Chapter 9: Gravitation
9.1 Understanding Gravitation
Gravitation is the force of attraction between any two objects in the universe. It is this force that keeps planets in orbit around the Sun and the Moon around the Earth.
9.2 Universal Law of Gravitation
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.
G (Constant) = 6.673 × 10⁻¹¹ N m²/kg²
9.3 Free Fall
Whenever objects fall towards the earth under gravity alone, they are in Free Fall. The acceleration due to gravity is denoted by g.
g = 9.8 m/s². It varies slightly from poles to equator due to the Earth's shape.
9.4 Mass vs Weight
Mass (m)
Measure of inertia. Remains constant everywhere in the universe. Scalar quantity.
Weight (W)
Force with which earth attracts an object (W = m × g). Varies with location. Vector quantity.
9.5 Pressure and Buoyancy
Thrust: Force acting perpendicular to a surface.
Pressure: Thrust per unit area (P = Thrust / Area).
When a body is immersed fully or partially in a fluid, it experiences an upward force (buoyancy) equal to the weight of the fluid displaced by it.
Key Examples
- Why a nail sinks but a ship floats.
- Lactometers used for milk purity.
- Hydrometers for liquid density.