Topic 7: One-Page Revision Sheet

Chapter 5: Laws of Gravitation – One Page Revision

1. Gravitation

Gravitation is the force of attraction between any two bodies having mass. It is a universal and always attractive force.

2. Newton’s Law of Gravitation

Every particle 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.

Formula:
F = G (m₁ m₂) / r²

Gravitational Constant:
G = 6.67 × 10⁻¹¹ N m² kg⁻²

3. Acceleration Due to Gravity (g)

Acceleration produced in a body due to Earth's gravitational pull.

Value:
g = 9.8 m s⁻² (≈ 10 m s⁻² for numericals)

Relation with G:
g = G M / R²

4. Mass and Weight

Mass

• Quantity of matter
• Scalar quantity
• Constant everywhere
• SI unit: kg

Weight

• Gravitational force acting on a body
• Vector quantity
• Varies from place to place
• SI unit: newton (N)

Relation: W = m g

On Moon:
Weight on Moon = (1/6) × Weight on Earth
Mass remains same.

5. Variation of Acceleration Due to Gravity

With Height

As height increases, g decreases.

With Depth

As depth increases, g decreases.
At centre of Earth, g = 0.

With Latitude

• g is maximum at poles
• g is minimum at equator

6. Gravitational Potential Energy

Energy possessed by a body due to its position in Earth's gravitational field.

Formula:
PE = m g h

SI unit: Joule (J)

During free fall, gravitational potential energy converts into kinetic energy.

7. Important CET Points

• Numericals from F = G m₁ m₂ / r²
• Difference between mass and weight
• Moon-related weight questions
• Conceptual MCQs on variation of g
• Use g = 10 m s⁻² unless stated otherwise