Notes on Gravitation Lecture

Introduction

• Movement disturbs the universe.
• Force in physics: push or pull.
• Everything in the universe interacts with gravitational force.

Basics of Gravitation

• Gravity: Invisible force pulling objects towards each other.
• Example: When a ball is dropped, it falls due to Earth's pull.
• All bodies with mass exert gravitational pull.

Gravitational Force Characteristics

1. Attractive Force: Gravitational force is always attractive.
   • Example: The Earth pulls the Moon; the Sun pulls the Earth.
2. Force at a Distance: No direct contact needed for gravitational pull.
   • Example: A ball dropped towards Earth.
3. Equal and Opposite Forces: Force exerted by two bodies is equal in magnitude but opposite in direction.
   • Example: Sun pulls Earth with a force of 1 billion Newton; Earth pulls Sun with the same force.
4. Independent of Medium: Gravitational force unaffected by intervening mediums (e.g., vacuum).
5. Independent of Other Bodies: The gravitational force between two masses is unaffected by the presence of other masses.
6. Acts along Line of Centers: The force acts along the line joining the center of masses of two bodies.
7. Long-range Force: The force decreases with distance according to the inverse square law but never reaches zero.
8. Weakest Force: Gravitational force is the weakest compared to other forces (electrostatic, magnetic, nuclear).

Gravitational Force Calculation

• Formula:
  F = G * (m1 * m2) / r²
  Where:
  • F = gravitational force
  • G = universal gravitational constant (6.67 x 10⁻¹¹ N m²/kg²)
  • m1, m2 = masses of the two bodies
  • r = distance between the centers of masses.

Example Calculation

• For two 1 kg books separated by 1 meter:
  F = 6.67 x 10⁻¹¹ N (very small force).

Conclusion

• Gravitational force is significant on a larger scale (e.g., between planets) but negligible at small distances due to other forces.
• Remember that everything in the universe attracts each other, highlighting the interconnectedness of all matter.

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