What is Newton's law of gravitation Class 9?

Sir Isaac Newton’s Universal Law of Gravitation explains how every object in the universe attracts every other object. It connects daily phenomena like falling bodies and tides with celestial motion such as planets and satellites.

Statement of the Law

Every object attracts every other object with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres. The force acts along the line joining the centres.

Mathematical Form

F = G · (m₁ m₂) / r²

F: gravitational force

m₁, m₂: masses |

r: distance between centres |

G: universal constant = 6.67 × 10⁻¹¹ N m² kg⁻²

Key Features

• Universal: applies to stars, planets, and everyday objects.
• Attractive: gravity always pulls, never pushes.
• Mutual: forces are equal and opposite on the two bodies.
• Depends on mass and distance: more mass → stronger pull; more distance → weaker pull.

Everyday Examples

• Falling objects: a ball drops due to Earth’s gravity.
• Planetary orbits: Earth revolves around the Sun.
• Tides: Moon’s and Sun’s gravity raise ocean tides.
• Satellites: remain in orbit by gravity–motion balance.

Why It Matters in Class 9

• Builds foundation for topics like weight, escape velocity, and satellites.
• Explains that weight = m g is Earth’s gravitational pull on a body.
• Links real applications: rockets, tides, and apparent weightlessness.

Scientific Significance

Kepler described planetary motion; Newton explained why it occurs. His law unified terrestrial and celestial mechanics under one principle—one of science’s greatest achievements.

Limitations

• Assumes action at a distance (no propagation time).
• Less accurate in extremely strong fields or at relativistic scales.
• Einstein’s General Relativity refines gravity in such regimes.