial bodies.
Maharashtra State Board: Class 11
Significance
- Explains why objects fall towards Earth.
- Responsible for the motion of planets, moons, and satellites.
- Enables the existence of stable orbits in the solar system.
- Explains phenomena like tides due to gravitational pull.
- Fundamental to understanding Earth’s gravity and weight.
Maharashtra State Board: Class 11
Real-Life Examples
- Apples falling from trees due to Earth’s gravitational pull.
- Motion of the Moon around Earth and satellites around planets.
- Planets revolving around the Sun in elliptical orbits.
- Water tides on Earth are influenced by the Moon’s gravity.
- Astronauts experience weightlessness in orbit because they are in free fall under gravity.
