NEET Chapter-wise Notes: Gravitation

1. Introduction to Gravitation

Gravitation is the force of attraction between any two objects in the universe. It plays a crucial role in the motion of celestial bodies and the structure of the universe.

2. Newton's Universal Law of Gravitation

Newton proposed that every object in the universe attracts every other object with a force proportional to the product of their masses and inversely proportional to the square of the distance between them.

Formula:
F = G (m₁m₂) / r²

3. Kepler's Laws of Planetary Motion

Kepler formulated three important laws governing planetary motion:

• First Law (Law of Ellipses): Planets move in elliptical orbits with the Sun at one focus.
• Second Law (Law of Equal Areas): The line joining a planet to the Sun sweeps out equal areas in equal intervals of time.
• Third Law (Law of Harmonies): The square of the time period of a planet is proportional to the cube of the semi-major axis of its orbit.

4. Acceleration due to Gravity (g)

Acceleration experienced by a body due to Earth's gravitational force is called acceleration due to gravity (g).

Value: g ≈ 9.8 m/s²

5. Variation of g with Height and Depth

The value of g decreases as we move away from the Earth's surface and also decreases when we go deep inside the Earth.

6. Escape Velocity

Escape velocity is the minimum velocity required for an object to escape Earth's gravitational pull.

Formula:
v_e = √(2GM/R) ≈ 11.2 km/s for Earth

7. Orbital Velocity

Orbital velocity is the velocity required for an object to stay in orbit around a planet.

Formula:
v_o = √(GM/R)

8. Satellites and Geostationary Orbit

Satellites revolve around Earth in stable orbits. A geostationary satellite remains fixed relative to a point on Earth, making it useful for communication purposes.

9. Weightlessness in Space

In a freely falling system, the effective weight of a body becomes zero, leading to weightlessness experienced by astronauts in space.

10. Important Formulas in Gravitation

• F = G (m₁m₂) / r²
• g = GM / R²
• v_e = √(2GM/R)
• v_o = √(GM/R)
• T² ∝ r³ (Kepler's Third Law)

Conclusion

Gravitation is a fundamental force governing planetary motion, satellite dynamics, and space travel. Understanding these concepts is crucial for NEET aspirants.