Skip to content
Know.itKnow.it
Create an animated lesson
On request

Read the answer free. Creating a lesson uses your daily or stored credits; review the language and settings before starting.

What is the universal law of gravitation?

Class 9 ScienceNCERT chapter: Gravitationइसे हिंदी में पढ़ें

Exam-ready answer

The universal law of gravitation states that every object in the universe attracts every other object with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. The force acts along the line joining their centres.

Explanation

Newton's universal law of gravitation says that any two objects attract each other. The force is proportional to the product of their masses: if either mass increases, the force increases. It is inversely proportional to the square of the distance between their centres: if distance doubles, the force becomes one-fourth.

Mathematically, F = G × (m1 × m2) / d^2, where G is the universal gravitational constant. Its value is 6.67 × 10^-11 N m^2 kg^-2. The force is always attractive and acts along the line joining the centres of the two objects.

For example, the gravitational force between the Sun and the Earth keeps the Earth in orbit. Similarly, the force between the Earth and an object on its surface gives the object its weight. This law applies to all objects, from tiny particles to planets.

Points to remember

  1. Every object attracts every other object with a gravitational force.
  2. Force is directly proportional to the product of masses: F ∝ m1 m2.
  3. Force is inversely proportional to the square of distance: F ∝ 1/d^2.
  4. Formula: F = G m1 m2 / d^2, where G = 6.67 × 10^-11 N m^2 kg^-2.
  5. The force is always attractive and acts along the line joining the centres.

Exam tip

Always write the formula F = G m1 m2 / d^2 with the correct SI unit of G. Mention that the force is attractive and acts along the line joining the centres to score full marks.

Questions students also ask

What is the value of G?
The universal gravitational constant G has a fixed value of 6.67 × 10^-11 N m^2 kg^-2. It is the same everywhere in the universe and does not depend on the masses or the distance between the objects.
Why is the gravitational force called universal?
It is called universal because it applies to all objects in the universe, whether they are small like a stone or large like a planet. The same law governs the motion of the Moon around the Earth and the falling of an apple.
How does distance affect gravitational force?
Gravitational force is inversely proportional to the square of the distance between the centres of two objects. If the distance is doubled, the force becomes one-fourth; if tripled, it becomes one-ninth.

Chapter labels help you find the topic in your textbook. Check your own edition: chapter names and order can change. These are Know.it explanations, not official NCERT solutions.