Gravity is a natural force of attraction between any two masses. It pulls objects toward each other and is responsible for keeping us grounded on Earth and for the motion of celestial bodies.
Key Concepts
Gravitational Force (F): The force between two masses.
Acceleration due to gravity (g): On Earth, g = 9.8 m/s²
Weight (W): Force of gravity acting on an object → W = m × g
Universal Law of Gravitation: F = G × (m₁ × m₂) / r²
Where G = 6.674 × 10⁻¹¹ Nm²/kg²
Solved Examples
Example 1:
What is the weight of a 10 kg object on Earth? Solution: W = m × g = 10 × 9.8 = 98 N
Example 2:
Find the gravitational force between two 5 kg masses 2 m apart. Solution:
F = G × (5 × 5) / 2² = 6.674 × 10⁻¹¹ × 25 / 4 = 4.17 × 10⁻¹⁰ N
Example 3:
How fast does a 2 kg object accelerate when dropped? Solution: a = g = 9.8 m/s²
Example 4:
How long does it take an object to fall 19.6 m? Solution:
s = ½gt² → 19.6 = ½ × 9.8 × t² → t²